Hi Frank,
A couple of comments/questiosn:
>
> :: Also, every transition from two different size windows is lossy. The
> :: MDCT is only lossless for overlapping windows of the same size.
> ::
> Is this a problem of bad designed (asymmetric) window functions or a
> problem of the MDCT (different from DCT).
>
It is a problem with all lapped transforms (like the MDCT).
You need at least a 50% overlap to get a lossless transform.
In AAC, a 1024 frame followed by a 128 frame, the 128 frame
will use a window of size 256, so it only extends 64 samples into
the 1024 frame.
>
> 4. The prefilter has a extremly short size of 4 or 5 TAPs, which is
> far below 128, 192, 576, or 1024.
>
>
If this is true, then the 1024 FFT should have plenty of frequency
resolution and the prefilter can be easily implimented via the FFT
coefficients. So no need for a new filter?
Mark
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