diff --git a/README.md b/README.md
index 86ad9d3..8b3f861 100644
--- a/README.md
+++ b/README.md
@@ -45,6 +45,9 @@ However, this may sacrifice the accuracy.
 whispering --language en --model tiny -n 20 --allow-padding
 ```
 
+Without ``--allow-padding``, whispering just performs VAD for the period,
+and when it is predicted as "silence", it will not be passed to whisper.
+
 ## Example of web socket
 
 ⚠  **No security mechanism. Please make secure with your responsibility.**
diff --git a/whispering/cli.py b/whispering/cli.py
index 33e3e13..1af32e7 100644
--- a/whispering/cli.py
+++ b/whispering/cli.py
@@ -158,7 +158,7 @@ def get_opts() -> argparse.Namespace:
         "--num_block",
         "-n",
         type=int,
-        default=160,
+        default=20,
         help="Number of operation unit",
     )
     group_misc.add_argument(