[FFmpeg-devel] PATCH: COOK audio decode infastructure to support fixpoint optimization

Michael Niedermayer michaelni
Sun Jul 15 20:13:38 CEST 2007


On Sun, Jul 15, 2007 at 07:59:22PM +0200, Benjamin Larsson wrote:
> > I guess you might be correct. Initially I was thinking we might be able to
> > use 16-bit ints to represent the signal and not 32-bits.  I'm still not sure
> > if the implementation requires the higher precision to be maintained does
> > anyone know if the algorithm requires the 24bits?
> > 
> Well what I meant was that I don't think 16 bits is enough for the
> transform step to keep a good enough precision. So if 32 bits is needed
> in the transform step then why not use 32bits in all the calculations
> for simplicity.

the general rule of thumb is that a n point decorrelation transform needs
log2(n)/2 bits more for the values in the frequency domain than in the
time domain

so 16bit is definitly not enough if you have 16bit audio


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Breaking DRM is a little like attempting to break through a door even
though the window is wide open and the only thing in the house is a bunch
of things you dont want and which you would get tomorrow for free anyway
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