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icefall/egs/librispeech/ASR/zipformer/zipformer.py
Erwan Zerhouni 807816fec0
Fix chunk issue for sherpa (#1316)
2023-10-18 16:07:10 +08:00

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#!/usr/bin/env python3
# Copyright 2022-2023 Xiaomi Corp. (authors: Daniel Povey,
# Zengwei Yao)
#
# See ../../../../LICENSE for clarification regarding multiple authors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import copy
import logging
import math
import random
import warnings
from typing import List, Optional, Tuple, Union
import torch
from encoder_interface import EncoderInterface
from scaling import (
Identity, # more friendly to backward hooks than nn.Identity(), for diagnostic reasons.
)
from scaling import (
ScaledLinear, # not as in other dirs.. just scales down initial parameter values.
)
from scaling import (
ActivationDropoutAndLinear,
Balancer,
BiasNorm,
ChunkCausalDepthwiseConv1d,
Dropout2,
FloatLike,
ScheduledFloat,
Whiten,
convert_num_channels,
limit_param_value,
penalize_abs_values_gt,
softmax,
)
from torch import Tensor, nn
class Zipformer2(EncoderInterface):
"""
Args:
Note: all "int or Tuple[int]" arguments below will be treated as lists of the same length
as downsampling_factor if they are single ints or one-element tuples. The length of
downsampling_factor defines the number of stacks.
output_downsampling_factor (int): how much to downsample at the output. Note:
we also downsample by a factor of 2 in the Conv2dSubsampling encoder.
You should probably leave this at 2.
downsampling_factor (Tuple[int]): downsampling factor for each encoder stack.
Note: this is in addition to the downsampling factor of 2 that is applied in
the frontend (self.encoder_embed).
encoder_dim (Tuple[int]): embedding dimension of each of the encoder stacks, one per
encoder stack.
num_encoder_layers (int or Tuple[int])): number of encoder layers for each stack
encoder_unmasked_dim (int or Tuple[int]): unmasked dimension in each of
the encoder stacks for purposes of per-frame dropout (recommend 256 for
now).
query_head_dim (int or Tuple[int]): dimension of query and key per attention
head: per stack, if a tuple..
pos_head_dim (int or Tuple[int]): dimension of positional-encoding projection per
attention head
value_head_dim (int or Tuple[int]): dimension of value in each attention head
num_heads: (int or Tuple[int]): number of heads in the self-attention mechanism.
Must be at least 4.
feedforward_dim (int or Tuple[int]): hidden dimension in feedforward modules
cnn_module_kernel (int or Tuple[int])): Kernel size of convolution module
pos_dim (int): the dimension of each positional-encoding vector prior to projection,
e.g. 128.
dropout (float): dropout rate
warmup_batches (float): number of batches to warm up over; this controls
dropout of encoder layers.
causal (bool): if True, support chunkwise causal convolution. This should
not hurt WER as no modeling power is lost, but the convolution modules will be
slightly slower and use more memory. Enables use of the chunk_size and
left_context_chunks options in forward(), which simulates streaming
decoding.
chunk_size: (list of int): only set this to other than [-1] if causal;
the chunk size will be randomly chosen from this list. -1 means no chunking.
left_context_frames: (list of int): determines the number of left-
context chunks for causal training; will be rounded to a number of
chunks. Must not be less than cnn_module_kernel (after factoring in
rounding and downsampling); an error will be thrown if this is violated.
"""
def __init__(
self,
output_downsampling_factor: int = 2,
downsampling_factor: Tuple[int] = (2, 4),
encoder_dim: Union[int, Tuple[int]] = 384,
num_encoder_layers: Union[int, Tuple[int]] = 4,
encoder_unmasked_dim: Union[int, Tuple[int]] = 256,
query_head_dim: Union[int, Tuple[int]] = 24,
pos_head_dim: Union[int, Tuple[int]] = 4,
value_head_dim: Union[int, Tuple[int]] = 12,
num_heads: Union[int, Tuple[int]] = 8,
feedforward_dim: Union[int, Tuple[int]] = 1536,
cnn_module_kernel: Union[int, Tuple[int]] = 31,
pos_dim: int = 192,
dropout: FloatLike = None, # see code below for default
warmup_batches: float = 4000.0,
causal: bool = False,
chunk_size: Tuple[int] = [-1],
left_context_frames: Tuple[int] = [-1],
) -> None:
super(Zipformer2, self).__init__()
if dropout is None:
dropout = ScheduledFloat((0.0, 0.3), (20000.0, 0.1))
def _to_tuple(x):
"""Converts a single int or a 1-tuple of an int to a tuple with the same length
as downsampling_factor"""
if isinstance(x, int):
x = (x,)
if len(x) == 1:
x = x * len(downsampling_factor)
else:
assert len(x) == len(downsampling_factor) and isinstance(x[0], int)
return x
self.output_downsampling_factor = output_downsampling_factor # int
self.downsampling_factor = downsampling_factor # tuple
self.encoder_dim = encoder_dim = _to_tuple(encoder_dim) # tuple
self.encoder_unmasked_dim = encoder_unmasked_dim = _to_tuple(
encoder_unmasked_dim
) # tuple
num_encoder_layers = _to_tuple(num_encoder_layers)
self.num_encoder_layers = num_encoder_layers
self.query_head_dim = query_head_dim = _to_tuple(query_head_dim)
self.value_head_dim = value_head_dim = _to_tuple(value_head_dim)
pos_head_dim = _to_tuple(pos_head_dim)
self.num_heads = num_heads = _to_tuple(num_heads)
feedforward_dim = _to_tuple(feedforward_dim)
self.cnn_module_kernel = cnn_module_kernel = _to_tuple(cnn_module_kernel)
self.causal = causal
self.chunk_size = chunk_size
self.left_context_frames = left_context_frames
for u, d in zip(encoder_unmasked_dim, encoder_dim):
assert u <= d
# each one will be Zipformer2Encoder or DownsampledZipformer2Encoder
encoders = []
num_encoders = len(downsampling_factor)
for i in range(num_encoders):
encoder_layer = Zipformer2EncoderLayer(
embed_dim=encoder_dim[i],
pos_dim=pos_dim,
num_heads=num_heads[i],
query_head_dim=query_head_dim[i],
pos_head_dim=pos_head_dim[i],
value_head_dim=value_head_dim[i],
feedforward_dim=feedforward_dim[i],
dropout=dropout,
cnn_module_kernel=cnn_module_kernel[i],
causal=causal,
)
# For the segment of the warmup period, we let the Conv2dSubsampling
# layer learn something. Then we start to warm up the other encoders.
encoder = Zipformer2Encoder(
encoder_layer,
num_encoder_layers[i],
pos_dim=pos_dim,
dropout=dropout,
warmup_begin=warmup_batches * (i + 1) / (num_encoders + 1),
warmup_end=warmup_batches * (i + 2) / (num_encoders + 1),
final_layerdrop_rate=0.035 * (downsampling_factor[i] ** 0.5),
)
if downsampling_factor[i] != 1:
encoder = DownsampledZipformer2Encoder(
encoder,
dim=encoder_dim[i],
downsample=downsampling_factor[i],
dropout=dropout,
)
encoders.append(encoder)
self.encoders = nn.ModuleList(encoders)
self.downsample_output = SimpleDownsample(
max(encoder_dim), downsample=output_downsampling_factor, dropout=dropout
)
def get_feature_masks(self, x: Tensor) -> Union[List[float], List[Tensor]]:
"""
In eval mode, returns [1.0] * num_encoders; in training mode, returns a number of
randomized feature masks, one per encoder.
On e.g. 15% of frames, these masks will zero out all enocder dims larger than
some supplied number, e.g. >256, so in effect on those frames we are using
a smaller encoer dim.
We generate the random masks at this level because we want the 2 masks to 'agree'
all the way up the encoder stack. This will mean that the 1st mask will have
mask values repeated self.zipformer_subsampling_factor times.
Args:
x: the embeddings (needed for the shape and dtype and device), of shape
(1, batch_size, encoder_dims0)
"""
num_encoders = len(self.encoder_dim)
if not self.training:
return [1.0] * num_encoders
(num_frames0, batch_size, _encoder_dims0) = x.shape
assert self.encoder_dim[0] == _encoder_dims0, (
self.encoder_dim[0],
_encoder_dims0,
)
feature_mask_dropout_prob = 0.125
# mask1 shape: (1, batch_size, 1)
mask1 = (
torch.rand(1, batch_size, 1, device=x.device) > feature_mask_dropout_prob
).to(x.dtype)
# mask2 has additional sequences masked, about twice the number.
mask2 = torch.logical_and(
mask1,
(
torch.rand(1, batch_size, 1, device=x.device)
> feature_mask_dropout_prob
).to(x.dtype),
)
# dim: (1, batch_size, 2)
mask = torch.cat((mask1, mask2), dim=-1)
feature_masks = []
for i in range(num_encoders):
channels = self.encoder_dim[i]
feature_mask = torch.ones(
1, batch_size, channels, dtype=x.dtype, device=x.device
)
u1 = self.encoder_unmasked_dim[i]
u2 = u1 + (channels - u1) // 2
feature_mask[:, :, u1:u2] *= mask[..., 0:1]
feature_mask[:, :, u2:] *= mask[..., 1:2]
feature_masks.append(feature_mask)
return feature_masks
def get_chunk_info(self) -> Tuple[int, int]:
"""
Returns chunk_size and left_context_chunks.
"""
if not self.causal:
return -1, -1
if torch.jit.is_scripting() or torch.jit.is_tracing():
assert len(self.chunk_size) == 1, self.chunk_size
chunk_size = self.chunk_size[0]
else:
chunk_size = random.choice(self.chunk_size)
if chunk_size == -1:
left_context_chunks = -1
else:
if torch.jit.is_scripting() or torch.jit.is_tracing():
assert len(self.left_context_frames) == 1, self.left_context_frames
left_context_frames = self.left_context_frames[0]
else:
left_context_frames = random.choice(self.left_context_frames)
# Note: in Python, -1 // n == -1 for n > 0
left_context_chunks = left_context_frames // chunk_size
if left_context_chunks == 0:
left_context_chunks = 1
return chunk_size, left_context_chunks
def forward(
self,
x: Tensor,
x_lens: Tensor,
src_key_padding_mask: Optional[Tensor] = None,
) -> Tuple[Tensor, Tensor]:
"""
Args:
x:
The input tensor. Its shape is (seq_len, batch_size, feature_dim).
x_lens:
A tensor of shape (batch_size,) containing the number of frames in
`x` before padding.
src_key_padding_mask:
The mask for padding, of shape (batch_size, seq_len); True means
masked position. May be None.
