diff --git a/egs/librispeech/ASR/pruned_transducer_stateless7/conformer.py b/egs/librispeech/ASR/pruned_transducer_stateless7/conformer.py
index 2edfe376e..ffaa6660f 100644
--- a/egs/librispeech/ASR/pruned_transducer_stateless7/conformer.py
+++ b/egs/librispeech/ASR/pruned_transducer_stateless7/conformer.py
@@ -41,7 +41,7 @@ class Conformer(EncoderInterface):
     Args:
         num_features (int): Number of input features
         subsampling_factor (int): subsampling factor of encoder (the convolution layers before transformers)
-        d_model (int): attention dimension, also the output dimension
+        d_model (int): (attention_dim1, attention_dim2, output_dim)
         nhead (int): number of head
         dim_feedforward (int): feedforward dimention
         num_encoder_layers (int): number of encoder layers
@@ -55,13 +55,13 @@ class Conformer(EncoderInterface):
         self,
         num_features: int,
         subsampling_factor: int = 4,
-        d_model: int = 256,
-        nhead: int = 4,
-        dim_feedforward: int = 2048,
-        num_encoder_layers: int = 12,
+        conformer_subsampling_factor: int = 4,
+        d_model: Tuple[int] = (256, 384, 512),
+        nhead: Tuple[int] = (8, 8),
+        feedforward_dim: Tuple[int] = (1536, 2048),
+        num_encoder_layers: Tuple[int] = (12, 12),
         dropout: float = 0.1,
-        layer_dropout: float = 0.25,
-        cnn_module_kernel: int = 31,
+        cnn_module_kernel: Tuple[int] = (31, 31),
     ) -> None:
         super(Conformer, self).__init__()
 
@@ -75,22 +75,42 @@ class Conformer(EncoderInterface):
         # That is, it does two things simultaneously:
         #   (1) subsampling: T -> T//subsampling_factor
         #   (2) embedding: num_features -> d_model
-        self.encoder_embed = Conv2dSubsampling(num_features, d_model)
+        self.encoder_embed = Conv2dSubsampling(num_features, d_model[0],
+                                               dropout=dropout)
 
-        self.encoder_pos = RelPositionalEncoding(d_model, dropout)
-
-        encoder_layer = ConformerEncoderLayer(
-            d_model,
-            nhead,
-            dim_feedforward,
+        encoder_layer1 = ConformerEncoderLayer(
+            d_model[0],
+            nhead[0],
+            feedforward_dim[0],
             dropout,
-            cnn_module_kernel,
+            cnn_module_kernel[0],
+
         )
-        self.encoder = ConformerEncoder(
-            encoder_layer,
-            num_encoder_layers,
-            layer_dropout=layer_dropout,
+        self.encoder1 = ConformerEncoder(
+            encoder_layer1,
+            num_encoder_layers[0],
+            dropout,
         )
+        encoder_layer2 = ConformerEncoderLayer(
+            d_model[1],
+            nhead[1],
+            feedforward_dim[1],
+            dropout,
+            cnn_module_kernel[1],
+        )
+        self.encoder2 = DownsampledConformerEncoder(
+            ConformerEncoder(
+                encoder_layer2,
+                num_encoder_layers[1],
+                dropout,
+            ),
+            input_dim=d_model[0],
+            output_dim=d_model[1],
+            downsample=conformer_subsampling_factor,
+        )
+
+        self.out_combiner = SimpleCombiner(d_model[0],
+                                           d_model[1])
 
 
     def forward(
@@ -110,7 +130,7 @@ class Conformer(EncoderInterface):
               of frames in `embeddings` before padding.
         """
         x = self.encoder_embed(x)
-        x, pos_emb = self.encoder_pos(x)
+
         x = x.permute(1, 0, 2)  # (N, T, C) -> (T, N, C)
 
         with warnings.catch_warnings():
@@ -120,9 +140,17 @@ class Conformer(EncoderInterface):
         assert x.size(0) == lengths.max().item()
         mask = make_pad_mask(lengths)
 
