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I encountered a really odd behaviour with my Raspberry Pi B+, running a slightly modified version of Raspbian with a PiTFT screen from Adafruit. Because the screen cannot access the GPU I dialed down the GPU memory as low as it would go during installation (4 MB I think?).

I wanted to use the system as a portable music player, but I found the audio playback was extremely poor (constant skipping). I tried changing the GPU memory split to 32 MB, and all of a sudden the playback was completely smooth.

I thought that the GPU was primarily used for handling calculations performed while rendering 3D graphics. Why would it affect audio playback this noticeably?

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  • What audio player did you use?
    – goobering
    Commented Mar 27, 2016 at 22:15
  • cmus, moc, and a few others, but the behaviour was consistent across different programs. Commented Mar 27, 2016 at 22:17
  • Did you try omxplayer? Commented Mar 28, 2016 at 0:39
  • With mpg321 and my GPU memory set to 0 I have perfect playback. Commented Mar 28, 2016 at 1:31
  • The last I read the minimum settable GPU memory was 16MB - I think if you set it lower than that it's still rounded up to 16MB.
    – goobering
    Commented Mar 28, 2016 at 8:07

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The Raspberry Pi sound system is controlled by the GPU, both for HDMI and analog audio output. An interesting detail are the noise shaping algorithms running on the GPU for analog output. Quite a bit of engineering went into them, seeing that the analog audio hardware itself is quite poor.

Sources:

"Analogue Audio testing" raspberrypi.org
"Analogue Audio redux" raspberrypi.org

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