Returns:
Return a tuple containing 2 tensors:
- embeddings: its shape is (output_seq_len, batch_size, max(encoder_dim))
- lengths, a tensor of shape (batch_size,) containing the number
of frames in `embeddings` before padding.
"""
outputs = []
if torch.jit.is_scripting() or torch.jit.is_tracing():
feature_masks = [1.0] * len(self.encoder_dim)
else:
feature_masks = self.get_feature_masks(x)
chunk_size, left_context_chunks = self.get_chunk_info()
if torch.jit.is_scripting() or torch.jit.is_tracing():
# Not support exporting a model for simulating streaming decoding
attn_mask = None
else:
attn_mask = self._get_attn_mask(x, chunk_size, left_context_chunks)
for i, module in enumerate(self.encoders):
ds = self.downsampling_factor[i]
x = convert_num_channels(x, self.encoder_dim[i])
x = module(
x,
chunk_size=chunk_size,
feature_mask=feature_masks[i],
src_key_padding_mask=(
None
if src_key_padding_mask is None
else src_key_padding_mask[..., ::ds]
),
attn_mask=attn_mask,
)
outputs.append(x)
# if the last output has the largest dimension, x will be unchanged,
# it will be the same as outputs[-1]. Otherwise it will be concatenated
# from different pieces of 'outputs', taking each dimension from the
# most recent output that has it present.
x = self._get_full_dim_output(outputs)
x = self.downsample_output(x)
# class Downsample has this rounding behavior..
assert self.output_downsampling_factor == 2, self.output_downsampling_factor
if torch.jit.is_scripting() or torch.jit.is_tracing():
lengths = (x_lens + 1) // 2
else:
with warnings.catch_warnings():
warnings.simplefilter("ignore")
lengths = (x_lens + 1) // 2
return x, lengths
def _get_attn_mask(
self, x: Tensor, chunk_size: int, left_context_chunks: int
) -> Optional[Tensor]:
"""
Return None if chunk_size == -1, else return attention mask of shape
(seq_len, seq_len), interpreted as (tgt_seq_len, src_seq_len). True
means a masked position.
Args:
x: embeddings after self.encoder_embed(), of shape (seq_len, batch_size, embed_dim).
chunk_size: chunk size, must divide
"""
if chunk_size <= 0:
return None
assert all(chunk_size % d == 0 for d in self.downsampling_factor)
if left_context_chunks >= 0:
num_encoders = len(self.encoder_dim)
assert all(
chunk_size * left_context_chunks
>= (self.cnn_module_kernel[i] // 2) * self.downsampling_factor[i]
for i in range(num_encoders)
)
else:
left_context_chunks = 1000000
seq_len = x.shape[0]
# t is frame index, shape (seq_len,)
t = torch.arange(seq_len, dtype=torch.int32, device=x.device)
# c is chunk index for each frame, shape (seq_len,)
if torch.jit.is_scripting() or torch.jit.is_tracing():
c = t // chunk_size
else:
with warnings.catch_warnings():
warnings.simplefilter("ignore")
c = t // chunk_size
src_c = c
tgt_c = c.unsqueeze(-1)
attn_mask = torch.logical_or(src_c > tgt_c, src_c < tgt_c - left_context_chunks)
if __name__ == "__main__":
logging.info(f"attn_mask = {attn_mask}")
return attn_mask
def _get_full_dim_output(self, outputs: List[Tensor]):
num_encoders = len(self.encoder_dim)
assert len(outputs) == num_encoders
output_dim = max(self.encoder_dim)
output_pieces = [outputs[-1]]
cur_dim = self.encoder_dim[-1]
for i in range(num_encoders - 2, -1, -1):
d = self.encoder_dim[i]
if d > cur_dim:
this_output = outputs[i]
output_pieces.append(this_output[..., cur_dim:d])
cur_dim = d
assert cur_dim == output_dim
return torch.cat(output_pieces, dim=-1)
def streaming_forward(
self,
x: Tensor,
x_lens: Tensor,
states: List[Tensor],
src_key_padding_mask: Tensor,
) -> Tuple[Tensor, Tensor, List[Tensor]]:
"""
Args:
x:
The input tensor. Its shape is (seq_len, batch_size, feature_dim).
x_lens:
A tensor of shape (batch_size,) containing the number of frames in
`x` before padding.
states: list of cached tensors of all encoder layers. For layer-i,
states[i*6:(i+1)*6] is (cached_key, cached_nonlin_attn, cached_val1, cached_val2,
cached_conv1, cached_conv2).
src_key_padding_mask:
The mask for padding, of shape (batch_size, seq_len); True means
masked position. May be None.
Returns:
Return a tuple containing 2 tensors:
- embeddings: its shape is (output_seq_len, batch_size, max(encoder_dim))
- lengths, a tensor of shape (batch_size,) containing the number
of frames in `embeddings` before padding.
- updated states
"""
outputs = []
new_states = []
layer_offset = 0
for i, module in enumerate(self.encoders):
num_layers = module.num_layers
ds = self.downsampling_factor[i]
x = convert_num_channels(x, self.encoder_dim[i])
x, new_layer_states = module.streaming_forward(
x,
states=states[layer_offset * 6 : (layer_offset + num_layers) * 6],
left_context_len=self.left_context_frames[0] // ds,
src_key_padding_mask=src_key_padding_mask[..., ::ds],
)
layer_offset += num_layers
outputs.append(x)
new_states += new_layer_states
# if the last output has the largest dimension, x will be unchanged,
# it will be the same as outputs[-1]. Otherwise it will be concatenated
# from different pieces of 'outputs', taking each dimension from the
# most recent output that has it present.
x = self._get_full_dim_output(outputs)
x = self.downsample_output(x)
# class Downsample has this rounding behavior..
assert self.output_downsampling_factor == 2
if torch.jit.is_scripting() or torch.jit.is_tracing():
lengths = (x_lens + 1) // 2
else:
with warnings.catch_warnings():
warnings.simplefilter("ignore")
lengths = (x_lens + 1) // 2
return x, lengths, new_states
@torch.jit.export
def get_init_states(
self,
batch_size: int = 1,
device: torch.device = torch.device("cpu"),
) -> List[Tensor]:
"""Get initial states.
A list of cached tensors of all encoder layers. For layer-i, states[i*6:(i+1)*6]
is (cached_key, cached_nonlin_attn, cached_val1, cached_val2, cached_conv1, cached_conv2).
"""
states = []
for i, module in enumerate(self.encoders):
num_layers = module.num_layers
embed_dim = self.encoder_dim[i]
ds = self.downsampling_factor[i]
num_heads = self.num_heads[i]
key_dim = self.query_head_dim[i] * num_heads
value_dim = self.value_head_dim[i] * num_heads
downsample_left = self.left_context_frames[0] // ds
nonlin_attn_head_dim = 3 * embed_dim // 4
conv_left_pad = self.cnn_module_kernel[i] // 2
for layer in range(num_layers):
cached_key = torch.zeros(downsample_left, batch_size, key_dim).to(
device
)
cached_nonlin_attn = torch.zeros(
1, batch_size, downsample_left, nonlin_attn_head_dim
).to(device)
cached_val1 = torch.zeros(downsample_left, batch_size, value_dim).to(
device
)
cached_val2 = torch.zeros(downsample_left, batch_size, value_dim).to(
device
)
cached_conv1 = torch.zeros(batch_size, embed_dim, conv_left_pad).to(
device
)
cached_conv2 = torch.zeros(batch_size, embed_dim, conv_left_pad).to(
device
)
states += [
cached_key,
cached_nonlin_attn,
cached_val1,
cached_val2,
cached_conv1,
cached_conv2,
]
return states
def _whitening_schedule(x: float, ratio: float = 2.0) -> ScheduledFloat:
return ScheduledFloat((0.0, x), (20000.0, ratio * x), default=x)
def _balancer_schedule(min_prob: float):
return ScheduledFloat((0.0, 0.4), (8000.0, min_prob))
class Zipformer2EncoderLayer(nn.Module):
"""
Args:
embed_dim: the number of expected features in the input (required).
nhead: the number of heads in the multiheadattention models (required).
feedforward_dim: the dimension of the feedforward network model (default=2048).
dropout: the dropout value (default=0.1).
cnn_module_kernel (int): Kernel size of convolution module.
Examples::
>>> encoder_layer = Zipformer2EncoderLayer(embed_dim=512, nhead=8)
>>> src = torch.rand(10, 32, 512)
>>> pos_emb = torch.rand(32, 19, 512)
>>> out = encoder_layer(src, pos_emb)
"""
def __init__(
self,
embed_dim: int,
pos_dim: int,
num_heads: int,
query_head_dim: int,
pos_head_dim: int,
value_head_dim: int,
feedforward_dim: int,
dropout: FloatLike = 0.1,
cnn_module_kernel: int = 31,
causal: bool = False,
attention_skip_rate: FloatLike = ScheduledFloat(
(0.0, 0.2), (4000.0, 0.05), (16000, 0.0), default=0
),
conv_skip_rate: FloatLike = ScheduledFloat(
(0.0, 0.2), (4000.0, 0.05), (16000, 0.0), default=0
),
const_attention_rate: FloatLike = ScheduledFloat(
(0.0, 0.25), (4000.0, 0.025), default=0
),
ff2_skip_rate: FloatLike = ScheduledFloat(
(0.0, 0.1), (4000.0, 0.01), (50000.0, 0.0)
),
ff3_skip_rate: FloatLike = ScheduledFloat(
(0.0, 0.1), (4000.0, 0.01), (50000.0, 0.0)
),
bypass_skip_rate: FloatLike = ScheduledFloat(
(0.0, 0.5), (4000.0, 0.02), default=0
),
) -> None:
super(Zipformer2EncoderLayer, self).__init__()