-        x = self.encoder(
-            x, pos_emb, src_key_padding_mask=mask,
-        )  # (T, N, C)
+        # x1:
+        x1 = self.encoder1(
+            x, src_key_padding_mask=mask,
+        )  # (T, N, C) where C == d_model[0]
+
+        x2 = self.encoder2(
+            x1, src_key_padding_mask=mask,
+        )  # (T, N, C) where C == d_model[1]
+
+        x = self.out_combiner(x1, x2)
+
 
         x = x.permute(1, 0, 2)  # (T, N, C) ->(N, T, C)
 
@@ -137,7 +165,7 @@ class ConformerEncoderLayer(nn.Module):
     Args:
         d_model: the number of expected features in the input (required).
         nhead: the number of heads in the multiheadattention models (required).
-        dim_feedforward: the dimension of the feedforward network model (default=2048).
+        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.
 
@@ -151,7 +179,7 @@ class ConformerEncoderLayer(nn.Module):
         self,
         d_model: int,
         nhead: int,
-        dim_feedforward: int = 2048,
+        feedforward_dim: int = 2048,
         dropout: float = 0.1,
         cnn_module_kernel: int = 31,
     ) -> None:
@@ -164,22 +192,22 @@ class ConformerEncoderLayer(nn.Module):
         )
 
         self.feed_forward = nn.Sequential(
-            nn.Linear(d_model, dim_feedforward),
-            ActivationBalancer(dim_feedforward,
+            nn.Linear(d_model, feedforward_dim),
+            ActivationBalancer(feedforward_dim,
                                channel_dim=-1, max_abs=10.0),
             DoubleSwish(),
             nn.Dropout(dropout),
-            ScaledLinear(dim_feedforward, d_model,
+            ScaledLinear(feedforward_dim, d_model,
                          initial_scale=0.01),
         )
 
         self.feed_forward_macaron = nn.Sequential(
-            nn.Linear(d_model, dim_feedforward),
-            ActivationBalancer(dim_feedforward,
+            nn.Linear(d_model, feedforward_dim),
+            ActivationBalancer(feedforward_dim,
                                channel_dim=-1, max_abs=10.0),
             DoubleSwish(),
             nn.Dropout(dropout),
-            ScaledLinear(dim_feedforward, d_model,
+            ScaledLinear(feedforward_dim, d_model,
                          initial_scale=0.01),
         )
 
@@ -261,22 +289,23 @@ class ConformerEncoder(nn.Module):
         >>> encoder_layer = ConformerEncoderLayer(d_model=512, nhead=8)
         >>> conformer_encoder = ConformerEncoder(encoder_layer, num_layers=6)
         >>> src = torch.rand(10, 32, 512)
-        >>> pos_emb = torch.rand(32, 19, 512)
-        >>> out = conformer_encoder(src, pos_emb)
+        >>> out = conformer_encoder(src)
+
+
+    Returns: (combined_output, output),
+        where `combined_output` has gone through the RandomCombiner module and `output` is just the
+        original output, in case you need to bypass the RandomCombiner module.
     """
     def __init__(
         self,
         encoder_layer: nn.Module,
         num_layers: int,
-        layer_dropout: float = 0.25
+        dropout: float
     ) -> None:
         super().__init__()
-        assert 0 < layer_dropout < 0.5
-        # `count` tracks how many times the forward function has been called
-        # since we initialized the model (it is not written to disk or read when
-        # we resume training).  It is used for random seeding for layer dropping.
-        self.count = 0
-        self.layer_dropout = layer_dropout
+
+        self.encoder_pos = RelPositionalEncoding(encoder_layer.d_model,
+                                                 dropout)
 
         self.layers = nn.ModuleList(
             [copy.deepcopy(encoder_layer) for i in range(num_layers)]
@@ -287,19 +316,16 @@ class ConformerEncoder(nn.Module):
         num_channels = encoder_layer.norm_final.num_channels
 
 
-
     def forward(
         self,
         src: Tensor,
-        pos_emb: Tensor,
         mask: Optional[Tensor] = None,
         src_key_padding_mask: Optional[Tensor] = None,
-    ) -> Tensor:
+    ) -> Tuple[Tensor, Tensor]:
         r"""Pass the input through the encoder layers in turn.
 
