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Topic: different peak values in PQMF/MDCT transform in MP3 or self implemente (Read 1900 times) previous topic - next topic
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different peak values in PQMF/MDCT transform in MP3 or self implemente

Hi all,

This topic is about PQMF - MDCT conversion in MP3 (LAME was used)
I've done 3 things which should have (to my knowledge) given the same outcome, but then gave some phase shifts instead..

wave file used: 345hz single tone lasting for 1 seconds

the 3 diagrams shown below are the peaks for each 576 samples over a second. Hence 44100/576 peaks are found in the diagram.


1. by applying 576 point MDCT on the pure waveform (in matlab)



2. by extracting out mdct_enc variable in LAME ( i presume that's the mdct values after PQMF and MDCT has been implemented on the waveform



3. by extracting out the PQMF values (sb_sample) in the LAME encoder and perform a 18 point mdct on each sub bands through Matlab




please point out if my values PQMF/MDCT are wrong, anyone has an explanation for the 'phase lag' ?

thank you for any suggestions!

tubanana

 
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