[asterisk-users] Meetme replacement with native 729 support

[Tilghman Lesher]

On Tuesday 15 July 2008 14:24:30 John covici wrote:
> on Tuesday 07/15/2008 Tilghman Lesher(tilghman at mail.jeffandtilghman.com)
> wrote
>
>  > On Tuesday 15 July 2008 13:32:12 Artie Gold wrote:
>  > > Does anyone know of a replacement for meetme that provides native G729
>  > > support? The transcoding back and forth from/to 711 is eating too much
>  > > processor for what we're doing...
>  >
>  > Buy a hardware transcoder board.  There is simply no way to mix
>  > compressed audio like that without decompressing first.
>  >
>  > And by the way, it's decompressing to signed linear 16-bit audio, not
>  > ulaw. Even mixing of ulaw requires a decompress to signed linear.
>
> OK, I guess I need to show my ignorance -- what is the difference
> between ulaw and signed linear?

ulaw is a compression algorithm which compresses the 16-bit 8000Hz
signed linear (slin) format down to 8-bits per sample.  So while signed
linear consumes 128kbps, ulaw only consumes 64kbps.  Ulaw is actually
a fairly simple coding algorithm, and it compresses from and decompresses
to slin with a 1-to-many lookup table between the values.  So it's pretty
fast, as implemented.

A more technical explanation can be found on Wikipedia, if you are so
inclined:
http://en.wikipedia.org/wiki/Μ-law_algorithm

-- 
Tilghman