[FFmpeg-devel] [PATCH] QCELP decoder

[Reynaldo H. Verdejo Pinochet]

Hello

Kenan Gillet wrote:

>>> +        if (lspf[9] > 1.0 - QCELP_LSP_SPREAD_FACTOR)
>>> +            lspf[9] = 1.0 - QCELP_LSP_SPREAD_FACTOR;
>>> +        for (i = 9; i > 0; i--) {
>>> +            if (lspf[i-1] > lspf[i] - QCELP_LSP_SPREAD_FACTOR)
>>> +                lspf[i-1] = lspf[i] - QCELP_LSP_SPREAD_FACTOR;
>>> +        }
>> this stuff has to be fixed before the patch can be commited, and yes
>> i would give you a hint how if i knew what is intended.
> 
> I am working on it. Unfortunately, I do not have any background in audio
> filtering so I am trying to make sense of the specs:
> http://www.3gpp2.org/Public_html/Specs/C.S0020-0with3Gcover.pdf
> 
> This particular part is on page 48, in section
> '2.4.3.3.1 Converting the LSP Transmission Codes to LSP Frequencies'
> 
> any help would be appreciated :)

Same page but section 2.4.3.3.2 The spread factor value
(.02) is used to guarantee a minimum separation between
the LSP freqs (80Hz). They are also required to be
ordered. Arguably this would, following the spec text,
produce a more stable and less sensitive to quantization
noise LPC filter. This is verbatim from the spec.

Bests
--
Reynaldo