[Asterisk-Users] Asterisk and Wave files problem

[Elwin Andriol]

Christian wrote:

> Hi,
> I'm recording wave files but I cant get Asterisk to play them, only if 
> they are in 8000 Hz. What is the maximum sample rate Asterisk can 
> handle? I have been using 16-bit 44.1, 22050 and finally 8000 kHz.

To my knowledge, the only correct format for wav files to use in 
asterisk is 16-bit 8 kHz. 8-bit is also possible, but will result in 
considerably worse quality.

http://www.voip-info.org/tiki-index.php?page=Asterisk%20sound%20files

Any sample rate higher than 8 kHz would be useless because most POTS 
providers filter their calls at around 4 kHz anyway. The sample rate you 
need to encode a signal is (at least) twice the maximum singal 
frequence. This leads to a sample frequency of 8 kHz . I'm not sure if 
this is the reason why asterisk limits the use of wav files to 8 kHz. 
Since a phone line uses a 12 or 13-bit compressed signal at a sample 
rate of 8 kHz, using a higher frequency for wav files would imply the 
need to downsample on the fly. This could result in quite some 
performance loss.