         Args:
             src: the sequence to the encoder (required).
-            pos_emb: Positional embedding tensor (required).
             mask: the mask for the src sequence (optional).
             src_key_padding_mask: the mask for the src keys per batch (optional).
 
@@ -310,7 +336,9 @@ class ConformerEncoder(nn.Module):
             src_key_padding_mask: (N, S).
             S is the source sequence length, T is the target sequence length, N is the batch size, E is the feature number
 
+        Returns: (x, x_no_combine), both of shape (S, N, E)
         """
+        pos_emb = self.encoder_pos(src)
         output = src
 
         outputs = []
@@ -337,7 +365,6 @@ class ConformerEncoder(nn.Module):
             frame_mask = torch.logical_or(frame_mask,
                                           torch.rand_like(src[:,:1,:1]) < 0.1)
 
-
             feature_mask[..., feature_unmasked_dim:] *= frame_mask
 
 
@@ -364,11 +391,190 @@ class ConformerEncoder(nn.Module):
                 src_mask=mask,
                 src_key_padding_mask=src_key_padding_mask,
             )
+
             output = output * feature_mask
 
         return output
 
 
+class DownsampledConformerEncoder(nn.Module):
+    r"""
+    DownsampledConformerEncoder is a conformer encoder evaluated at a reduced frame rate,
+    after convolutional downsampling, and then upsampled again at the output
+    so that the output has the same shape as the input.
+    """
+    def __init__(self,
+                 encoder: nn.Module,
+                 input_dim: int,
+                 output_dim: int,
+                 downsample: int):
+        super(DownsampledConformerEncoder, self).__init__()
+        self.downsample_factor = downsample
+        self.downsample = AttentionDownsample(input_dim, output_dim, downsample)
+        self.encoder = encoder
+        self.upsample = SimpleUpsample(output_dim, downsample)
+
+
+    def forward(self,
+                src: Tensor,
+                mask: Optional[Tensor] = None,
+                src_key_padding_mask: Optional[Tensor] = None,
+    ) -> Tuple[Tensor, Tensor]:
+        r"""Downsample, go through encoder, upsample.
+
+        Args:
+            src: the sequence to the encoder (required).
+            mask: the mask for the src sequence (optional).  CAUTION: we need to downsample
+                  this, if we are to support it.  Won't work correctly yet.
+            src_key_padding_mask: the mask for the src keys per batch (optional).
+
+        Shape:
+            src: (S, N, E).
+            mask: (S, S).
+            src_key_padding_mask: (N, S).
+            S is the source sequence length, T is the target sequence length, N is the batch size, E is the feature number
+
+        Returns: output of shape (S, N, F) where F is the number of output features
+            (output_dim to constructor)
+        """
+        src_orig = src
+        src = self.downsample(src)
+        ds = self.downsample_factor
+        if mask is not None:
+            mask = mask[::ds,::ds]
+        if src_key_padding_mask is not None:
+            src_key_padding_mask = src_key_padding_mask[::ds]
+
+        src = self.encoder(
+            src, src_key_padding_mask=mask,
+        )
+        src = self.upsample(src)
+        # remove any extra frames that are not a multiple of downsample_factor
+        src = src[:src_orig.shape[0]]
+
+        return src
+
+
