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Topic: IMDCT not restore exact signal (Read 3114 times) previous topic - next topic
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IMDCT not restore exact signal

I code slow version of MDCT/IMDCT transformations by formula MDCT_EE5355.pdf and etrij.oct2013.0935.pdf (with KBD window)
I see, after reconstruction signal will not the same as input.  It does not look like a program error, the difference is that output signal fit to window - last value is near first value, it means, is possible doubling this signal and will be smooth.
I again MDCT this output signal and I see, spectrum MDCT is identical! Identical spectrum and different signals, because in signal is more information than in MDCT spectrum? This difference will be audible ?

IMDCT not restore exact signal

Reply #1 –
MDCT is not an orthogonal transform. A signal can only be reconstructed through an overlap-add process.

IMDCT not restore exact signal

Reply #2 –
This is my error: I test for sine signal length 3N, I badly apply second transformation to first, not second window. After correction signal is restoring perfect