[asterisk-dev] $1000USD for fix of Asterisk g726-32 codec

[Daniel Silaro]

Steve,

Would it be enough to replace the Asterish g726 codec with your
version or does one have to install spandsp also?

On 5/21/06, Steve Underwood <steveu at coppice.org> wrote:
> Daniel Silaro wrote:
>
> > Steve,
> >
> > The current Asterisk g726-32 codec is functional and works ok for the
> > most part however it does give a distorted sound if you raise your
> > voice while speaking or if volume levels increase above "normal".
> > Switching over to g711 does not have this problem. Something is
> > clearly not right there with the codec implementation. If you have a
> > better g726 codec and you or someone else (I am not a programmer) is
> > willing to adapt/hook it into Asterisk I am willing to honor my offer
> > of $1000 USD.
>
> If it is only at high volume you might be hitting errors in the current
> G.726 code for Asterisk, or you might have a big DC offset in your
> signals. There shouldn't be any significant DC in a telephony signal,
> but there often is, and sometimes it is huge. A really big DC component
> upsets most simple lossy codecs, like G.711 or G.726. More complex lossy
> codecs tend to have their own internal way of coping with DC.
>
> Lets start with a correct implementation of G.726.
>
> Install a recent version of spandsp, such as
> http://www.soft-switch.org/downloads/spandsp/spandsp-0.0.2pre25/spandsp-0.0.2pre25.tar.gz
>
> Now replace the codecs/codec_g726.c file in your Asterisk source code
> with
> http://www.soft-switch.org/downloads/spandsp/spandsp-0.0.2pre25/codec_g726.c
>
> Rebuild Asterisk and see what happens. I haven't had time to test my
> version of codec_g726.c, but it compiles OK and it is very simple -
> there isn't a lot to go wrong. spandsp contains a test suite for the
> actual codec, which fully exercises it against the ITU test vectors, so
> the code that does the real work is well proven.
>
> If DC is the problem, I can add DC blocking to remove it.
>
> I thought Asterisk could use the 40k, 32k and 24k bps bit rates for
> G.726 these days, but having checked it seems it cannot. Only the G.726
> file format code allows for the various bit rates. My G.726 codec
> supports all the rates - 40k, 32k, 24k, and 16k - so adding support for
> all of them in Asterisk is pretty simple. It also supports compliant
> transcoding between G.711 and G.726, but I'm not sure how much work is
> needed to make Asterisk take advantage of that. Compliant transcoding
> significantly improves quality when you go G.711->G.726->G.711.
>
> Regards,
> Steve
>
>
> Regards,
> Steve
>
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