self.embed_dim = embed_dim
# self.bypass implements layer skipping as well as bypass; see its default values.
self.bypass = BypassModule(
embed_dim, skip_rate=bypass_skip_rate, straight_through_rate=0
)
# bypass_mid is bypass used in the middle of the layer.
self.bypass_mid = BypassModule(embed_dim, straight_through_rate=0)
# skip probability for dynamic modules (meaning: anything but feedforward).
self.attention_skip_rate = copy.deepcopy(attention_skip_rate)
# an additional skip probability that applies to ConvModule to stop it from
# contributing too much early on.
self.conv_skip_rate = copy.deepcopy(conv_skip_rate)
# ff2_skip_rate is to prevent the ff2 module from having output that's too big
# compared to its residual.
self.ff2_skip_rate = copy.deepcopy(ff2_skip_rate)
self.ff3_skip_rate = copy.deepcopy(ff3_skip_rate)
self.const_attention_rate = copy.deepcopy(const_attention_rate)
self.self_attn_weights = RelPositionMultiheadAttentionWeights(
embed_dim,
pos_dim=pos_dim,
num_heads=num_heads,
query_head_dim=query_head_dim,
pos_head_dim=pos_head_dim,
dropout=0.0,
)
self.self_attn1 = SelfAttention(embed_dim, num_heads, value_head_dim)
self.self_attn2 = SelfAttention(embed_dim, num_heads, value_head_dim)
self.feed_forward1 = FeedforwardModule(
embed_dim, (feedforward_dim * 3) // 4, dropout
)
self.feed_forward2 = FeedforwardModule(embed_dim, feedforward_dim, dropout)
self.feed_forward3 = FeedforwardModule(
embed_dim, (feedforward_dim * 5) // 4, dropout
)
self.nonlin_attention = NonlinAttention(
embed_dim, hidden_channels=3 * embed_dim // 4
)
self.conv_module1 = ConvolutionModule(
embed_dim, cnn_module_kernel, causal=causal
)
self.conv_module2 = ConvolutionModule(
embed_dim, cnn_module_kernel, causal=causal
)
# TODO: remove it
self.bypass_scale = nn.Parameter(torch.full((embed_dim,), 0.5))
self.norm = BiasNorm(embed_dim)
self.balancer1 = Balancer(
embed_dim,
channel_dim=-1,
min_positive=0.45,
max_positive=0.55,
min_abs=0.2,
max_abs=4.0,
)
# balancer for output of NonlinAttentionModule
self.balancer_na = Balancer(
embed_dim,
channel_dim=-1,
min_positive=0.3,
max_positive=0.7,
min_abs=ScheduledFloat((0.0, 0.004), (4000.0, 0.02)),
prob=0.05, # out of concern for memory usage
)
# balancer for output of feedforward2, prevent it from staying too
# small. give this a very small probability, even at the start of
# training, it's to fix a rare problem and it's OK to fix it slowly.
self.balancer_ff2 = Balancer(
embed_dim,
channel_dim=-1,
min_positive=0.3,
max_positive=0.7,
min_abs=ScheduledFloat((0.0, 0.0), (4000.0, 0.1), default=0.0),
max_abs=2.0,
prob=0.05,
)
self.balancer_ff3 = Balancer(
embed_dim,
channel_dim=-1,
min_positive=0.3,
max_positive=0.7,
min_abs=ScheduledFloat((0.0, 0.0), (4000.0, 0.2), default=0.0),
max_abs=4.0,
prob=0.05,
)
self.whiten = Whiten(
num_groups=1,
whitening_limit=_whitening_schedule(4.0, ratio=3.0),
prob=(0.025, 0.25),
grad_scale=0.01,
)
self.balancer2 = Balancer(
embed_dim,
channel_dim=-1,
min_positive=0.45,
max_positive=0.55,
min_abs=0.1,
max_abs=4.0,
)
def get_sequence_dropout_mask(
self, x: Tensor, dropout_rate: float
) -> Optional[Tensor]:
if (
dropout_rate == 0.0
or not self.training
or torch.jit.is_scripting()
or torch.jit.is_tracing()
):
return None
batch_size = x.shape[1]
mask = (torch.rand(batch_size, 1, device=x.device) > dropout_rate).to(x.dtype)
return mask
def sequence_dropout(self, x: Tensor, dropout_rate: float) -> Tensor:
"""
Apply sequence-level dropout to x.
x shape: (seq_len, batch_size, embed_dim)
"""
dropout_mask = self.get_sequence_dropout_mask(x, dropout_rate)
if dropout_mask is None:
return x
else:
return x * dropout_mask
def forward(
self,
src: Tensor,
pos_emb: Tensor,
chunk_size: int = -1,
attn_mask: Optional[Tensor] = None,
src_key_padding_mask: Optional[Tensor] = None,
) -> Tensor:
"""
Pass the input through the encoder layer.
Args:
src: the sequence to the encoder (required): shape (seq_len, batch_size, embedding_dim).
pos_emb: (1, 2*seq_len-1, pos_emb_dim) or (batch_size, 2*seq_len-1, pos_emb_dim)
chunk_size: the number of frames per chunk, of >= 0; if -1, no chunking.
feature_mask: something that broadcasts with src, that we'll multiply `src`
by at every layer: if a Tensor, likely of shape (seq_len, batch_size, embedding_dim)
attn_mask: the attention mask, of shape (batch_size, seq_len, seq_len) or (seq_len, seq_len),
interpreted as (batch_size, tgt_seq_len, src_seq_len) or (tgt_seq_len, src_seq_len).
True means masked position. May be None.
src_key_padding_mask: the mask for padding, of shape (batch_size, seq_len); True means
masked position. May be None.
Returns:
A tensor which has the same shape as src
"""
src_orig = src
# dropout rate for non-feedforward submodules
if torch.jit.is_scripting() or torch.jit.is_tracing():
attention_skip_rate = 0.0
else:
attention_skip_rate = (
float(self.attention_skip_rate) if self.training else 0.0
)
# attn_weights: (num_heads, batch_size, seq_len, seq_len)
attn_weights = self.self_attn_weights(
src,
pos_emb=pos_emb,
attn_mask=attn_mask,
key_padding_mask=src_key_padding_mask,
)
src = src + self.feed_forward1(src)
self_attn_dropout_mask = self.get_sequence_dropout_mask(
src, attention_skip_rate
)
selected_attn_weights = attn_weights[0:1]
if torch.jit.is_scripting() or torch.jit.is_tracing():
pass
elif not self.training and random.random() < float(self.const_attention_rate):
# Make attention weights constant. The intention is to
# encourage these modules to do something similar to an
# averaging-over-time operation.
# only need the mask, can just use the 1st one and expand later
selected_attn_weights = selected_attn_weights[0:1]
selected_attn_weights = (selected_attn_weights > 0.0).to(
selected_attn_weights.dtype
)
selected_attn_weights = selected_attn_weights * (
1.0 / selected_attn_weights.sum(dim=-1, keepdim=True)
)
na = self.balancer_na(self.nonlin_attention(src, selected_attn_weights))
src = src + (
na if self_attn_dropout_mask is None else na * self_attn_dropout_mask
)
self_attn = self.self_attn1(src, attn_weights)
src = src + (
self_attn
if self_attn_dropout_mask is None
else self_attn * self_attn_dropout_mask
)
if torch.jit.is_scripting() or torch.jit.is_tracing():
conv_skip_rate = 0.0
else:
conv_skip_rate = float(self.conv_skip_rate) if self.training else 0.0
src = src + self.sequence_dropout(
self.conv_module1(
src, chunk_size=chunk_size, src_key_padding_mask=src_key_padding_mask
),
conv_skip_rate,
)
if torch.jit.is_scripting() or torch.jit.is_tracing():
ff2_skip_rate = 0.0
else:
ff2_skip_rate = float(self.ff2_skip_rate) if self.training else 0.0
src = src + self.sequence_dropout(
self.balancer_ff2(self.feed_forward2(src)), ff2_skip_rate
)
# bypass in the middle of the layer.
src = self.bypass_mid(src_orig, src)
self_attn = self.self_attn2(src, attn_weights)
src = src + (
self_attn
if self_attn_dropout_mask is None
else self_attn * self_attn_dropout_mask
)
if torch.jit.is_scripting() or torch.jit.is_tracing():
conv_skip_rate = 0.0
else:
conv_skip_rate = float(self.conv_skip_rate) if self.training else 0.0
src = src + self.sequence_dropout(
self.conv_module2(
src, chunk_size=chunk_size, src_key_padding_mask=src_key_padding_mask
),
conv_skip_rate,
)
if torch.jit.is_scripting() or torch.jit.is_tracing():
ff3_skip_rate = 0.0
else:
ff3_skip_rate = float(self.ff3_skip_rate) if self.training else 0.0
src = src + self.sequence_dropout(
self.balancer_ff3(self.feed_forward3(src)), ff3_skip_rate
)
src = self.balancer1(src)
src = self.norm(src)
src = self.bypass(src_orig, src)
src = self.balancer2(src)
src = self.whiten(src)
return src
def streaming_forward(
self,
src: Tensor,
pos_emb: Tensor,
cached_key: Tensor,
cached_nonlin_attn: Tensor,
cached_val1: Tensor,
cached_val2: Tensor,
cached_conv1: Tensor,
cached_conv2: Tensor,
left_context_len: int,
src_key_padding_mask: Tensor,
) -> Tuple[Tensor, Tensor, Tensor, Tensor, Tensor, Tensor, Tensor]:
"""Pass the input through the encoder layer in streaming forward mode.
Args:
src: the sequence to the encoder (required): shape (seq_len, batch_size, embedding_dim).
pos_emb: (1, left_context_len+2*seq_len-1, pos_emb_dim) or
(batch_size, left_context_len+2*seq_len-1, pos_emb_dim)
cached_key: cached attention key tensor of left context,
of shape (left_context_len, batch_size, key_dim)
cached_nonlin_attn: left context for nonlin_attention module, a Tensor of shape
(num_heads, batch_size, left_context_len, head_dim)
cached_val1: cached left context for the first attention module,
of shape (left_context_len, batch_size, value_dim)
cached_val2: cached left context for the second attention module,
of shape (left_context_len, batch_size, value_dim)
cached_conv1: cached left context for the first convolution module,
of shape (batch_size, channels, left_pad)
cached_conv2: cached left context for the second convolution module,
of shape (batch_size, channels, left_pad)
left_context_len: number of left context frames.
src_key_padding_mask: the mask for padding, of shape
(batch_size, left_context_len + seq_len); True means masked position.
