TDT fix

Signed-off-by: arushid <arushid@nvidia.com>

Author: arushidNV

nemo/collections/asr/parts/preprocessing/features.py

@@ -81,7 +81,9 @@ def normalize_batch(x, seq_len, normalize_type):
         x_std = x_std.masked_fill(x_std.isnan(), 0.0)  # edge case: only 1 frame in denominator
         # make sure x_std is not zero
         x_std += CONSTANT
-        return (x - x_mean.unsqueeze(2)) / x_std.unsqueeze(2), x_mean, x_std
+        normalized = (x - x_mean.unsqueeze(2)) / x_std.unsqueeze(2)
+        normalized.masked_fill_(~valid_mask.unsqueeze(1), 0.0)
+        return normalized, x_mean, x_std
     elif normalize_type == "all_features":
         x_mean = torch.zeros(seq_len.shape, dtype=x.dtype, device=x.device)
         x_std = torch.zeros(seq_len.shape, dtype=x.dtype, device=x.device)