[vorbis-dev] mdct question

[Segher Boessenkool]

Hi Dave, list,

"Dave, Anish" wrote:
> 
> Hi,
> 
> Can someone tell me which MDCT and invMDCT equation uses?  I implemented the

It just a normal shifted mdct, like the one used in mpeg layer 3.
it's equations are:

(time domain: a_j, freq domain: b_k; w_j is the window)

forward:

b_k = sum(j=0..4N-1) a_j * w_j * cos( (2k+1)(2j+1+-N) / 8N )

a_j = w_j * sum(k=0..2N-1) a_j * cos( (2k+1)(2j+1+-N) / 8N )

where +- means: I'm not sure whether it is + or -, but I think it is +
(forward as well as backward).

k is 0..2N-1, j is 0..4N-1.

Ciao, hope this helps,

Segher

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