[asterisk-users] Meetme replacement with native 729 support

[John covici]

on Tuesday 07/15/2008 Tilghman Lesher(tilghman at mail.jeffandtilghman.com) wrote
 > 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/?-law_algorithm

OK, thanks -- I was a bit puzzled because if I want to play audio over
asterisk, it has to be 16-bit 8khz signed, so that is what I thought
ulaw was -- thanks for the clarification.

-- 
Your life is like a penny.  You're going to lose it.  The question is:
How do
you spend it?

         John Covici
         covici at ccs.covici.com