[opus] MDCT implementation and his overlapped relationship

Jean-Marc Valin jmvalin at jmvalin.ca
Thu Apr 13 06:59:44 UTC 2017

Hi Diego,

You might find figure 3 or this paper useful:

It shows the MDCT window for a 5 ms frame, but the (non-zero) overlap is
always 120 samples regarless of the frame size. You can either see it as
partial overlap, or as a full-overlap with a window that has zeros on
the sides.



On 11/04/17 05:04 AM, Diego Alejandro Parra Guzman wrote:
> Dear all
> I'm working on the implementation of the MDCT for the processor
> ARM-Cortex-M4 I'm trying  to replicate the behavior of the MDCT
> for several overlapped values however I realized that current
> implementation of the MDCT is very close to the theory only in case in
> which we have and overlap exactly equal to N/2 where N is the size of
> the input vector as is shown in the examples  for celt.
> could you explain me if the implementation had been thought for
> different overlapped values, or instead the implementation uses only the
> overlap equal to N/2. 
> Additional I want to know in case of overlapped values different to N/2
> which values had been considered.
> Thanks for you support.
> -- 
> Diego Alejandro Parra Guzmán
> Estudiante de ingeniería electrónica
> Universidad distrital FJC
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