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audio transcoding

Started by DragosD December 21, 2005
Hi all,

I was wondering if anyone can give me some information (links, forums,
possible books) on audio transcoding topic. 
I've been assigned this task and I need a starting point.
I'm generally interested in audio transcoding but more specific in 
G.729.A or G.729.AB to G.723.1A transcoding.

Now the trick is the transcoding path should be direct without going
through G.711

Many thanks


Transcoding is an interesting subject, and does not need to go through 
G711 (u-law-, A-law) at all.  I am assuming you meant PCM samples, i.e. 
a tandeming process of decompression & recompression.  Doing that 
correctly is very beneficial for todays networking world which may 
combine different networks & standards at the same phone call, and for 
conferencing and mixing.  It is yet another "black magic" :)

There are several ways of doing that.

1. When dealing with Analysis-by-Synthesis (A-b-S) type coders such as 
G.729 & G.723.1, the transcoding may be performed in various A-b-S ways 
for best performance, but may also be done otherwise in open-loop or 
hybrid methods.

2. For parametric coders such as MELP or MELPe, parametric transcoding 
may be done in open loop and yet achieve very good performance.  For an 
excellent practical implementation of parametric transcoding you may 
refer to its implementation in the MELPe standard:
http://www.MELPe.com
http://www.Compandent.com/melpe_faq.htm
http://www.Compandent.com/products_melpe.htm

Parametric transcoders are available there, between the MELPe rates of 
2400, 1200 and 600 bps, and between MELPe and other parametric vocoders.

Very efficient multi-channel implementations (5%-15% CPU) are also 
available for PC & Workstations running under Windows, Unix, Linux, 
MacOS etc.., in addition to a wide variety of multi-channel DSP 
implementation such as TMS320c54xx, TMS320c55xx, TMS320c64xx, OMAP etc..

Check up with Compandent, they have the speech coding expertise needed 
to provide you with the right answer & solution!

Cheers,
NS

DragosD wrote:
> Hi all, > > I was wondering if anyone can give me some information (links, forums, > possible books) on audio transcoding topic. > I've been assigned this task and I need a starting point. > I'm generally interested in audio transcoding but more specific in > G.729.A or G.729.AB to G.723.1A transcoding. > > Now the trick is the transcoding path should be direct without going > through G.711 > > Many thanks > >