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

[Steve Underwood]

Daniel Silaro wrote:

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

You need to install spandsp to use my code. What I have provided in 
codec_g726.c is a thin layer to access the G.726 codec in spandsp itself.

I missed in step in my last email. 
http://www.soft-switch.org/downloads/spandsp/spandsp-0.0.2pre25/codecs_Makefile.patch 
contains a patch for the codecs/Makefile. This patch needs to be applied 
before rebuilding Asterisk.

Regards,
Steve

>
> 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
>