The picture below shows a ADAU1401 eval board sending TDM audio to a ADAU1701 on a re-purposed prototype board. Four twisted pairs run the MCLK, BCLK, LRCLK, and TDM data between the boards.
Image may be NSFW.
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The received sound was erratic until I spliced a 150 ohm resistor into the yellow MCLK wire near its source end. The 1401's MCLK output has a lo-Z buffer which rings with the unterminated wire, as shown below, left. It looks much better with the resistor at right:
Image may be NSFW.
Clik here to view.
Image may be NSFW.
Clik here to view.
Thus it's a good idea to damp the MCLK signal between chips, especially when pcb traces or wires are long,
