[asterisk-users] Codec Conversion

Jeff Brower jbrower at signalogic.com
Fri Aug 6 03:43:33 CDT 2010


>   On 08/06/2010 05:40 AM, Jeff Brower wrote:
>> Miguel-
>>> El 05/08/10 14:50, Tim Nelson escribió:
>>>> ----- "michel freiha"<michofr at gmail.com>  wrote:
>>>>> Dear Sir,
>>>>> I tried to convert ilbc to ulaw and get the same result...Bad Voice
>>>> Quality
>>>>> Regards
>>>> Again, iLBC is poor quality to begin with. You can't take a poor audio
>>>> sample and make it better by converting it to a codec with better
>>>> 'resolution'. An audio sample full of robot voice is going to sound
>>>> like the same robot voice even if you transcode it to a better quality
>>>> codec, whether that is G.729, G.711u, or the latest 'HD Voice' codecs.
>>>> --Tim
>>> This just made me remember some comment on the iax.conf sample file...
>>> disallow=lpc10            ; Icky sound quality...  Mr. Roboto.
>> LPC10 is a very old codec, from early 1980s.  LPC10 doesn't do a good job with pitch detection so it tends to have a
>> 'robotic' sound.  With advent of MELPe, anyone needing bitrates 2400 or less should not be using LPC10.
>> -Jeff
> MELPe is patent encumbered,

Not if used for govt/defense purposes.  For commercial-only purposes, TI will waive royalty fees if their chip is used
in the product.  It would have been nice if Digium had considered the many advantages of using a DSP pioneer such as
TI before putting a Mindspeed chip on their TC400B card.

> so there is still a place for LPC10 [...]

I haven't seen an LPC10 implementation with MOS higher than 2.5.  Due to its age and expiration of patents, LPC10
might be a basis for a 2400 bps open source codec.  But enormous improvement would be needed to come close to MELPe


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