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Thread: TDM using the odd channels for 24 bit audio

  1. #1
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    TDM using the odd channels for 24 bit audio

    I'm working on an 8x8 matrix mixer using my updated CS42448 board (see https://forum.pjrc.com/threads/58836...ed-performance)

    As per the instructions I'm only using the even TDM channels.

    I'm wondering whether there's any intelligence in the odd channels that can be used to regenerate 24 bit audio. I seem to remember a comment somewhere that the odd channels contain the low 8 bits shifted up, but can't find it again now.

    It wouldn't take much effort to convert macaba's crosspoint mixer code https://forum.pjrc.com/threads/43752-Crosspoint-Mixer? to TDM x 16 : 8 x 24 bit matrix : TDM x 16, as long as there's no other processing to be done.

    Just connecting the odd channels across from TDMin to TDMout doesn't seem to change much:

    24 bit (odd and even) Rightmark results (the THD + N figures are anomalous, as I had the input level at the onset of overload to maximise dynamic range. With the input 3 dB lower, THD+N is at -95dB):
    Click image for larger version. 

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    16 bit (even only):
    Click image for larger version. 

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    BTW, straight through, my Focusrite audio interface has more dynamic range, so I'm not caught with its limitations.
    Click image for larger version. 

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    Last edited by palmerr; 08-03-2021 at 12:25 AM.

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