Asterisk MoH Sound Quality

Posted on 2008-06-19
Last Modified: 2013-11-12
Every time I convert either a WAV or MP3 file to GSM using sox the sound quality drops drastically.  I have even tried to convert the file to GSM using an audio converter but stil no luck. Our PBX is asterisk v1.2 based.  Any suggestions on how to make Music on Hold not sound like it is distorted?  Thanks in advance.
Question by:sharpC
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LVL 36

Expert Comment

ID: 21829089
If you playback the converted file on a pc does it sound correct?

Have you tried reducing the volume during the conversion process?
Normally on hold music is quieter than voice so it is normal to reduce the volume.

Author Comment

ID: 21830954
On my pc recording sounds great.  And yes, I have tried reducing the volume.  In addition, I have tried saving it to various file formats using Adobe Audtion but still sounds like my sound clip has become synthesized.  Any other suggestions?
LVL 36

Expert Comment

ID: 21831222
gsm is a compressed format so it wont sound perfect. Certenly if you are listening to it on a pc it will be a vast difference in quality. Using a telephone handset it should be less noticeable though.

Maybe gsm is not the best format. Over what sort of connection are people going to be hearing the music on hold?
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Author Comment

ID: 21832546
I "think" you are asking me about my PBX.  We use an asterisk v1.2 server connected through a T1. Sorry if I am being dense.
LVL 36

Expert Comment

ID: 21832748
Is the T1 offering a primary rate telephone service or are you using voip over it?
If you are using voip do you know what codec you are using? (ulaw/alaw (g711), gsm, g723 etc...)

Author Comment

ID: 21856823
I had to verify settings with our vendors.  T1 is VoIP and our PBX is using:     G711 codec to transmit audio.  In the case of remote users where the Low Bandwidth Codec option is checked, the pbx will use the G729 codec
LVL 36

Accepted Solution

grblades earned 125 total points
ID: 21858034
In that case I would not convert it to gsm format. You are just converting to a lower quality more compressed format which asterisk will have to decompress to g711 or decompress and recompress back into g729.

You would be best off converting to .sln format (which us basically g711) using the instructions at :-

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