Add more documentation about the amplification value.

diff --git a/afs.cmd b/afs.cmd
index 8d8ee12347b89ee69fa1647b6383fa61a7eb181d..5c9f1ecb5c78cd01a8dbcf86b7adc5cd4e6449d5 100644 (file)
--- a/afs.cmd
+++ b/afs.cmd
@@ -202,7 +202,13 @@ H:         this audio file.
 H:
 H: -i  Set the image id. Same as -y, but sets the image.
 H:
-H: -a  Set the amplification value (0-255).
+H: -a  Set the amplification value (0-255). This determines a scaling
+H:     factor by which the amplitude should be multiplied in order to
+H:     normalize the volume of the audio file.  A value of zero means
+H:     no amplification, 64 means the amplitude should be multiplied
+H:     by a factor of two, 128 by three and so on.
+H:
+H:     This value is used by the compress filter.
 H:
 H: -v  Verbose mode. Explain what is being done.
 H: