>
> Hi Gaby
>
> > Why can we read in the litterature that humans got 25 CB but mp3 uses only
> > 22?
>
> let us try to get it in order:
>
> bark scale is used by the spreading function
> Bark 0 : 0-100 Hz, Bark 24: 15.5 - 20.4 kHz
>
> masking is calculated for convolution bands
> Lame uses 64 equidistant convolution bands from 0 Hz up to Nyquist
>
> each of the 22 scalefactor bands is responsible for a group of
> subbands (the convolution bands), but we have only 21 scalefactors
> (12 scalefactors w/ short blocks)
>
>
> Ciao Robert
>
Some more info:
Barks, as used in mp3, is just a different way to measure
frequency. The conversion is givin in freq2bark() in util.c
There is nothing magic about 22 or 25. The important thing
is that the bands have about the same width when measured
in barks. In MP3, each band is about .9 barks, and AAC,
each band is about .5 barks. (AAC has 49 bands, IIRC).
MP3 and AAC psycho acoustics actually computes everything
in bands of about .33 barks wide (the 64 convolution bands
Robert mentioned), and then this information
is mapped to the 22 scalefactor bands.
Mark
--
MP3 ENCODER mailing list ( http://geek.rcc.se/mp3encoder/ )
