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How can I diagnose and fix this issue?

I have plugged my Samson Meteor USB mic into my Pi Zero W and run the ALSA arecord program. When I do, I get a low level "buzzing" that is quite audible in recordings; when I look at this in Audacity with the spectral filter, I see what one might expect: bands that fluctuate in frequency but not intensity, as would be expected for a sine or square wave, typically multiples of 500 Hz. When I repeat with my Pi 1 Model B, I get essentially the same thing, although it looks a little bit more like I see multiples of 800 and 4000.

By contrast, when I plug the mic into my laptop and record with arecord, I don't get this "buzzing".

Granted, I can filter out this interference in Audacity, but I wonder whether it might be possible to avoid the issue in the first place.

The first things that I tried were to move from a battery-powered Pi Zero W to a Pi Model B powered from a powered USB hub (and I connected the Pi and mic through the hub). That suggests to me that the problem is not likely supply-voltage fluctuation attributable to inadequate ability of the battery to supply power.

The next thing that I tried was to use an Adafruit USB isolator (Product ID 2107), but still the "buzzing" persisted.

From what I have observed above, I imagine that this issue may be caused by audio frequency interference traveling up the signal leads of the USB cable to the microphone and the microphone failing to prevent this interference from leaking to the input of the analog mic's pre-amplifier or the "microphone input" of the internal sound-card (the Meteor mic presents itself to the computer as a sound card, effectively a sound card to whose input the microphone is hard-wired). Of course, I can try introducing some kind of filter to block analog fluctuations on the USB signal leads, which might work if my hunch is right and if my filter does not degrade performance of USB signaling.

I would love to hear if anyone else has experience with problems of interference with the Meteor or other USB mics on the Pi and/or suggestions for how to proceed with diagnosing and fixing this issue.

Thank you.

  • I tried a different USB sound card - no buzzing. So, it would appear that, somehow, the Pi is doing something that the Samson Meteor mic doesn't like or refuses to deal with. It would be nice to be able to use my nice Meteor with my nice Pi ... – Art Oct 17 '18 at 12:26

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