May be None.
Returns:
- x, with the same shape as src
- updated cached_key
- updated cached_nonlin_attn
- updated cached_val1
- updated cached_val2
- updated cached_conv1
- updated cached_conv2
"""
src_orig = src
# attn_weights: (num_heads, batch_size, seq_len, seq_len)
attn_weights, cached_key = self.self_attn_weights.streaming_forward(
src,
pos_emb=pos_emb,
cached_key=cached_key,
left_context_len=left_context_len,
key_padding_mask=src_key_padding_mask,
)
src = src + self.feed_forward1(src)
na, cached_nonlin_attn = self.nonlin_attention.streaming_forward(
src,
attn_weights[0:1],
cached_x=cached_nonlin_attn,
left_context_len=left_context_len,
)
src = src + na
self_attn, cached_val1 = self.self_attn1.streaming_forward(
src,
attn_weights=attn_weights,
cached_val=cached_val1,
left_context_len=left_context_len,
)
src = src + self_attn
src_conv, cached_conv1 = self.conv_module1.streaming_forward(
src,
cache=cached_conv1,
src_key_padding_mask=src_key_padding_mask[:, left_context_len:],
)
src = src + src_conv
src = src + self.feed_forward2(src)
# bypass in the middle of the layer.
src = self.bypass_mid(src_orig, src)
self_attn, cached_val2 = self.self_attn2.streaming_forward(
src,
attn_weights=attn_weights,
cached_val=cached_val2,
left_context_len=left_context_len,
)
src = src + self_attn
src_conv, cached_conv2 = self.conv_module2.streaming_forward(
src,
cache=cached_conv2,
src_key_padding_mask=src_key_padding_mask[:, left_context_len:],
)
src = src + src_conv
src = src + self.feed_forward3(src)
src = self.norm(src)
src = self.bypass(src_orig, src)
return (
src,
cached_key,
cached_nonlin_attn,
cached_val1,
cached_val2,
cached_conv1,
cached_conv2,
)
class Zipformer2Encoder(nn.Module):
r"""Zipformer2Encoder is a stack of N encoder layers
Args:
encoder_layer: an instance of the Zipformer2EncoderLayer() class (required).
num_layers: the number of sub-encoder-layers in the encoder (required).
pos_dim: the dimension for the relative positional encoding
Examples::
>>> encoder_layer = Zipformer2EncoderLayer(embed_dim=512, nhead=8)
>>> zipformer_encoder = Zipformer2Encoder(encoder_layer, num_layers=6)
>>> src = torch.rand(10, 32, 512)
>>> out = zipformer_encoder(src)
"""
def __init__(
self,
encoder_layer: nn.Module,
num_layers: int,
pos_dim: int,
dropout: float,
warmup_begin: float,
warmup_end: float,
initial_layerdrop_rate: float = 0.5,
final_layerdrop_rate: float = 0.05,
) -> None:
super().__init__()
self.encoder_pos = CompactRelPositionalEncoding(
pos_dim, dropout_rate=0.15, length_factor=1.0
)
self.layers = nn.ModuleList(
[copy.deepcopy(encoder_layer) for i in range(num_layers)]
)
self.num_layers = num_layers
assert 0 <= warmup_begin <= warmup_end
delta = (1.0 / num_layers) * (warmup_end - warmup_begin)
cur_begin = warmup_begin # interpreted as a training batch index
for i in range(num_layers):
cur_end = cur_begin + delta
self.layers[i].bypass.skip_rate = ScheduledFloat(
(cur_begin, initial_layerdrop_rate),
(cur_end, final_layerdrop_rate),
default=0.0,
)
cur_begin = cur_end
def forward(
self,
src: Tensor,
chunk_size: int = -1,
feature_mask: Union[Tensor, float] = 1.0,
attn_mask: Optional[Tensor] = None,
src_key_padding_mask: Optional[Tensor] = None,
) -> Tensor:
r"""Pass the input through the encoder layers in turn.
Args:
src: the sequence to the encoder (required): shape (seq_len, batch_size, embedding_dim).
chunk_size: the number of frames per chunk, of >= 0; if -1, no chunking.
feature_mask: something that broadcasts with src, that we'll multiply `src`
by at every layer: if a Tensor, likely of shape (seq_len, batch_size, embedding_dim)
attn_mask: the attention mask, of shape (batch_size, seq_len, seq_len) or (seq_len, seq_len),
interpreted as (batch_size, tgt_seq_len, src_seq_len) or (tgt_seq_len, src_seq_len).
True means masked position. May be None.
src_key_padding_mask: the mask for padding, of shape (batch_size, seq_len); True means
masked position. May be None.
Returns: a Tensor with the same shape as src.
"""
pos_emb = self.encoder_pos(src)
output = src
if not torch.jit.is_scripting() and not torch.jit.is_tracing():
output = output * feature_mask
for i, mod in enumerate(self.layers):
output = mod(
output,
pos_emb,
chunk_size=chunk_size,
attn_mask=attn_mask,
src_key_padding_mask=src_key_padding_mask,
)
if not torch.jit.is_scripting() and not torch.jit.is_tracing():
output = output * feature_mask
return output
def streaming_forward(
self,
src: Tensor,
states: List[Tensor],
left_context_len: int,
src_key_padding_mask: Tensor,
) -> Tuple[Tensor, List[Tensor]]:
r"""Pass the input through the encoder layers in turn.
Args:
src: the sequence to the encoder (required): shape (seq_len, batch_size, embedding_dim).
states: list of cached tensors of N encoder layers. For layer-i, states[i*6:(i+1)*6] is
(cached_key, cached_nonlin_attn, cached_val1, cached_val2, cached_conv1, cached_conv2).
left_context_len: Number of left context frames.
src_key_padding_mask: the mask for padding, of shape
(batch_size, left_context_len + seq_len); True means masked position.
May be None.
Returns:
- output, a Tensor with the same shape as src.
- updated states
"""
pos_emb = self.encoder_pos(src, left_context_len)
output = src
new_states = []
for i, mod in enumerate(self.layers):
(
cached_key,
cached_nonlin_attn,
cached_val1,
cached_val2,
cached_conv1,
cached_conv2,
) = states[i * 6 : (i + 1) * 6]
(
output,
new_cached_key,
new_cached_nonlin_attn,
new_cached_val1,
new_cached_val2,
new_cached_conv1,
new_cached_conv2,
) = mod.streaming_forward(
output,
pos_emb,
cached_key=cached_key,
cached_nonlin_attn=cached_nonlin_attn,
cached_val1=cached_val1,
cached_val2=cached_val2,
cached_conv1=cached_conv1,
cached_conv2=cached_conv2,
left_context_len=left_context_len,
src_key_padding_mask=src_key_padding_mask,
)
new_states += [
new_cached_key,
new_cached_nonlin_attn,
new_cached_val1,
new_cached_val2,
new_cached_conv1,
new_cached_conv2,
]
return output, new_states
class BypassModule(nn.Module):
"""
An nn.Module that implements a learnable bypass scale, and also randomized per-sequence
layer-skipping. The bypass is limited during early stages of training to be close to
"straight-through", i.e. to not do the bypass operation much initially, in order to
force all the modules to learn something.
"""
def __init__(
self,
embed_dim: int,
skip_rate: FloatLike = 0.0,
straight_through_rate: FloatLike = 0.0,
scale_min: FloatLike = ScheduledFloat((0.0, 0.9), (20000.0, 0.2), default=0),
scale_max: FloatLike = 1.0,
):
super().__init__()
self.bypass_scale = nn.Parameter(torch.full((embed_dim,), 0.5))
self.skip_rate = copy.deepcopy(skip_rate)
self.straight_through_rate = copy.deepcopy(straight_through_rate)
self.scale_min = copy.deepcopy(scale_min)
self.scale_max = copy.deepcopy(scale_max)
def _get_bypass_scale(self, batch_size: int):
# returns bypass-scale of shape (num_channels,),
# or (batch_size, num_channels,). This is actually the
# scale on the non-residual term, so 0 correponds to bypassing
# this module.
if torch.jit.is_scripting() or torch.jit.is_tracing() or not self.training:
return self.bypass_scale
else:
ans = limit_param_value(
self.bypass_scale, min=float(self.scale_min), max=float(self.scale_max)
)
skip_rate = float(self.skip_rate)
if skip_rate != 0.0:
mask = torch.rand((batch_size, 1), device=ans.device) > skip_rate
ans = ans * mask
# now ans is of shape (batch_size, num_channels), and is zero for sequences
# on which we have randomly chosen to do layer-skipping.
straight_through_rate = float(self.straight_through_rate)
if straight_through_rate != 0.0:
mask = (
torch.rand((batch_size, 1), device=ans.device)
< straight_through_rate
)
ans = torch.maximum(ans, mask.to(ans.dtype))
return ans
def forward(self, src_orig: Tensor, src: Tensor):
"""
Args: src_orig and src are both of shape (seq_len, batch_size, num_channels)
Returns: something with the same shape as src and src_orig
"""
bypass_scale = self._get_bypass_scale(src.shape[1])
return src_orig + (src - src_orig) * bypass_scale
class DownsampledZipformer2Encoder(nn.Module):
r"""
DownsampledZipformer2Encoder is a zipformer encoder evaluated at a reduced frame rate,
after convolutional downsampling, and then upsampled again at the output, and combined
with the origin input, so that the output has the same shape as the input.
"""
def __init__(
self, encoder: nn.Module, dim: int, downsample: int, dropout: FloatLike
):
super(DownsampledZipformer2Encoder, self).__init__()
self.downsample_factor = downsample
self.downsample = SimpleDownsample(dim, downsample, dropout)
self.num_layers = encoder.num_layers
self.encoder = encoder
self.upsample = SimpleUpsample(dim, downsample)
self.out_combiner = BypassModule(dim, straight_through_rate=0)
def forward(
self,
src: Tensor,
chunk_size: int = -1,
feature_mask: Union[Tensor, float] = 1.0,
attn_mask: Optional[Tensor] = None,
src_key_padding_mask: Optional[Tensor] = None,
) -> Tensor:
r"""Downsample, go through encoder, upsample.
