[Asterisk-Users] gsm codec, very poor quality.

[Kevin P. Fleming]

Andrei (MPI) wrote:

> I am using wav format for prompts. I see no reason to use gsm or 
> anything else, if disk space is not a problem.
> The same as using ulaw if bandwidth is not a problem.

If your callers are coming in over PSTN connections, then you should 
store your prompts in ulaw (.ul) or alaw (.al) files. There is no value 
in storing them in any WAV-type format at all, since Asterisk will still 
have to translate them. Realistically, though, you should store all your 
prompts in every format your callers are likely to use: Asterisk will 
choose the "best" format to play back when it is needed.

sox does an excellent job of converting the Digium-supplied GSM files 
into ulaw files. Obviously the sound quality does not improve (without 
access to the original uncompressed material), but it saves a small 
amount of CPU time on the server doing the playback.