[Asterisk-Users] Amazing, great protocol IAX

[Steve Underwood]

Adam Hart wrote:

> Thomas Hutton wrote:
>
>  > A) Which is better sound quality in this situation?
>
>> On a local net (100 megabit) my SIP phone talks to Asterisk running on
>> my firewall.  I only have 128K upload (sometimes) on my fricken
>> Third-World DSL connection so I want to use GSM or ILBC going out over
>> IAX2.  Should I let the DSP in the phone talk to asterisk in ULAW or
>> ALAW, having Asterisk translate to GSM or should I force the phone to do
>> it in the lower bandwidth codec?  I honestly can't tell a difference in
>> quality or latency.  I'm not real impressed with the Grandstream
>> Handytone 286 because it doesn't have GSM - so I'm stuck trying to
>> compare straight through ILBC to translated GSM.  Any fine tuning codec
>> advice would be appreciated.
>>
>
> Why do you need GSM at all, just keep everything iLBC. Asterisk won't 
> have to transcode and it will sound much better

As a general point, transcoding any low bit rate codecs can loose 
considerable quality. Even low bit rate -> linear -> original low bit 
rate can loose quite a bit in quality, so just editing a low bit rate 
audio file typically makes it sound worse. Wherever practical avoid 
transcoding. It saves MIPs, it save quality, it is good and wholesome. :-)

Regards,
Steve