Args:
src: the sequence to the encoder (required): shape (seq_len, batch_size, embedding_dim).
feature_mask: something that broadcasts with src, that we'll multiply `src`
by at every layer: if a Tensor, likely of shape (seq_len, batch_size, embedding_dim)
attn_mask: the attention mask, of shape (batch_size, seq_len, seq_len) or (seq_len, seq_len),
interpreted as (batch_size, tgt_seq_len, src_seq_len) or (tgt_seq_len, src_seq_len).
True means masked position. May be None.
src_key_padding_mask: the mask for padding, of shape (batch_size, seq_len); True means
masked position. May be None.
Returns: a Tensor with the same shape as src.
"""
src_orig = src
src = self.downsample(src)
ds = self.downsample_factor
if attn_mask is not None:
attn_mask = attn_mask[::ds, ::ds]
src = self.encoder(
src,
chunk_size=chunk_size // ds,
feature_mask=feature_mask,
attn_mask=attn_mask,
src_key_padding_mask=src_key_padding_mask,
)
src = self.upsample(src)
# remove any extra frames that are not a multiple of downsample_factor
src = src[: src_orig.shape[0]]
return self.out_combiner(src_orig, src)
def streaming_forward(
self,
src: Tensor,
states: List[Tensor],
left_context_len: int,
src_key_padding_mask: Tensor,
) -> Tuple[Tensor, List[Tensor]]:
r"""Downsample, go through encoder, upsample, in streaming forward mode.
Args:
src: the sequence to the encoder (required): shape (seq_len, batch_size, embedding_dim).
states: list of cached tensors of N encoder layers. For layer-i, states[i*6:(i+1)*6] is
(cached_key, cached_nonlin_attn, cached_val1, cached_val2, cached_conv1, cached_conv2).
left_context_len: Number of left context frames.
src_key_padding_mask: the mask for padding, of shape (batch_size, left_context_len+seq_len);
True means masked position. May be None.
Returns:
- output, a Tensor with the same shape as src.
- updated states
"""
src_orig = src
src = self.downsample(src)
src, new_states = self.encoder.streaming_forward(
src,
states=states,
left_context_len=left_context_len,
src_key_padding_mask=src_key_padding_mask,
)
src = self.upsample(src)
# remove any extra frames that are not a multiple of downsample_factor
src = src[: src_orig.shape[0]]
return self.out_combiner(src_orig, src), new_states
class SimpleDownsample(torch.nn.Module):
"""
Does downsampling with attention, by weighted sum, and a projection..
"""
def __init__(self, channels: int, downsample: int, dropout: FloatLike):
super(SimpleDownsample, self).__init__()
self.bias = nn.Parameter(torch.zeros(downsample))
self.name = None # will be set from training code
self.dropout = copy.deepcopy(dropout)
self.downsample = downsample
def forward(self, src: Tensor) -> Tensor:
"""
x: (seq_len, batch_size, in_channels)
Returns a tensor of shape
( (seq_len+downsample-1)//downsample, batch_size, channels)
"""
(seq_len, batch_size, in_channels) = src.shape
ds = self.downsample
d_seq_len = (seq_len + ds - 1) // ds
# Pad to an exact multiple of self.downsample
# right-pad src, repeating the last element.
pad = d_seq_len * ds - seq_len
src_extra = src[src.shape[0] - 1 :].expand(pad, src.shape[1], src.shape[2])
src = torch.cat((src, src_extra), dim=0)
assert src.shape[0] == d_seq_len * ds
src = src.reshape(d_seq_len, ds, batch_size, in_channels)
weights = self.bias.softmax(dim=0)
# weights: (downsample, 1, 1)
weights = weights.unsqueeze(-1).unsqueeze(-1)
# ans1 is the first `in_channels` channels of the output
ans = (src * weights).sum(dim=1)
return ans
class SimpleUpsample(torch.nn.Module):
"""
A very simple form of upsampling that mostly just repeats the input, but
also adds a position-specific bias.
"""
def __init__(self, num_channels: int, upsample: int):
super(SimpleUpsample, self).__init__()
self.upsample = upsample
def forward(self, src: Tensor) -> Tensor:
"""
x: (seq_len, batch_size, num_channels)
Returns a tensor of shape
( (seq_len*upsample), batch_size, num_channels)
"""
upsample = self.upsample
(seq_len, batch_size, num_channels) = src.shape
src = src.unsqueeze(1).expand(seq_len, upsample, batch_size, num_channels)
src = src.reshape(seq_len * upsample, batch_size, num_channels)
return src
class CompactRelPositionalEncoding(torch.nn.Module):
"""
Relative positional encoding module. This version is "compact" meaning it is able to encode
the important information about the relative position in a relatively small number of dimensions.
The goal is to make it so that small differences between large relative offsets (e.g. 1000 vs. 1001)
make very little difference to the embedding. Such differences were potentially important
when encoding absolute position, but not important when encoding relative position because there
is now no need to compare two large offsets with each other.
Our embedding works done by projecting the interval [-infinity,infinity] to a finite interval
using the atan() function, before doing the fourier transform of that fixed interval. The
atan() function would compress the "long tails" too small,
making it hard to distinguish between different magnitudes of large offsets, so we use a logarithmic
function to compress large offsets to a smaller range before applying atan().
Scalings are chosen in such a way that the embedding can clearly distinguish invidual offsets as long
as they are quite close to the origin, e.g. abs(offset) <= about sqrt(embedding_dim)
Args:
embed_dim: Embedding dimension.
dropout_rate: Dropout rate.
max_len: Maximum input length: just a heuristic for initialization.
length_factor: a heuristic scale (should be >= 1.0) which, if larger, gives
less weight to small differences of offset near the origin.
"""
def __init__(
self,
embed_dim: int,
dropout_rate: FloatLike,
max_len: int = 1000,
length_factor: float = 1.0,
) -> None:
"""Construct a CompactRelPositionalEncoding object."""
super(CompactRelPositionalEncoding, self).__init__()
self.embed_dim = embed_dim
assert embed_dim % 2 == 0
self.dropout = Dropout2(dropout_rate)
self.pe = None
assert length_factor >= 1.0
self.length_factor = length_factor
self.extend_pe(torch.tensor(0.0).expand(max_len))
def extend_pe(self, x: Tensor, left_context_len: int = 0) -> None:
"""Reset the positional encodings."""
T = x.size(0) + left_context_len
if self.pe is not None:
# self.pe contains both positive and negative parts
# the length of self.pe is 2 * input_len - 1
if self.pe.size(0) >= T * 2 - 1:
self.pe = self.pe.to(dtype=x.dtype, device=x.device)
return
# if T == 4, x would contain [ -3, -2, 1, 0, 1, 2, 3 ]
x = torch.arange(-(T - 1), T, device=x.device).to(torch.float32).unsqueeze(1)
freqs = 1 + torch.arange(self.embed_dim // 2, device=x.device)
# `compression_length` this is arbitrary/heuristic, if it is larger we have more resolution
# for small time offsets but less resolution for large time offsets.
compression_length = self.embed_dim**0.5
# x_compressed, like X, goes from -infinity to infinity as T goes from -infinity to infinity;
# but it does so more slowly than T for large absolute values of T.
# The formula is chosen so that d(x_compressed )/dx is 1 around x == 0, which
# is important.
x_compressed = (
compression_length
* x.sign()
* ((x.abs() + compression_length).log() - math.log(compression_length))
)
# if self.length_factor == 1.0, then length_scale is chosen so that the
# FFT can exactly separate points close to the origin (T == 0). So this
# part of the formulation is not really heuristic.
# But empirically, for ASR at least, length_factor > 1.0 seems to work better.
length_scale = self.length_factor * self.embed_dim / (2.0 * math.pi)
# note for machine implementations: if atan is not available, we can use:
# x.sign() * ((1 / (x.abs() + 1)) - 1) * (-math.pi/2)
# check on wolframalpha.com: plot(sign(x) * (1 / ( abs(x) + 1) - 1 ) * -pi/2 , atan(x))
x_atan = (x_compressed / length_scale).atan() # results between -pi and pi
cosines = (x_atan * freqs).cos()
sines = (x_atan * freqs).sin()
pe = torch.zeros(x.shape[0], self.embed_dim, device=x.device)
pe[:, 0::2] = cosines
pe[:, 1::2] = sines
pe[:, -1] = 1.0 # for bias.
self.pe = pe.to(dtype=x.dtype)
def forward(self, x: Tensor, left_context_len: int = 0) -> Tensor:
"""Create positional encoding.
Args:
x (Tensor): Input tensor (time, batch, `*`).
left_context_len: (int): Length of cached left context.
Returns:
positional embedding, of shape (batch, left_context_len + 2*time-1, `*`).
"""
self.extend_pe(x, left_context_len)
x_size_left = x.size(0) + left_context_len
# length of positive side: x.size(0) + left_context_len
# length of negative side: x.size(0)
pos_emb = self.pe[
self.pe.size(0) // 2
- x_size_left
+ 1 : self.pe.size(0) // 2 # noqa E203
+ x.size(0),
:,
]
pos_emb = pos_emb.unsqueeze(0)
return self.dropout(pos_emb)
class RelPositionMultiheadAttentionWeights(nn.Module):
r"""Module that computes multi-head attention weights with relative position encoding.
Various other modules consume the resulting attention weights: see, for example, the
SimpleAttention module which allows you to compute conventional attention.
This is a quite heavily modified from: "Transformer-XL: Attentive Language Models Beyond a Fixed-Length Context",
we have to write up the differences.
Args:
embed_dim: number of channels at the input to this module, e.g. 256
pos_dim: dimension of the positional encoding vectors, e.g. 128.
num_heads: number of heads to compute weights for, e.g. 8
query_head_dim: dimension of the query (and key), per head. e.g. 24.
pos_head_dim: dimension of the projected positional encoding per head, e.g. 4.
dropout: dropout probability for attn_output_weights. Default: 0.0.
pos_emb_skip_rate: probability for skipping the pos_emb part of the scores on
any given call to forward(), in training time.
