I'm trying to build up a recording station using a Raspberry pi 3B. I soldered four mics (two per channel) to a stereo jack and plugged it into the "external mic" audio input of the Zoom H1. Then I connected the Zoom H1 to the Raspberry using a USB cable, and here's the problem: I get a constant and annoying noise on both channels, but especially in the first one (left I guess?), or, in general, I don't get the same disturbance in both channels. Here's an example:

Audio file

Channel 1 Channel 1

Channel 2 Channel 2

Also, I don't know what's the strange "volume adjustement" (those dark bands that get wider) at the beginning of every recording (using arecord).

Here are a few things I can say about it:

  • There're no problems with the mics (they're properly connected). If I don't connect the Zoom H1 to the Raspberry and I power everything with a battery I don't get any disturb.
  • Nothing's wrong with the Zoom H1. I also tried with the Zoom H1n, and I got the same problem.
  • No power deficit. With the Zoom H1n there's the option to power it with the battery, instead of taking the current from the USB cable. Even doing so, the problem still remains.
  • Raspberry is not defective. I get the same problem also with another Raspberry pi 3B+.
  • The problem is not due to the recording program of Raspberry (arecord). I can hear the noise also by listening in "monitoring mode", with putting the headphones' jack in the Zoom H1's audio output and listening what comes in.
  • The use of internal mics avoids it. If I record with the built-in mics of the Zoom H1 I get rid of the noise.
  • Connecting the Zoom H1 to my laptop also avoids it. If I connect the Zoom H1 by USB to my laptop I get rid of the noise.

That said, I don't know whether this is a Raspberry's or a Zoom H1's configuration problem...

Thank you in advance! :)

  • Do you get the noise when connecting the Zoom H1 to the laptop AND have the raspberry pi running near the external Zoom H1 mics? If so a shielded metal case for the Raspberry pi might help.
    – Craig
    Commented Aug 20, 2020 at 22:01
  • The mics are always at the same distance quite far apart, there shouldn't be interference from the Raspberry pi. If I take the the Zoom H1 closer to the Raspberry while connected to the laptop, I can't hear any difference...
    – plaf2000
    Commented Aug 22, 2020 at 23:28
  • I connected the ground from the AC power plug to the microphone ground and I got rid of the noise.
    – plaf2000
    Commented Aug 24, 2020 at 19:09
  • I moved the USB connector from adapter to RPI USB port. The 50Hz sound disappeared. This works for 5V powered audio. Some countries use 60Hz power supply. Commented Jan 4, 2021 at 15:32
  • @DanFroberg I'm sorry, I'm not sure if I get what you mean... What do you mean with "adapter"? Here in Switzerland the power supply should be 50Hz, so I don't know if that could be a problem... Thanks! As I wrote months ago, I've been able to get rid of the main disturbing noise, but I still feel like the audio is not 100% clear, so I'm still trying to understand what's wrong.
    – plaf2000
    Commented Jan 5, 2021 at 17:03


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