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Thread: TDM using the odd channels for 24 bit audio

  1. #1
    Senior Member
    Join Date
    Aug 2016

    TDM using the odd channels for 24 bit audio

    I'm working on an 8x8 matrix mixer using my updated CS42448 board (see

    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 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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