"""
def __init__(
self,
embed_dim: int,
pos_dim: int,
num_heads: int,
query_head_dim: int,
pos_head_dim: int,
dropout: float = 0.0,
pos_emb_skip_rate: FloatLike = ScheduledFloat((0.0, 0.5), (4000.0, 0.0)),
) -> None:
super().__init__()
self.embed_dim = embed_dim
self.num_heads = num_heads
self.query_head_dim = query_head_dim
self.pos_head_dim = pos_head_dim
self.dropout = dropout
self.pos_emb_skip_rate = copy.deepcopy(pos_emb_skip_rate)
self.name = None # will be overwritten in training code; for diagnostics.
key_head_dim = query_head_dim
in_proj_dim = (query_head_dim + key_head_dim + pos_head_dim) * num_heads
# the initial_scale is supposed to take over the "scaling" factor of
# head_dim ** -0.5 that has been used in previous forms of attention,
# dividing it between the query and key. Note: this module is intended
# to be used with the ScaledAdam optimizer; with most other optimizers,
# it would be necessary to apply the scaling factor in the forward function.
self.in_proj = ScaledLinear(
embed_dim, in_proj_dim, bias=True, initial_scale=query_head_dim**-0.25
)
self.whiten_keys = Whiten(
num_groups=num_heads,
whitening_limit=_whitening_schedule(3.0),
prob=(0.025, 0.25),
grad_scale=0.025,
)
# add a balancer for the keys that runs with very small probability, and
# tries to enforce that all dimensions have mean around zero. The
# weights produced by this module are invariant to adding a constant to
# the keys, so the derivative of the bias is mathematically zero; but
# due to how Adam/ScaledAdam work, it can learn a fairly large nonzero
# bias because the small numerical roundoff tends to have a non-random
# sign. This module is intended to prevent that. Use a very small
# probability; that should be suffixient to fix the problem.
self.balance_keys = Balancer(
key_head_dim * num_heads,
channel_dim=-1,
min_positive=0.4,
max_positive=0.6,
min_abs=0.0,
max_abs=100.0,
prob=0.025,
)
# linear transformation for positional encoding.
self.linear_pos = ScaledLinear(
pos_dim, num_heads * pos_head_dim, bias=False, initial_scale=0.05
)
# the following are for diagnosics only, see --print-diagnostics option
self.copy_pos_query = Identity()
self.copy_query = Identity()
def forward(
self,
x: Tensor,
pos_emb: Tensor,
key_padding_mask: Optional[Tensor] = None,
attn_mask: Optional[Tensor] = None,
) -> Tensor:
r"""
Args:
x: input of shape (seq_len, batch_size, embed_dim)
pos_emb: Positional embedding tensor, of shape (1, 2*seq_len - 1, pos_dim)
key_padding_mask: a bool tensor of shape (batch_size, seq_len). Positions that
are True in this mask will be ignored as sources in the attention weighting.
attn_mask: mask of shape (seq_len, seq_len) or (batch_size, seq_len, seq_len),
interpreted as ([batch_size,] tgt_seq_len, src_seq_len)
saying which positions are allowed to attend to which other positions.
Returns:
a tensor of attention weights, of shape (hum_heads, batch_size, seq_len, seq_len)
interpreted as (hum_heads, batch_size, tgt_seq_len, src_seq_len).
"""
x = self.in_proj(x)
query_head_dim = self.query_head_dim
pos_head_dim = self.pos_head_dim
num_heads = self.num_heads
seq_len, batch_size, _ = x.shape
query_dim = query_head_dim * num_heads
# self-attention
q = x[..., 0:query_dim]
k = x[..., query_dim : 2 * query_dim]
# p is the position-encoding query
p = x[..., 2 * query_dim :]
assert p.shape[-1] == num_heads * pos_head_dim
q = self.copy_query(q) # for diagnostics only, does nothing.
k = self.whiten_keys(self.balance_keys(k)) # does nothing in the forward pass.
p = self.copy_pos_query(p) # for diagnostics only, does nothing.
q = q.reshape(seq_len, batch_size, num_heads, query_head_dim)
p = p.reshape(seq_len, batch_size, num_heads, pos_head_dim)
k = k.reshape(seq_len, batch_size, num_heads, query_head_dim)
# time1 refers to target, time2 refers to source.
q = q.permute(2, 1, 0, 3) # (head, batch, time1, query_head_dim)
p = p.permute(2, 1, 0, 3) # (head, batch, time1, pos_head_dim)
k = k.permute(2, 1, 3, 0) # (head, batch, d_k, time2)
attn_scores = torch.matmul(q, k)
use_pos_scores = False
if torch.jit.is_scripting() or torch.jit.is_tracing():
# We can't put random.random() in the same line
use_pos_scores = True
elif not self.training or random.random() >= float(self.pos_emb_skip_rate):
use_pos_scores = True
if use_pos_scores:
pos_emb = self.linear_pos(pos_emb)
seq_len2 = 2 * seq_len - 1
pos_emb = pos_emb.reshape(-1, seq_len2, num_heads, pos_head_dim).permute(
2, 0, 3, 1
)
# pos shape now: (head, {1 or batch_size}, pos_dim, seq_len2)
# (head, batch, time1, pos_dim) x (head, 1, pos_dim, seq_len2) -> (head, batch, time1, seq_len2)
# [where seq_len2 represents relative position.]
pos_scores = torch.matmul(p, pos_emb)
# the following .as_strided() expression converts the last axis of pos_scores from relative
# to absolute position. I don't know whether I might have got the time-offsets backwards or
# not, but let this code define which way round it is supposed to be.
if torch.jit.is_tracing():
(num_heads, batch_size, time1, n) = pos_scores.shape
rows = torch.arange(start=time1 - 1, end=-1, step=-1)
cols = torch.arange(seq_len)
rows = rows.repeat(batch_size * num_heads).unsqueeze(-1)
indexes = rows + cols
pos_scores = pos_scores.reshape(-1, n)
pos_scores = torch.gather(pos_scores, dim=1, index=indexes)
pos_scores = pos_scores.reshape(num_heads, batch_size, time1, seq_len)
else:
pos_scores = pos_scores.as_strided(
(num_heads, batch_size, seq_len, seq_len),
(
pos_scores.stride(0),
pos_scores.stride(1),
pos_scores.stride(2) - pos_scores.stride(3),
pos_scores.stride(3),
),
storage_offset=pos_scores.stride(3) * (seq_len - 1),
)
attn_scores = attn_scores + pos_scores
if torch.jit.is_scripting() or torch.jit.is_tracing():
pass
elif self.training and random.random() < 0.1:
# This is a harder way of limiting the attention scores to not be
# too large. It incurs a penalty if any of them has an absolute
# value greater than 50.0. this should be outside the normal range
# of the attention scores. We use this mechanism instead of, say,
# something added to the loss function involving the entropy,
# because once the entropy gets very small gradients through the
# softmax can become very small, and we'd get zero derivatives. The
# choices of 1.0e-04 as the scale on the penalty makes this
# mechanism vulnerable to the absolute scale of the loss function,
# but we view this as a failsafe to avoid "implausible" parameter
# values rather than a regularization method that should be active
# under normal circumstances.
attn_scores = penalize_abs_values_gt(
attn_scores, limit=25.0, penalty=1.0e-04, name=self.name
)
assert attn_scores.shape == (num_heads, batch_size, seq_len, seq_len)
if attn_mask is not None:
assert attn_mask.dtype == torch.bool
# use -1000 to avoid nan's where attn_mask and key_padding_mask make
# all scores zero. It's important that this be large enough that exp(-1000)
# is exactly zero, for reasons related to const_attention_rate, it
# compares the final weights with zero.
attn_scores = attn_scores.masked_fill(attn_mask, -1000)
if key_padding_mask is not None:
assert key_padding_mask.shape == (
batch_size,
seq_len,
), key_padding_mask.shape
attn_scores = attn_scores.masked_fill(
key_padding_mask.unsqueeze(1),
-1000,
)
# We use our own version of softmax, defined in scaling.py, which should
# save a little of the memory used in backprop by, if we are in
# automatic mixed precision mode (amp / autocast), by only storing the
# half-precision output for backprop purposes.
attn_weights = softmax(attn_scores, dim=-1)
if torch.jit.is_scripting() or torch.jit.is_tracing():
pass
elif random.random() < 0.001 and not self.training:
self._print_attn_entropy(attn_weights)
attn_weights = nn.functional.dropout(
attn_weights, p=self.dropout, training=self.training
)
return attn_weights
def streaming_forward(
self,
x: Tensor,
pos_emb: Tensor,
cached_key: Tensor,
left_context_len: int,
key_padding_mask: Tensor,
) -> Tuple[Tensor, Tensor]:
r"""
Args:
x: input of shape (seq_len, batch_size, embed_dim)
pos_emb: Positional embedding tensor, of shape (1, left_context_len+2*seq_len-1, pos_dim)
cached_key: cached attention key tensor of left context,
of shape (left_context_len, batch_size, key_dim)
left_context_len: number of left context frames.
key_padding_mask: a bool tensor of shape (batch_size, seq_len). Positions that
are True in this mask will be ignored as sources in the attention weighting.
Returns:
- attention weights, of shape (hum_heads, batch_size, seq_len, seq_len2),
interpreted as (hum_heads, batch_size, tgt_seq_len, src_seq_len).
- updated cached attention key tensor of left context.
"""
x = self.in_proj(x)
query_head_dim = self.query_head_dim
pos_head_dim = self.pos_head_dim
num_heads = self.num_heads
seq_len, batch_size, _ = x.shape
query_dim = query_head_dim * num_heads
# self-attention
q = x[..., 0:query_dim]
k = x[..., query_dim : 2 * query_dim]
# p is the position-encoding query
p = x[..., 2 * query_dim :]
assert p.shape[-1] == num_heads * pos_head_dim
# Pad cached left contexts
assert cached_key.shape[0] == left_context_len, (
cached_key.shape[0],
left_context_len,
)
k = torch.cat([cached_key, k], dim=0)
# Update cached left contexts
cached_key = k[-left_context_len:, ...]
