Speex dev - Sep 2005 - Speex newbie questions

Hi everyone,

I have got some questions about Speex, I am sorry if my questions are too 
newbie:

1. For the LP analysis, did Speex use the AR (Autoregressive) model or the 
ARMA model?

2. Am I right to say that Speex use a multistage VQ (since I believe Speex 
employs two or more VQ consecutively - based on the manual it says that 
Speex uses dynamically selectable codebooks (linear prediction,pitch 
prediction and innovation))?

3. It is said in the manual that Speex also use sub-vector fixed 
(innovation)codebooks, does this mean that it also utilises a Split VQ?

4. In the part about innovation codebook, it is said that the final 
excitation signal would be made up of the innovation signal and the pitch 
prediction, I presume that by final excitation signal it meant the output 
signal that Speex will produce (Is this correct btw?) but what does 
innovation signal refers to? It is said that it represents information that 
couldn't be obtained from either linear prediction and pitch prediction, but
what is it actually? (I have tried to look at the code, but I am not that 
good at reading codes)

5. Speex is a CELP-based coder, so I believe that it utilises both Spectral 
analysis and Fourier analysis (FFT) during the LP analysis, Am I right?

Once again, I am very sorry if my questions are too newbie , Thank you very 
much for your time.

Leonard

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> 1. For the LP analysis, did Speex use the AR (Autoregressive) model or the 
> ARMA model?
AR
> 2. Am I right to say that Speex use a multistage VQ (since I believe Speex 
> employs two or more VQ consecutively - based on the manual it says that 
> Speex uses dynamically selectable codebooks (linear prediction,pitch 
> prediction and innovation))?
No.
> 3. It is said in the manual that Speex also use sub-vector fixed 
> (innovation)codebooks, does this mean that it also utilises a Split VQ?
sub-vector==split as far as I'm concerned.
> 4. In the part about innovation codebook, it is said that the final 
> excitation signal would be made up of the innovation signal and the pitch 
> prediction, I presume that by final excitation signal it meant the output 
> signal that Speex will produce (Is this correct btw?) but what does 
> innovation signal refers to? It is said that it represents information that
> couldn't be obtained from either linear prediction and pitch
prediction, but
> what is it actually? (I have tried to look at the code, but I am not that 
> good at reading codes)
innovation = fixed codebook
output = 1/A(z) * (pitch_prediction + innovation)
This is true for any CELP codec (by definition).
> 5. Speex is a CELP-based coder, so I believe that it utilises both Spectral
> analysis and Fourier analysis (FFT) during the LP analysis, Am I right?
No.

	Jean-Marc

-- 
Jean-Marc Valin <Jean-Marc.Valin@USherbrooke.ca>
Universit? de Sherbrooke