I am using my pi as an audio server with MPD. I am using an USB sound card (C-Media chip) which works fine quality wise. However, every time the "ACT" LED comes on sound gets distorted with a popping/crackle noise. This is very audible especially in more slow songs and happens every few seconds (depending on what software accesses the SD card I guess).

Is this a known problem? I was unable to find anything for this specific problem on the web. Is this more likely an electrical "interference" of some sort, or a software problem? I am using pulseaudio for output.

Any pointers would be appreciated, as this makes the pi unusable as an audio server.

  • Does the USB-card work well in other computers? Do your power supply supply enough power? Jun 17, 2015 at 7:47
  • This seems to be connected to a general USB problem on the original Raspberry PI. See this thread for a long disucssion. Jun 19, 2015 at 13:24

1 Answer 1


I have heard that the Pi can give network problems as soon as the CPU must do some extra work. The solution was to use a power-supply that had more power. Perhaps your problem is related to that. A LED (or the process that makes the LED light up) does not consume much but perhaps just enough to have a hiccup in the USB.

  • No, it's actually related to well known USB problem, as I found out. Jun 18, 2015 at 8:22
  • @ShellfishGene If that were the problem (the pi's USB controller), everyone using a USB sound card would likely have it. However, while there are quite a few questions here from people who are using USB sound cards, none of them have mentioned this problem previously.
    – goldilocks
    Jun 19, 2015 at 14:37

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