+class AttentionDownsample(torch.nn.Module):
+    """
+    Does downsampling with attention, by weighted sum, and a projection..
+    """
+    def __init__(self,
+                 in_channels: int,
+                 out_channels: int,
+                 downsample: int):
+        """
+        Require out_channels > in_channels.
+        """
+        super(AttentionDownsample, self).__init__()
+        self.query = nn.Parameter(torch.randn(in_channels) * (in_channels ** -0.5))
+
+        # fill in the extra dimensions with a projection of the input
+        if out_channels > in_channels:
+            self.extra_proj = nn.Linear(in_channels * downsample,
+                                        out_channels - in_channels,
+                                        bias=False)
+        else:
+            self.extra_proj = None
+        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, out_channels)
+        """
+        (seq_len, batch_size, in_channels) = src.shape
+        ds = self.downsample
+        d_seq_len = (seq_len + ds - 1) // ds
+        src_orig = src
+        # Pad to an exact multiple of self.downsample
+        if seq_len != d_seq_len * ds:
+            # 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)
+        scores = (src * self.query).sum(dim=-1, keepdim=True)
+        weights = scores.softmax(dim=1)
+
+        # ans1 is the first `in_channels` channels of the output
+        ans = (src * weights).sum(dim=1)
+        src = src.permute(0, 2, 1, 3).reshape(d_seq_len, batch_size, ds * in_channels)
+
+        if self.extra_proj is not None:
+            ans2 = self.extra_proj(src)
+            ans = torch.cat((ans, ans2), dim=2)
+        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.bias = nn.Parameter(torch.randn(upsample, num_channels) * 0.01)
+
+    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.bias.shape[0]
+        (seq_len, batch_size, num_channels) = src.shape
+        src = src.unsqueeze(1).expand(seq_len, upsample, batch_size, num_channels)
+        src = src + self.bias.unsqueeze(1)
+        src = src.reshape(seq_len * upsample, batch_size, num_channels)
+        return src
+
+class SimpleCombiner(torch.nn.Module):
+    """
+    A very simple way of combining 2 vectors of 2 different dims, via a
+    learned weighted combination in the shared part of the dim.
+
+    """
+    def __init__(self,
+                 dim1: int,
+                 dim2: int):
+        super(SimpleCombiner, self).__init__()
+        assert dim2 >= dim1
+        self.to_weight1 = nn.Parameter(torch.randn(dim1) * 0.01)
+        self.to_weight2 = nn.Parameter(torch.randn(dim2) * 0.01)
+
+
+    def forward(self,
+                src1: Tensor,
+                src2: Tensor) -> Tensor:
+        """
+        src1: (*, dim1)
+        src2: (*, dim2)
+
+        Returns: a tensor of shape (*, dim2)
+        """
+        assert src1.shape[:-1] == src2.shape[:-1]
+        dim1 = src1.shape[-1]
+        dim2 = src2.shape[-1]
+
+        weight1 = (src1 * self.to_weight1).sum(dim=-1, keepdim=True)
+        weight2 = (src2 * self.to_weight2).sum(dim=-1, keepdim=True)
+        weight = (weight1 + weight2).sigmoid()
+
+        src2_part1 = src2[...,:dim1]
+        part1 = src1 * weight + src2_part1 * (1.0 - weight)
+        part2 = src2[...,dim1:]
+        return torch.cat((part1, part2), dim=-1)
+
+
+
 class RelPositionalEncoding(torch.nn.Module):
     """Relative positional encoding module.
 
