diff --git a/paddlespeech/t2s/modules/diffnet.py b/paddlespeech/t2s/modules/diffnet.py
index 607fbd19d..deae4847f 100644
--- a/paddlespeech/t2s/modules/diffnet.py
+++ b/paddlespeech/t2s/modules/diffnet.py
@@ -120,6 +120,7 @@ class SinusoidalPosEmb(nn.Layer):
         self.dim = dim
 
     def forward(self, x: paddle.Tensor):
+        # check if x is 0-dim tensor, if so, add a dimension
         if x.ndim == 0:
             x = paddle.cast(x.unsqueeze(0), 'float32')
         else:
diff --git a/paddlespeech/t2s/modules/nets_utils.py b/paddlespeech/t2s/modules/nets_utils.py
index e32be0706..a3c6947b8 100644
--- a/paddlespeech/t2s/modules/nets_utils.py
+++ b/paddlespeech/t2s/modules/nets_utils.py
@@ -181,6 +181,7 @@ def make_pad_mask(lengths, xs=None, length_dim=-1):
     if length_dim == 0:
         raise ValueError("length_dim cannot be 0: {}".format(length_dim))
 
+    # check if lengths is 0-dim tensor, if so, add a dimension
     if lengths.ndim == 0:
         bs = paddle.shape(lengths.unsqueeze(0))
     else: