Clipping audio with Plexamp on Raspberry Pi

Plex Labs
1

Running Plexamp v2.0 Beta 2 on Raspberry Pi 3 with HiFiBerry Digi+ Pro. I love it – it’s fab BUT:

On audio close to full scale there is noticeable distortion/clipping. The same audio file, played on the same system through the Plex web app, doesn’t distort.

I have tried with and without audio normalisation.

It’s not a generic Plexamp problem – playing the audio through Plexamp on a Mac is fine.

The files are Apple Lossless, 44.1kHz.

Has anyone else seen this? Any clues?

2

Not with Plexamp, but with LibreElec (and thus PMP embedded) I have found that I have to reduce the volume on the RPi by -1.3dB, or it will distort.
Most likely to happen if you go per HDMI to a TV from Sony and then from there per TOSlink to an amp.

3

So it looks like goofy maths in the Apple Lossless decoder (?). If I convert the files to wav then they play perfectly.

4

Wow, that’s pretty weird.

5

I set the alsamixer to -4db it’s a save bet.