# The length of key
k_len = k.shape[0]
q = q.reshape(seq_len, batch_size, num_heads, query_head_dim)
p = p.reshape(seq_len, batch_size, num_heads, pos_head_dim)
k = k.reshape(k_len, batch_size, num_heads, query_head_dim)
# time1 refers to target, time2 refers to source.
q = q.permute(2, 1, 0, 3) # (head, batch, time1, query_head_dim)
p = p.permute(2, 1, 0, 3) # (head, batch, time1, pos_head_dim)
k = k.permute(2, 1, 3, 0) # (head, batch, d_k, time2)
attn_scores = torch.matmul(q, k)
pos_emb = self.linear_pos(pos_emb)
seq_len2 = 2 * seq_len - 1 + left_context_len
pos_emb = pos_emb.reshape(-1, seq_len2, num_heads, pos_head_dim).permute(
2, 0, 3, 1
)
# pos shape now: (head, {1 or batch_size}, pos_dim, seq_len2)
# (head, batch, time1, pos_dim) x (head, 1, pos_dim, seq_len2) -> (head, batch, time1, seq_len2)
# [where seq_len2 represents relative position.]
pos_scores = torch.matmul(p, pos_emb)
if torch.jit.is_tracing():
(num_heads, batch_size, time1, n) = pos_scores.shape
rows = torch.arange(start=time1 - 1, end=-1, step=-1)
cols = torch.arange(k_len)
rows = rows.repeat(batch_size * num_heads).unsqueeze(-1)
indexes = rows + cols
pos_scores = pos_scores.reshape(-1, n)
pos_scores = torch.gather(pos_scores, dim=1, index=indexes)
pos_scores = pos_scores.reshape(num_heads, batch_size, time1, k_len)
# the following .as_strided() expression converts the last axis of pos_scores from relative
# to absolute position. I don't know whether I might have got the time-offsets backwards or
# not, but let this code define which way round it is supposed to be.
else:
pos_scores = pos_scores.as_strided(
(num_heads, batch_size, seq_len, k_len),
(
pos_scores.stride(0),
pos_scores.stride(1),
pos_scores.stride(2) - pos_scores.stride(3),
pos_scores.stride(3),
),
storage_offset=pos_scores.stride(3) * (seq_len - 1),
)
attn_scores = attn_scores + pos_scores
assert attn_scores.shape == (
num_heads,
batch_size,
seq_len,
k_len,
), attn_scores.shape
if key_padding_mask is not None:
assert key_padding_mask.shape == (batch_size, k_len), key_padding_mask.shape
attn_scores = attn_scores.masked_fill(
key_padding_mask.unsqueeze(1),
-1000,
)
attn_weights = attn_scores.softmax(dim=-1)
return attn_weights, cached_key
def _print_attn_entropy(self, attn_weights: Tensor):
# attn_weights: (num_heads, batch_size, seq_len, seq_len)
(num_heads, batch_size, seq_len, seq_len) = attn_weights.shape
with torch.no_grad():
with torch.cuda.amp.autocast(enabled=False):
attn_weights = attn_weights.to(torch.float32)
attn_weights_entropy = (
-((attn_weights + 1.0e-20).log() * attn_weights)
.sum(dim=-1)
.mean(dim=(1, 2))
)
logging.info(
f"name={self.name}, attn_weights_entropy = {attn_weights_entropy}"
)
class SelfAttention(nn.Module):
"""
The simplest possible attention module. This one works with already-computed attention
weights, e.g. as computed by RelPositionMultiheadAttentionWeights.
Args:
embed_dim: the input and output embedding dimension
num_heads: the number of attention heads
value_head_dim: the value dimension per head
"""
def __init__(
self,
embed_dim: int,
num_heads: int,
value_head_dim: int,
) -> None:
super().__init__()
self.in_proj = nn.Linear(embed_dim, num_heads * value_head_dim, bias=True)
self.out_proj = ScaledLinear(
num_heads * value_head_dim, embed_dim, bias=True, initial_scale=0.05
)
self.whiten = Whiten(
num_groups=1,
whitening_limit=_whitening_schedule(7.5, ratio=3.0),
prob=(0.025, 0.25),
grad_scale=0.01,
)
def forward(
self,
x: Tensor,
attn_weights: Tensor,
) -> Tensor:
"""
Args:
x: input tensor, of shape (seq_len, batch_size, embed_dim)
attn_weights: a tensor of shape (num_heads, batch_size, seq_len, seq_len),
with seq_len being interpreted as (tgt_seq_len, src_seq_len). Expect
attn_weights.sum(dim=-1) == 1.
Returns:
a tensor with the same shape as x.
"""
(seq_len, batch_size, embed_dim) = x.shape
num_heads = attn_weights.shape[0]
assert attn_weights.shape == (num_heads, batch_size, seq_len, seq_len)
x = self.in_proj(x) # (seq_len, batch_size, num_heads * value_head_dim)
x = x.reshape(seq_len, batch_size, num_heads, -1).permute(2, 1, 0, 3)
# now x: (num_heads, batch_size, seq_len, value_head_dim)
value_head_dim = x.shape[-1]
# todo: see whether there is benefit in overriding matmul
x = torch.matmul(attn_weights, x)
# v: (num_heads, batch_size, seq_len, value_head_dim)
x = (
x.permute(2, 1, 0, 3)
.contiguous()
.view(seq_len, batch_size, num_heads * value_head_dim)
)
# returned value is of shape (seq_len, batch_size, embed_dim), like the input.
x = self.out_proj(x)
x = self.whiten(x)
return x
def streaming_forward(
self,
x: Tensor,
attn_weights: Tensor,
cached_val: Tensor,
left_context_len: int,
) -> Tuple[Tensor, Tensor]:
"""
Args:
x: input tensor, of shape (seq_len, batch_size, embed_dim)
attn_weights: a tensor of shape (num_heads, batch_size, seq_len, seq_len),
with seq_len being interpreted as (tgt_seq_len, src_seq_len). Expect
attn_weights.sum(dim=-1) == 1.
cached_val: cached attention value tensor of left context,
of shape (left_context_len, batch_size, value_dim)
left_context_len: number of left context frames.
Returns:
- attention weighted output, a tensor with the same shape as x.
- updated cached attention value tensor of left context.
"""
(seq_len, batch_size, embed_dim) = x.shape
num_heads = attn_weights.shape[0]
seq_len2 = seq_len + left_context_len
assert attn_weights.shape == (num_heads, batch_size, seq_len, seq_len2)
x = self.in_proj(x) # (seq_len, batch_size, num_heads * value_head_dim)
# Pad cached left contexts
assert cached_val.shape[0] == left_context_len, (
cached_val.shape[0],
left_context_len,
)
x = torch.cat([cached_val, x], dim=0)
# Update cached left contexts
cached_val = x[-left_context_len:, ...]
x = x.reshape(seq_len2, batch_size, num_heads, -1).permute(2, 1, 0, 3)
# now x: (num_heads, batch_size, seq_len, value_head_dim)
value_head_dim = x.shape[-1]
# todo: see whether there is benefit in overriding matmul
x = torch.matmul(attn_weights, x)
# v: (num_heads, batch_size, seq_len, value_head_dim)
x = (
x.permute(2, 1, 0, 3)
.contiguous()
.view(seq_len, batch_size, num_heads * value_head_dim)
)
# returned value is of shape (seq_len, batch_size, embed_dim), like the input.
x = self.out_proj(x)
return x, cached_val
class FeedforwardModule(nn.Module):
"""Feedforward module in Zipformer2 model."""
def __init__(self, embed_dim: int, feedforward_dim: int, dropout: FloatLike):
super(FeedforwardModule, self).__init__()
self.in_proj = nn.Linear(embed_dim, feedforward_dim)
self.hidden_balancer = Balancer(
feedforward_dim,
channel_dim=-1,
min_positive=0.3,
max_positive=1.0,
min_abs=0.75,
max_abs=5.0,
)
# shared_dim=0 means we share the dropout mask along the time axis
self.out_proj = ActivationDropoutAndLinear(
feedforward_dim,
embed_dim,
activation="SwooshL",
dropout_p=dropout,
dropout_shared_dim=0,
bias=True,
initial_scale=0.1,
)
self.out_whiten = Whiten(
num_groups=1,
whitening_limit=_whitening_schedule(7.5),
prob=(0.025, 0.25),
grad_scale=0.01,
)
def forward(self, x: Tensor):
x = self.in_proj(x)
x = self.hidden_balancer(x)
# out_proj contains SwooshL activation, then dropout, then linear.
x = self.out_proj(x)
x = self.out_whiten(x)
return x
class NonlinAttention(nn.Module):
"""This is like the ConvolutionModule, but refactored so that we use multiplication by attention weights (borrowed
from the attention module) in place of actual convolution. We also took out the second nonlinearity, the
one after the attention mechanism.
Args:
channels (int): The number of channels of conv layers.
"""
def __init__(
self,
channels: int,
hidden_channels: int,
) -> None:
super().__init__()
self.hidden_channels = hidden_channels
self.in_proj = nn.Linear(channels, hidden_channels * 3, bias=True)
# balancer that goes before the sigmoid. Have quite a large min_abs value, at 2.0,
# because we noticed that well-trained instances of this module have abs-value before the sigmoid
# starting from about 3, and poorly-trained instances of the module have smaller abs values
# before the sigmoid.
self.balancer = Balancer(
hidden_channels,
channel_dim=-1,
min_positive=ScheduledFloat((0.0, 0.25), (20000.0, 0.05)),
max_positive=ScheduledFloat((0.0, 0.75), (20000.0, 0.95)),
min_abs=0.5,
max_abs=5.0,
)
self.tanh = nn.Tanh()
self.identity1 = Identity() # for diagnostics.
self.identity2 = Identity() # for diagnostics.
self.identity3 = Identity() # for diagnostics.
self.out_proj = ScaledLinear(
hidden_channels, channels, bias=True, initial_scale=0.05
)
self.whiten1 = Whiten(
num_groups=1,
whitening_limit=_whitening_schedule(5.0),
prob=(0.025, 0.25),
grad_scale=0.01,
)
self.whiten2 = Whiten(
num_groups=1,
whitening_limit=_whitening_schedule(5.0, ratio=3.0),
prob=(0.025, 0.25),
grad_scale=0.01,
)
def forward(
self,
x: Tensor,
attn_weights: Tensor,
) -> Tensor:
""".
