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I've been trying to set up audio playback on my Pi model B (running Raspbian, fully updated at the time of this posting), but I'm having issues with overpowering distortion. In the broader scheme I'm working on a Mopidy server, so I did what the first part of this guide suggests:

https://docs.mopidy.com/en/latest/installation/raspberrypi/#how-to-for-raspbian-wheezy-and-debian-wheezy

Basically I set the audio output to the jack (instead of the HDMI output, and then tried to play a test sound:

sudo amixer cset numid=3 1
aplay /usr/share/sounds/alsa/Front_Left.wav

The result was an ear-splitting, high-pitched modem sound. I could hear the test sound being played in the background, but it was much quieter than the noise. Oddly enough, the noise didn't stop playing after the test file was done playing; the only thing that got rid of it was a reboot.

I read somewhere that power supply noise might be an issue, but switching to a higher-quality supply and cable didn't seem to do anything. I also tried adding a ferrite bead to the supply line, but it had no effect. I can't seem to find anyone with a similar problem, so at this point is it safe to assume that my Pi is damaged? What else could cause this behavior?

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Well, it looks like I found the problem. I happened to be running richardghirst's very fine ServoBlaster software to control some PWM devices from a previous project, and I forgot that it can interfere with sound output in some situations.

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