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MCHStreamer PDM Channel 3 always noisy 5 months 4 days ago #63526

  • marcpbcup
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I have a hardware module with 5 PDM MEMS Microphones coming into the MCHStreamer, using data lines (1+2), (3+4) and (5+6). One mic in each pair is tied to GND, the other High.  They all share a clock line, total wire length is around 30cm and scoped that clock looks good (no ringing, overdamping, etc), and data lines look good as far as I can tell.  Everything is working except line 3 is has a noise floor significantly higher than any other input line, on the order of -32dBFS while other lines are -80dBFS in a quiet room. It still receives signal if that signal is high enough above the noise floor. As far as I can tell this is a general MCHStreamer issue, as here's what I've tried for debugging:

- This has been the same on two MCHStreamer boards. 
- I can take my same mic array and plug it into an NXP DSP Eval board and there is no noise issue on any channel. 
- I can take one my mic pairs (3+4) and swap one wire to put it into line (7+8) and then there is no noise issue on (7+8). 
- I can take a different pair (1+2) and swap it into (3+4) and it has the noise issue on line 3. 


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