@@ -385,7 +591,7 @@ class RelPositionalEncoding(torch.nn.Module):
     def __init__(
         self, d_model: int, dropout_rate: float, max_len: int = 5000
     ) -> None:
-        """Construct an PositionalEncoding object."""
+        """Construct a PositionalEncoding object."""
         super(RelPositionalEncoding, self).__init__()
         self.d_model = d_model
         self.dropout = torch.nn.Dropout(dropout_rate)
@@ -397,7 +603,7 @@ class RelPositionalEncoding(torch.nn.Module):
         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(1) >= x.size(1) * 2 - 1:
+            if self.pe.size(1) >= x.size(0) * 2 - 1:
                 # Note: TorchScript doesn't implement operator== for torch.Device
                 if self.pe.dtype != x.dtype or str(self.pe.device) != str(
                     x.device
@@ -407,9 +613,9 @@ class RelPositionalEncoding(torch.nn.Module):
         # Suppose `i` means to the position of query vecotr and `j` means the
         # position of key vector. We use position relative positions when keys
         # are to the left (i>j) and negative relative positions otherwise (i<j).
-        pe_positive = torch.zeros(x.size(1), self.d_model)
-        pe_negative = torch.zeros(x.size(1), self.d_model)
-        position = torch.arange(0, x.size(1), dtype=torch.float32).unsqueeze(1)
+        pe_positive = torch.zeros(x.size(0), self.d_model)
+        pe_negative = torch.zeros(x.size(0), self.d_model)
+        position = torch.arange(0, x.size(0), dtype=torch.float32).unsqueeze(1)
         div_term = torch.exp(
             torch.arange(0, self.d_model, 2, dtype=torch.float32)
             * -(math.log(10000.0) / self.d_model)
@@ -431,7 +637,7 @@ class RelPositionalEncoding(torch.nn.Module):
         """Add positional encoding.
 
         Args:
-            x (torch.Tensor): Input tensor (batch, time, `*`).
+            x (torch.Tensor): Input tensor (time, batch, `*`).
 
         Returns:
             torch.Tensor: Encoded tensor (batch, time, `*`).
@@ -442,11 +648,11 @@ class RelPositionalEncoding(torch.nn.Module):
         pos_emb = self.pe[
             :,
             self.pe.size(1) // 2
-            - x.size(1)
+            - x.size(0)
             + 1 : self.pe.size(1) // 2  # noqa E203
-            + x.size(1),
+            + x.size(0),
         ]
-        return self.dropout(x), self.dropout(pos_emb)
+        return self.dropout(pos_emb)
 
 
 class RelPositionMultiheadAttention(nn.Module):
@@ -478,7 +684,7 @@ class RelPositionMultiheadAttention(nn.Module):
         self.head_dim = embed_dim // (num_heads * 2)
         assert (
             self.head_dim * num_heads == self.embed_dim // 2
-        ), "embed_dim must be divisible by num_heads"
+        ), "embed_dim//2 must be divisible by num_heads"
 
         self.in_proj = nn.Linear(embed_dim, 3 * embed_dim // 2, bias=True)
         self.in_balancer = ActivationBalancer(3 * embed_dim // 2,
@@ -965,6 +1171,7 @@ class Conv2dSubsampling(nn.Module):
         layer1_channels: int = 8,
         layer2_channels: int = 32,
         layer3_channels: int = 128,
+        dropout: float = 0.1,
     ) -> None:
         """
         Args:
@@ -1012,6 +1219,7 @@ class Conv2dSubsampling(nn.Module):
         )
         out_height = (((in_channels - 1) // 2 - 1) // 2)
         self.out = ScaledLinear(out_height * layer3_channels, out_channels)
+        self.dropout = nn.Dropout(dropout)
 
 
     def forward(self, x: torch.Tensor) -> torch.Tensor:
@@ -1031,6 +1239,7 @@ class Conv2dSubsampling(nn.Module):
         b, c, t, f = x.size()
         x = self.out(x.transpose(1, 2).contiguous().view(b, t, c * f))
         # Now x is of shape (N, ((T-1)//2 - 1))//2, odim)
+        x = self.dropout(x)
         return x
 
 class AttentionCombine(nn.Module):
@@ -1166,14 +1375,13 @@ def _test_random_combine():
 
 def _test_conformer_main():
     feature_dim = 50
-    c = Conformer(num_features=feature_dim, d_model=128, nhead=4)
     batch_size = 5
     seq_len = 20
     feature_dim = 50
     # Just make sure the forward pass runs.
 
     c = Conformer(
-        num_features=feature_dim, d_model=128, nhead=4
+        num_features=feature_dim, d_model=(64,96,128), nhead=(4,4)
     )
     batch_size = 5
     seq_len = 20
@@ -1191,8 +1399,6 @@ def _test_conformer_main():
     f  # to remove flake8 warnings
 
