Just a small article to explain how to fix the annoying "cracking music" that I had when I was playing 5.1 albums on my RPi.

At first I though it was a resampling issue (converting from 44100Hz to 48000 or 96000Hz or vice-versa) or a bug in Alsa. but it turn out that you have to configure your HDMI output to a 7.1 configuration (8.1), I found the solution on this forum.

So here is my \etc\asound.rc file:

pcm.device{
    type hw
    card 0
    device 0
}

pcm.!surround51 {
    type route
    slave.pcm "device"
    slave.channels 8
    ttable {
      0.0 1
      1.1 1
      2.4 1.8
      3.5 1.1
      4.3 1.8
      5.0 0.5
      5.1 0.5
      6.6 0
      7.7 0
    }
}

Here I reroute also my channels differently and I have specific volume level for some of them. My speakers are positioned at different places in my room, so I had to adjust that. Feel free to customize it regarding your own configuration.

As you can see the speaker 6 and 7 are muted. It's a 7.1 setup but behaving like a 5.1. The LFE channel is send to my two main column speakers that can do low frequencies. If you have a subwoofer you can route the channel 5 directly to it.

I also added another virtual device to upmix stereo output to all my speakers:

pcm.20to51 {
  type route
  slave.pcm surround51
  slave.channels 6
  ttable.0.0 1
  ttable.1.1 1
  ttable.0.2 1
  ttable.1.3 1
  ttable.0.4 0.5
  ttable.1.4 0.5
  ttable.0.5 0.5
  ttable.1.5 0.5
}

And in MPD I added two new output, one for the direct 5.1 configuration, one for the stereo to 5.1 virtual device:

audio_output {
        type            "alsa"
        name            "Ampli 5.1"
        device          "surround51"
        format          "96000:24:6"
        auto_resample   "no"
}

audio_output {
        type            "alsa"
        name            "Ampli Stereo to Surround"
        device          "20to51"
        format          "96000:24:2"
        auto_resample   "no"
}

I set the bitrate and sampling to 24bit and 96000 to prevent some downsampling (I have some high quality audio albums in 96Khz/24bit FLAC format).

That's all folks !

#raspberrypi #rpi #music #mpd #alsa #surround #stereo