[Freeswitch-users] .wav vs .gsm file sizes for recording calls.

[Jan Berger]

A gentle warning when using GSM codec’s

 

Every codec compress voice at the cost of quality. And some codec’s like GSM
and G.729 are not a nice combination. If you use GSM to save disk space and
play it back using G.729 the resulting voice might contain some added noise
due to algorithmic incompatibility.

 

jan

  _____  

From: freeswitch-users-bounces at lists.freeswitch.org
[mailto:freeswitch-users-bounces at lists.freeswitch.org] On Behalf Of David
Ponzone
Sent: 24. juni 2011 23:42
To: FreeSWITCH Users Help
Subject: Re: [Freeswitch-users] .wav vs .gsm file sizes for recording calls.

 

Wes,

 

it's because you are confusing 2 things.

GSM is a codec, so it's a sound format.

WAVE is a kind of container (like MKV) that can contain various codecs.

In your case, you probably did a mistake using sox (it's not an easy tool),
so you ended up with a wav which is still GSM audio inside.

 

You have to tell sox which exact output format you want.

AFAIR, you have to use the -s option (for signed linear).

 

David Ponzone  Direction Technique

email: david.ponzone at ipeva.fr

tel:      01 74 03 18 97

gsm:   06 66 98 76 34

 

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Le 24/06/2011 à 23:26, Wes a écrit :





In my tests, if I record a call in .wav format, a 10 second file is 
about 177,000 bytes, while a 10 second .gsm file is 17,000 bytes.

I  then used sox to convert the .gsm file to a .wav file, and it stayed 
at around 17,000 bytes.  So, is the default recording format for .wav 
using a higher sample rate? vs the default conversion format for the sox 
tool?

checking the file type using "file" I see that the larger one is:
RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, mono 8000 Hz

and the wav created by sox via the default conversion from .gsm is:
RIFF (little-endian) data, WAVE audio, GSM 6.10, mono 8000 Hz

So apparently the larger wav file is 16 bit... how are these recording 
parameters controlled?  Can I set it to record directly into the smaller 
wav format? Or will I have to run sox on every file...

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