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

[Marc Hoffman]

On 7/15/07, Michael Niedermayer <michaelni at gmx.at> wrote:
>
> Hi
>
> 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


Agreed. so whats your take on 16bit phase factors?