local channels and g729a voice quality

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Asterisk Users 4 Comments


We noticed a very sharp drop in voice quality when using digium g729a
codec. The problem seems to happen if the A channel (caller’s channel)
is a landline/mobile number contacted using the same outgoing provider
(as a local channel). It sounds like listening to a mono speaker on
low volume.

If I use a softphone that is directly registered to our asterisk box
the audio quality improves, the words come out more clearer and

I also asked my provider to test call me using their Cisco as5300
system and g729 codec and compared it with ulaw. The difference is

4 thoughts on - local channels and g729a voice quality

  • ^^ this doesn’t make any sense, the difference *should* be very much
    noticeable. g729 is a lower quality codec (in terms of audio quality).

  • You have conflated two very different things there – landline calls and
    cellular calls. A land line to a VoIP user by G.729A should sounds
    pretty good. A cellphone to a VoIP user by G.729A should sound *far*
    worse. Converting between two different low bit rate codecs really hits
    the quality, and all cellphone calls are low bit rate.
    You are conflating two things again. Quality and volume are largely
    independent issues.
    Try that again. If you really can’t hear the difference you should check
    carefully that the system is working as you think it is. If it is, maybe
    you should consult a doctor. G.729A is considerably poorer than ulaw.


  • Hi,

    I wasn’t aware of the difference in quality between landline and
    mobile phones, or that cellphones use a low bit rate.
    I did a test again, landline voice quality is better.

    From what you observed, how much drop in quality do I expect when
    switching from ulaw to g729 for a normal mobile-to-mobile call?