diff --git a/egs/librispeech/ASR/pruned_transducer_stateless7/scaling.py b/egs/librispeech/ASR/pruned_transducer_stateless7/scaling.py
index ed3784a78..39b08e169 100644
--- a/egs/librispeech/ASR/pruned_transducer_stateless7/scaling.py
+++ b/egs/librispeech/ASR/pruned_transducer_stateless7/scaling.py
@@ -928,7 +928,6 @@ class DoubleSwishFunction(torch.autograd.Function):
         d = (d * ((ceil - floor) / 255.0) + floor)
         return (y_grad * d)
 
-
 class DoubleSwish(torch.nn.Module):
     def forward(self, x: Tensor) -> Tensor:
         """Return double-swish activation function which is an approximation to Swish(Swish(x)),
@@ -939,6 +938,68 @@ class DoubleSwish(torch.nn.Module):
         return DoubleSwishFunction.apply(x)
 
 
+class TanSwishFunction(torch.autograd.Function):
+    """
+      double_swish(x) = tan(x) * torch.sigmoid(x-1)
+
+
+      entering: d/dx(tanh(x) * sigmoid(x-1))
+      into wolfram alpha, I see that the range of this function is
+        -0.0498087 <= y <= 0.417894
+      let's make it (as we don't know how this was rounded):
+        -0.0498088 <= y <= 0.417895
+    """
+
+    @staticmethod
+    def forward(ctx, x: Tensor) -> Tensor:
+        requires_grad = x.requires_grad
+        if not requires_grad:
+            return torch.tanh(x) * torch.sigmoid(x - 1.0)
+
+        x_dtype = x.dtype
+        if x.dtype == torch.float16:
+            x = x.to(torch.float32)
+
+        with torch.cuda.amp.autocast(enabled=False):
+            with torch.enable_grad():
+                x = x.detach()
+                x.requires_grad = True
+                y = torch.tanh(x) * torch.sigmoid(x - 1.0)
+                y.backward(gradient=torch.ones_like(y))
+                grad = x.grad
+                floor = -0.0498088
+                ceil = 0.417895
+                d_scaled = ((grad - floor) * (255.0 / (ceil - floor)) + torch.rand_like(grad))
+                if __name__ == "__main__":
+                    # for self-testing only.
+                    assert d_scaled.min() >= 0.0
+                    assert d_scaled.max() < 256.0
+
+                d_int = d_scaled.to(torch.uint8)
+                ctx.save_for_backward(d_int)
+                if x.dtype == torch.float16 or torch.is_autocast_enabled():
+                    y = y.to(torch.float16)
+                return y
+
+    @staticmethod
+    def backward(ctx, y_grad: Tensor) -> Tensor:
+        d, = ctx.saved_tensors
+        # the same constants as used in forward pass.
+        floor = -0.0498088
+        ceil = 0.417895
+        d = (d * ((ceil - floor) / 255.0) + floor)
+        return (y_grad * d)
+
+
+class TanSwish(torch.nn.Module):
+    def forward(self, x: Tensor) -> Tensor:
+        """Return tan-swish activation function which is tanh(x) sigmoid(x-1)n
+        """
+        if torch.jit.is_scripting():
+            return x.tanh() * torch.sigmoid(x - 1.0)
+        return TanSwishFunction.apply(x)
+
+
 class ScheduledFloat(torch.nn.Module):
     """
     This object is a torch.nn.Module only because we want it to show up in [top_level module].modules();
@@ -1147,6 +1208,20 @@ def _test_double_swish_deriv():
     x.requires_grad = True
     y = m(x)
 
+def _test_tan_swish_deriv():
+    x = torch.randn(10, 12, dtype=torch.double) * 3.0
+    x.requires_grad = True
+    m = TanSwish()
+
+    tol = ((1.2-(-0.043637))/255.0)
+    torch.autograd.gradcheck(m, x, atol=tol)
+
+
+    # for self-test.
+    x = torch.randn(1000, 1000, dtype=torch.double) * 3.0
+    x.requires_grad = True
+    y = m(x)
+
 
 
 def _test_softmax():
@@ -1173,3 +1248,4 @@ if __name__ == "__main__":
     _test_activation_balancer_magnitude()
     _test_basic_norm()
     _test_double_swish_deriv()
+    _test_tan_swish_deriv()
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless7/zipformer.py b/egs/librispeech/ASR/pruned_transducer_stateless7/zipformer.py
index 7332a9eda..fa2bd448d 100644
--- a/egs/librispeech/ASR/pruned_transducer_stateless7/zipformer.py
+++ b/egs/librispeech/ASR/pruned_transducer_stateless7/zipformer.py
@@ -29,6 +29,7 @@ from scaling import (
     BasicNorm,
     MaxEig,
     DoubleSwish,
+    TanSwish,
     ScaledConv1d,
     ScaledLinear,  # not as in other dirs.. just scales down initial parameter values.
     Whiten,
@@ -1317,7 +1318,7 @@ class AttentionSqueeze(nn.Module):
             max_factor=0.02,
             min_prob=0.1,
         )
-        self.bottleneck_activation = nn.Tanh()   # in bottleneck
+        self.bottleneck_activation = TanSwish()   # in bottleneck
         self.activation = Identity() # for diagnostics
 
         # the next two balancers are only to stop parameter-magnitude 'drift': we have