[vorbis-dev] More mdct questions

[Segher Boessenkool]

"Dave, Anish" wrote:
> 
> Hey thanks for your help!  Your equation works.  It's the same as the one

Which one? I guess the +2N one.

> given in the eusipco.corrected.ps document minus the 4/n term outside the
> summation.  So was that (4/n) term the typo in the document?

It's not a typo. The 4/N is necessary to make the backward transform a true
inverse to the forward transform; otherwise, it will have a N/4 scaling. But
scaling is not a problem for our purposes, so it's omitted (or maybe it is
fused with the window multiply; don't know it off my head, and much too lazy
to look it up).

> 
> Are there any typos in the FFT algorithm described?  If so, what are they?

I wasn't aware there is a FFT algorithm described in the Eusipco document?

Maybe Monty can answer what the typos are; there are a few obvious
typos, but
even then it won't work. So I guess Monty found the non-obvious (to me)
typo(s) as well.

> I wasn't able to tell by comparing the vorbis code to the algorithm in the
> paper (I'm not a dsp/fft/dct guru).

The skills you need are a lot of programming experience, so the code is just
like your native tongue to you; and some fluency in algebra and calculus.

Ciao,

Segher

> 
> Thanks!

Hey, I ask so much, want/need to help as well ;-)

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