 
-
-
 if __name__ == "__main__":
     logging.getLogger().setLevel(logging.INFO)
     torch.set_num_threads(1)
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless7/train.py b/egs/librispeech/ASR/pruned_transducer_stateless7/train.py
index d3680e75e..fda28302f 100755
--- a/egs/librispeech/ASR/pruned_transducer_stateless7/train.py
+++ b/egs/librispeech/ASR/pruned_transducer_stateless7/train.py
@@ -91,30 +91,38 @@ LRSchedulerType = Union[
 def add_model_arguments(parser: argparse.ArgumentParser):
     parser.add_argument(
         "--num-encoder-layers",
-        type=int,
-        default=24,
-        help="Number of conformer encoder layers..",
+        type=str,
+        default="12,12",
+        help="Number of conformer encoder layers, comma separated.",
     )
 
     parser.add_argument(
-        "--dim-feedforward",
-        type=int,
-        default=1536,
-        help="Feedforward dimension of the conformer encoder layer.",
+        "--feedforward-dims",
+        type=str,
+        default="1536,1536",
+        help="Feedforward dimension of the conformer encoder layers, comma separated.",
     )
 
     parser.add_argument(
         "--nhead",
-        type=int,
-        default=8,
-        help="Number of attention heads in the conformer encoder layer.",
+        type=str,
+        default="8,8",
+        help="Number of attention heads in the conformer encoder layers.",
     )
 
     parser.add_argument(
-        "--encoder-dim",
+        "--encoder-dims",
+        type=str,
+        default="384,384",
+        help="Attention dimension in 2, blocks of conformer encoder layers, comma separated, "
+        "and the output dim of the encoder",
+    )
+
+    parser.add_argument(
+        "--conformer-subsampling-factor",
         type=int,
-        default=384,
-        help="Attention dimension in the conformer encoder layer.",
+        default=2,
+        help="Subsampling factor for 2nd stack of encoder layers.",
     )
 
     parser.add_argument(
@@ -401,13 +409,16 @@ def get_params() -> AttributeDict:
 
 def get_encoder_model(params: AttributeDict) -> nn.Module:
     # TODO: We can add an option to switch between Conformer and Transformer
+    def to_int_list(s: str):
+        return list(map(int, s.split(',')))
     encoder = Conformer(
         num_features=params.feature_dim,
         subsampling_factor=params.subsampling_factor,
-        d_model=params.encoder_dim,
-        nhead=params.nhead,
-        dim_feedforward=params.dim_feedforward,
-        num_encoder_layers=params.num_encoder_layers,
+        conformer_subsampling_factor=params.conformer_subsampling_factor,
+        d_model=to_int_list(params.encoder_dims),
+        nhead=to_int_list(params.nhead),
+        feedforward_dim=to_int_list(params.feedforward_dims),
+        num_encoder_layers=to_int_list(params.num_encoder_layers),
     )
     return encoder
 
@@ -424,7 +435,7 @@ def get_decoder_model(params: AttributeDict) -> nn.Module:
 
 def get_joiner_model(params: AttributeDict) -> nn.Module:
     joiner = Joiner(
-        encoder_dim=params.encoder_dim,
+        encoder_dim=int(params.encoder_dims.split(',')[-1]),
         decoder_dim=params.decoder_dim,
         joiner_dim=params.joiner_dim,
         vocab_size=params.vocab_size,
@@ -441,7 +452,7 @@ def get_transducer_model(params: AttributeDict) -> nn.Module:
         encoder=encoder,
         decoder=decoder,
         joiner=joiner,
-        encoder_dim=params.encoder_dim,
+        encoder_dim=int(params.encoder_dims.split(',')[-1]),
         decoder_dim=params.decoder_dim,
         joiner_dim=params.joiner_dim,
         vocab_size=params.vocab_size,