Speex dev - Aug 2006 - Historical question

Hello Jean-Marc and all,

I recently had a talk with somebody about CELP. He said, there is this
federal standard 1016 (4.8kbps) with a reference implementation of the
Department of Defense (only on Sun, unfortunately, if I got this right).
This one is noticed in the manual already.

He also said, since there is this implementation of the DoD, nobody
would voluntarily re-implement CELP.

If I read the manual, I guess you just took the idea names CELP, did
some conceptual work (resulting in NB, WB und UWB mode as well as all
these bitrates Speex supports, as well as stuff like frame-length and
number of subframes) and then actually made a new implementation (DoD
CELP is far less than Speex).

So the Question is: did you take any code from DoD CELP?
What would happen, if I took a 8kHz-Wav file and did
	speexenc -n -.bitrate 4800 file.wav file.spx
Would the result of this be comparable to a DoD-CELP encoded file?
Besides all the other bitrates and sampling-rates, how does speex differ
from DoD CELP (I unterstand Speex is using frames of 20ms with 4
subframes, DoD CELP uses 30ms frames with 4 subframes, but this is about
it what I know)?
Does Speex extend DoD CELP or does it only pick up the same idea (CELP)
and has nothing more to do with DoD CELP?

Ciao,

Bj?rn


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> I recently had a talk with somebody about CELP. He said, there is this
> federal standard 1016 (4.8kbps) with a reference implementation of the
> Department of Defense (only on Sun, unfortunately, if I got this right).
> This one is noticed in the manual already.
I think DoD CELP can be compiled easily under any OS.
> He also said, since there is this implementation of the DoD, nobody
> would voluntarily re-implement CELP.
What do you mean here?
> If I read the manual, I guess you just took the idea names CELP, did
> some conceptual work (resulting in NB, WB und UWB mode as well as all
> these bitrates Speex supports, as well as stuff like frame-length and
> number of subframes) and then actually made a new implementation (DoD
> CELP is far less than Speex).
CELP is a very broad technique. Nearly all modern speech codecs use a
variant of CELP. 
> So the Question is: did you take any code from DoD CELP?
No, because 1) it's an old standard with very different goals and 2)
there would have likely been legal issues.
> What would happen, if I took a 8kHz-Wav file and did
> 	speexenc -n -.bitrate 4800 file.wav file.spx
> Would the result of this be comparable to a DoD-CELP encoded file?
Speex only has a 3.95 kbps and a 5.95 kbps mode, so comparison is
difficult. I haven't listened to DoD CELP much, but I would assume that
Speex 5.95 would be much better. I don't know about Speex 3.95 kbps.
> Besides all the other bitrates and sampling-rates, how does speex differ
> from DoD CELP (I unterstand Speex is using frames of 20ms with 4
> subframes, DoD CELP uses 30ms frames with 4 subframes, but this is about
> it what I know)?
Outside of the general CELP Analysis-by-Synthesis principle, I'd be
surprised if Speex shared much with DoD CELP. One of the key aspect in a
CELP codec is the quantization of the innovation (fixed codebook) and
Speex is different from any other speech codec that I'm aware of.
> Does Speex extend DoD CELP or does it only pick up the same idea (CELP)
> and has nothing more to do with DoD CELP?
Completely independent.

	Jean-Marc