[vorbis-dev] More mdct questions

[Segher Boessenkool]

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

You need to take the window and the overlap/add into account to have it
an inverse. You don't need the precise shape of the window; only two facts:
1) it has to be symmetric, and
2) the sum of the squares of the overlapping windows has to be 1.

> > > 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.

You mean a fft-like method; these are called _fast transforms_. There are
more fast transforms than just the fast Fourier transform: the FHT (fast
Hartley transform, no multiplications needed), etc.

It is also possible to calculate DCT/DST/MDCT by doing some simple preprocessing,
doing a FFT, and then doing some simple postprocessing.

> > 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.

Pactice makes less imperfect |-}

Ciao,

Segher

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