[Speex-dev] Speex newbie questions

Jean-Marc Valin Jean-Marc.Valin at USherbrooke.ca
Thu Sep 22 04:46:38 PDT 2005

> 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?

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?



Jean-Marc Valin <Jean-Marc.Valin at USherbrooke.ca>
Université de Sherbrooke

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