Troubles with Psy Model

I’m battling with psychoacoustic model. 3GPP TS26.403 seemed clear at the start but then problems have begun.

The main problem is perceptual entropy estimation. Since MDCT coefficients differ by magnitude in FFmpeg and 3GPP, perceptual entropy estimated by formulae from 3GPP differs much from actual number of bits to code. Also 3GPP encoder always makes scalefactor lie in range 104…164, beats me why (and its center does not correspond to scale = 1.0 either).

I have to investigate further before continuing work on psy model. I also hope to see AAC decoder in FFmpeg SVN soon and push my work on encoder there as well.

2 Responses to “Troubles with Psy Model”

  1. Ilnar says:

    Hi, Kostya.
    Glad to see that somebody works on AAC.
    I have a few questions if you don’t mind:
    Do you know if development around of AAC will be only during this summer or there will be some constant work? Is there possibility that new AAC encoder will have enough good psy model to be at least comparable to Nero or Apple encoders?
    Thank you and good luck.

  2. While producing quality similar to Nero or Apple would be hard considering that they have some people working full time on this, I think that better quality than FAAC would be a good and realistic target.