[asterisk-users] T.38 (PRI) Fax Debugging

[Kevin P. Fleming]

On 07/20/2012 09:48 AM, Eric Wieling wrote:

Neither of your questions relate to T.38 :-) Maybe you meant T.30 instead.

> 1) Does anyone know of any software to debug the g711cap audio files Asterisk's res_fax generates?  Google has not been very helpful.

That will depend a lot on what you mean by 'debug'. We have found them 
useful to determine whether the audio path was 'clean' or not. For 
example, loading them into Audacity and looking at a spectral plot will 
tell you whether there were any extreme spikes, which usually are 
indicative of packet loss. You can also use them to look at the timing 
of the protocol interactions (delay between transitions between sending 
and receiving).

If your goal is to actually demodulate the audio into data and then 
interpret the T.30 transactions, I'm not aware of any easily available 
tools for doing that. Commetrex (the vendor of the FAX stack in 
res_fax_digium) has one that they use for helping to analyze problems, 
but I don't believe they make it available outside their company. There 
might be something in spandsp, but I haven't looked.

> 2) These files are in WAV format, but my Windows Media Player cannot play them. The Linux "file" command reports "RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 8000 Hz"  Does anyone have a solution?  Is it a bug?

I have never attempted to open them with Windows Media Player, so can't 
be of much help there. I know that Audacity will open them and play the 
audio properly, because that's what we used when we developed this 
'audio capture' feature.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
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