Choppy sound files

Hi All,

I have three “white noise” MP3 files that I am playing with Asterisk. When calling via an ITSP it is fine. When calling from Sprint or Ooma the quality is real bad. I assume it has to do with the frequencies of the white sounds. I can blame it on their routes but it won’t help fix it. What format would be the best one to stream such sounds? I will also add that other “regular” recordings sound fine. The calls are coming in over G711U. If you want to hear a sample of the files please let me know.


ulaw (i.e. no real time transcoding)

slin and wav (lower case) are also cheap to convert to mu-law, and do not introduce any quality loss over that intrinsic to the use of mu-law. Note that mu-law is likely to be in use on the PSTN, so there is no point in using any higher a quality codec for calls that can terminate on the PSTN.


I tried:
mp3 (original format)

As I wrote above I assume the reason for the crappy sound is the frequency limit of the PSTN (8 khz). What format should I capture it in to get the best possible result?

The frequency limit of the PSTN is 3.4kHz (4kHz from Nyquist for 8kHz sampling, with additional margin for anti-aliasing filters).

Choppy audio is usually caused by jitter (e.g. overloaded network, overloaded CPU, or trying to run on a VM without a sufficiently low guaranteed maximum scheduling latency).

The PSTN uses G.711 mu or G.711 A, depending on your country.


All of what you are saying I know. My question is whats the best way to play such sound files.

I converted the files from mp3 to ulaw and it has the issue. Perhaps I should capture it in another format or it wont matter because the sampling will always be 8,000

More likely the problem is not codec related.

Are you running on VM?

Incidentally, white noise will likely be handled very strangely by MP3. It is not at all a good match for its standard algorithm, so might just send: there is white noise here.