Args:
x: a Tensor of shape (seq_len, batch_size, num_channels)
attn_weights: a Tensor of shape (num_heads, batch_size, seq_len, seq_len)
Returns:
a Tensor with the same shape as x
"""
x = self.in_proj(x)
(seq_len, batch_size, _) = x.shape
hidden_channels = self.hidden_channels
s, x, y = x.chunk(3, dim=2)
# s will go through tanh.
s = self.balancer(s)
s = self.tanh(s)
s = s.unsqueeze(-1).reshape(seq_len, batch_size, hidden_channels)
x = self.whiten1(x)
x = x * s
x = self.identity1(x) # diagnostics only, it's the identity.
(seq_len, batch_size, embed_dim) = x.shape
num_heads = attn_weights.shape[0]
assert attn_weights.shape == (num_heads, batch_size, seq_len, seq_len)
x = x.reshape(seq_len, batch_size, num_heads, -1).permute(2, 1, 0, 3)
# now x: (num_heads, batch_size, seq_len, head_dim)
x = torch.matmul(attn_weights, x)
# now x: (num_heads, batch_size, seq_len, head_dim)
x = x.permute(2, 1, 0, 3).reshape(seq_len, batch_size, -1)
y = self.identity2(y)
x = x * y
x = self.identity3(x)
x = self.out_proj(x)
x = self.whiten2(x)
return x
def streaming_forward(
self,
x: Tensor,
attn_weights: Tensor,
cached_x: Tensor,
left_context_len: int,
) -> Tuple[Tensor, Tensor]:
""".
Args:
x: a Tensor of shape (seq_len, batch_size, num_channels)
attn_weights: a Tensor of shape (num_heads, batch_size, seq_len, seq_len)
cached_x: left context, a Tensor of shape
(num_heads, batch_size, left_context_len, head_dim)
left_context_len: number of left context frames.
Returns:
- a Tensor with the same shape as x
- updated left context with same shape as cached_x
"""
x = self.in_proj(x)
(seq_len, batch_size, _) = x.shape
hidden_channels = self.hidden_channels
s, x, y = x.chunk(3, dim=2)
# s will go through tanh.
s = self.tanh(s)
s = s.unsqueeze(-1).reshape(seq_len, batch_size, hidden_channels)
x = x * s
(seq_len, batch_size, embed_dim) = x.shape
num_heads = attn_weights.shape[0]
assert attn_weights.shape == (
num_heads,
batch_size,
seq_len,
left_context_len + seq_len,
)
x = x.reshape(seq_len, batch_size, num_heads, -1).permute(2, 1, 0, 3)
# now x: (num_heads, batch_size, seq_len, head_dim)
# Pad cached tensor
assert cached_x.shape[2] == left_context_len, (
cached_x.shape[2],
left_context_len,
)
x_pad = torch.cat([cached_x, x], dim=2)
# Update cached tensor
cached_x = x_pad[:, :, -left_context_len:, :]
x = torch.matmul(attn_weights, x_pad)
# now x: (num_heads, batch_size, seq_len, head_dim)
x = x.permute(2, 1, 0, 3).reshape(seq_len, batch_size, -1)
x = x * y
x = self.out_proj(x)
return x, cached_x
class ConvolutionModule(nn.Module):
"""ConvolutionModule in Zipformer2 model.
Modified from https://github.com/espnet/espnet/blob/master/espnet/nets/pytorch_backend/zipformer/convolution.py
Args:
channels (int): The number of channels of conv layers.
kernel_size (int): Kernerl size of conv layers.
bias (bool): Whether to use bias in conv layers (default=True).
"""
def __init__(
self,
channels: int,
kernel_size: int,
causal: bool,
) -> None:
"""Construct a ConvolutionModule object."""
super(ConvolutionModule, self).__init__()
# kernerl_size should be a odd number for 'SAME' padding
assert (kernel_size - 1) % 2 == 0
bottleneck_dim = channels
self.causal = causal
self.in_proj = nn.Linear(
channels,
2 * bottleneck_dim,
)
# the gradients on in_proj are a little noisy, likely to do with the
# sigmoid in glu.
# after in_proj we put x through a gated linear unit (nn.functional.glu).
# For most layers the normal rms value of channels of x seems to be in the range 1 to 4,
# but sometimes, for some reason, for layer 0 the rms ends up being very large,
# between 50 and 100 for different channels. This will cause very peaky and
# sparse derivatives for the sigmoid gating function, which will tend to make
# the loss function not learn effectively. (for most layers the average absolute values
# are in the range 0.5..9.0, and the average p(x>0), i.e. positive proportion,
# at the output of pointwise_conv1.output is around 0.35 to 0.45 for different
# layers, which likely breaks down as 0.5 for the "linear" half and
# 0.2 to 0.3 for the part that goes into the sigmoid. The idea is that if we
# constrain the rms values to a reasonable range via a constraint of max_abs=10.0,
# it will be in a better position to start learning something, i.e. to latch onto
# the correct range.
self.balancer1 = Balancer(
bottleneck_dim,
channel_dim=-1,
min_positive=ScheduledFloat((0.0, 0.05), (8000.0, 0.025)),
max_positive=1.0,
min_abs=1.5,
max_abs=ScheduledFloat((0.0, 5.0), (8000.0, 10.0), default=1.0),
)
self.activation1 = Identity() # for diagnostics
self.sigmoid = nn.Sigmoid()
self.activation2 = Identity() # for diagnostics
assert kernel_size % 2 == 1
self.depthwise_conv = (
ChunkCausalDepthwiseConv1d(channels=bottleneck_dim, kernel_size=kernel_size)
if causal
else nn.Conv1d(
in_channels=bottleneck_dim,
out_channels=bottleneck_dim,
groups=bottleneck_dim,
kernel_size=kernel_size,
padding=kernel_size // 2,
)
)
self.balancer2 = Balancer(
bottleneck_dim,
channel_dim=1,
min_positive=ScheduledFloat((0.0, 0.1), (8000.0, 0.05)),
max_positive=1.0,
min_abs=ScheduledFloat((0.0, 0.2), (20000.0, 0.5)),
max_abs=10.0,
)
self.whiten = Whiten(
num_groups=1,
whitening_limit=_whitening_schedule(7.5),
prob=(0.025, 0.25),
grad_scale=0.01,
)
self.out_proj = ActivationDropoutAndLinear(
bottleneck_dim,
channels,
activation="SwooshR",
dropout_p=0.0,
initial_scale=0.05,
)
def forward(
self,
x: Tensor,
src_key_padding_mask: Optional[Tensor] = None,
chunk_size: int = -1,
) -> Tensor:
"""Compute convolution module.
Args:
x: Input tensor (#time, batch, channels).
src_key_padding_mask: the mask for the src keys per batch (optional):
(batch, #time), contains True in masked positions.
Returns:
Tensor: Output tensor (#time, batch, channels).
"""
x = self.in_proj(x) # (time, batch, 2*channels)
x, s = x.chunk(2, dim=2)
s = self.balancer1(s)
s = self.sigmoid(s)
x = self.activation1(x) # identity.
x = x * s
x = self.activation2(x) # identity
# (time, batch, channels)
# exchange the temporal dimension and the feature dimension
x = x.permute(1, 2, 0) # (#batch, channels, time).
if src_key_padding_mask is not None:
x = x.masked_fill(src_key_padding_mask.unsqueeze(1).expand_as(x), 0.0)
if (
not torch.jit.is_scripting()
and not torch.jit.is_tracing()
and chunk_size >= 0
):
# Not support exporting a model for simulated streaming decoding
assert (
self.causal
), "Must initialize model with causal=True if you use chunk_size"
x = self.depthwise_conv(x, chunk_size=chunk_size)
else:
x = self.depthwise_conv(x)
x = self.balancer2(x)
x = x.permute(2, 0, 1) # (time, batch, channels)
x = self.whiten(x) # (time, batch, channels)
x = self.out_proj(x) # (time, batch, channels)
return x
def streaming_forward(
self,
x: Tensor,
cache: Tensor,
src_key_padding_mask: Tensor,
) -> Tuple[Tensor, Tensor]:
"""Compute convolution module in streaming forward mode.
Args:
x: Input tensor (#time, batch, channels).
cache: cached left context for depthwise_conv of shape
(#batch, channels, left_pad)
src_key_padding_mask: the mask for the src keys per batch (optional):
(batch, #time), contains True in masked positions.
Returns:
- Output tensor (#time, batch, channels).
- Updated cache (#batch, channels, left_pad)
"""
x = self.in_proj(x) # (time, batch, 2*channels)
x, s = x.chunk(2, dim=2)
s = self.sigmoid(s)
x = x * s
# (time, batch, channels)
# exchange the temporal dimension and the feature dimension
x = x.permute(1, 2, 0) # (#batch, channels, time).
if src_key_padding_mask is not None:
x = x.masked_fill(src_key_padding_mask.unsqueeze(1).expand_as(x), 0.0)
x, cache = self.depthwise_conv.streaming_forward(x, cache=cache)
x = x.permute(2, 0, 1) # (time, batch, channels)
x = self.out_proj(x) # (time, batch, channels)
return x, cache
class ScalarMultiply(nn.Module):
def __init__(self, scale: float):
super().__init__()
self.scale = scale
def forward(self, x):
return x * self.scale
def _test_zipformer_main(causal: bool = False):
batch_size = 5
seq_len = 20
# Just make sure the forward pass runs.
c = Zipformer2(
encoder_dim=(64, 96),
encoder_unmasked_dim=(48, 64),
num_heads=(4, 4),
causal=causal,
chunk_size=(4,) if causal else (-1,),
left_context_frames=(64,),
)
batch_size = 5
seq_len = 20
# Just make sure the forward pass runs.
f = c(
torch.randn(seq_len, batch_size, 64),
torch.full((batch_size,), seq_len, dtype=torch.int64),
)
f[0].sum().backward()
c.eval()
f = c(
torch.randn(seq_len, batch_size, 64),
torch.full((batch_size,), seq_len, dtype=torch.int64),
)
f # to remove flake8 warnings
if __name__ == "__main__":
logging.getLogger().setLevel(logging.INFO)
torch.set_num_threads(1)
torch.set_num_interop_threads(1)
_test_zipformer_main(False)
_test_zipformer_main(True)
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