[vorbis-dev] More mdct questions

[Dave, Anish]

> "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.

Yup, 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).

Hm.  I'll try to prove to myself that it really *is* the inverse.

> 
> > 
> > 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?

By FFT, I meant the FFT-method of solving the imdct equation (steps 1-8).
Sorry.

> 
> 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.

That would be *really* helpful, Monty.

> 
> > 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.

Yeah yeah, practice makes perfect.

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