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Surround Sound on a Raspberry Pi 3 2024-10-06Permalink

In this post, we are going to cover how to play videos on a Raspberry Pi 3 with multiple audio channels (i.e. 5.1 Surround Sound) over the HDMI port.

By default, a Raspberry Pi 3 uses ALSA for audio, and we'll assume you're using that instead of PulseAudio.

Installing VLC

First up, we are going to need to install vlc to play videos and audio from the command line, as the old omxplayer is deprecated:

sudo apt-get install --no-install-recommends vlc-bin vlc-plugin-base

The command above will not install the vlc-plugin-qt package, which I think is good for a headless setup of VLC. We only care about running vlc from the command line.

Configuring HDMI settings

The next step is setting some configuration in /boot/config.txt for the Raspberry Pi. Here are the relevant entries in my file:

# Stop rPi from sending active source message over CEC at start-up 
hdmi_ignore_cec_init=1

# Pretends CEC is not supported at all by TV.
# Ignoring CEC prevents weird situations where the rPi wants to set itself
# as the active source when the receiver is turned on
hdmi_ignore_cec=0

# Enable audio (loads snd_bcm2835)
dtparam=audio=on

The only important line is this one dtparam=audio=on. The others are just nice when your Raspberry Pi is connected to a TV or receiver.

Configuring ALSA

Next, we need to modify either /etc/asound.conf or ~/.asoundrc. I prefer modifying the latter. Here's what it looks like:

pcm.!surround51 {
	type route
	slave.pcm "hw:0,0"
	slave.channels 8
	ttable {
		0.0= 1
		1.1= 1
		2.4= 1
		3.5= 1
		4.3= 1
		5.2= 1
		6.6= 0
		7.7= 0
	}
}

This creates a device called surround51 that sends 6 channels of audio to hw:0,0 under the hood. You need to ensure that hw:0,0 is the HDMI audio device. Check this with aplay -l. Here's what I get on my system when I run aplay -l:

**** List of PLAYBACK Hardware Devices ****
card 0: b1 [bcm2835 HDMI 1], device 0: bcm2835 HDMI 1 [bcm2835 HDMI 1]
  Subdevices: 4/4
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
  Subdevice #3: subdevice #3
card 1: Headphones [bcm2835 Headphones], device 0: bcm2835 Headphones [bcm2835 Headphones]
  Subdevices: 4/4
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
  Subdevice #3: subdevice #3

For some folks, you may need to use hw:0,1 instead. On my system, I have already used raspi-config to set the HDMI port as the audio output instead of the 3.5" audio jack, which is probably why it's hw:0,1. I should also note that I had to fiddle a bit with the channel mapping in the ttable section of the .asoundrc file. YMMV.

At this point, you should be able to run speaker-test -c 6 -D surround51 to test each speaker individually.

Configure VLC

Finally, you need to configure VLC to always use the surround51 ALSA audio device with 6 channel audio. To do this, create / modify the ~/.config/vlc/vlcrc file:

[alsa]
alsa-audio-device=surround51
# 4199 = 5.1 surround
alsa-audio-channels=4199

Then, run vlc on a video file to play it. I'd recommend trying something like this 5.1 surround sound test video.

Additional Resources / Ideas

Hopefully, this helps you enjoy 5.1 surround sound with your favorite movies!

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