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This article covers configuring audio for optimal playback quality in Arch Linux.

Table of contents:
  1. Changing sample rate
  2. Resampling quality
  3. USB DAC’s
  4. Recommended software

Changing sample rate

By default PipeWire sets a global sample rate of 48kHz. If you need to change it (e.g. you own a DAC supporting a higher value) you can do it by editing the line default.clock.rate = 48000 in the configuration file ~/.config/pipewire/pipewire.conf. For example, if you want 192kHz, uncomment and change value 48000 to default.clock.rate = 192000.

PipeWire can also change output sample rates supported by your DAC. To configure, uncomment and set the line default.clock.allowed-rates = [ 48000 ], for example, [ 44100 48000 88200 96000 ]. The sample rate follows the sample rate of the audio stream being played when the card is idle.

To check out which output sample rate and sample format are the data sent to DAC (probably you need to change digits):

cat /proc/asound/card0/pcm0p/sub0/hw_params

To check out which input sample rate is used, change pcm0p to pcm0c (c is short for “capture”, p is for “playback”).

Resampling quality

If you used PulseAudio with resample-method = speex-float-10 or soxr-vhq, then you might consider uncommenting and changing resample.quality = 4 to 10 or the maximum 15 in stream.properties block in both ~/.config/pipewire/client.conf and ~/.config/pipewire/pipewire-pulse.conf (copy them from /usr/share/pipewire/ if they do not exist). Do not forget to restart PipeWire (without sudo): systemctl --user restart pipewire.service pipewire-pulse.socket (never forget pipewire-pulse.socket if you want your config changes to be applied).

There is a very little quality difference between 10 and 15, but the CPU load difference is 2-3x. And the latency difference between 4, 10, 15 is yet to be investigated by anybody. resample.quality = 15 on 44100→48000 Hz on Ryzen 2600 causes pipewire or pipewire-pulse processes to cause 4.0% one CPU core load.

PipeWire uses its own resampling algorithm called Spa. Like with SoX’s sox, Speex’s speexenc, PipeWire includes its standalone version: spa-resample. Usage:

spa-resample -q 15 -f s24 -r 48000 input16bit44100orAnythingElse.wav output24bit48000hz.wav

It is probably somehow possible to use other resamplers by creating your own sink. Or just use a plugin in your music player (e.g., Qmmp has SoX plugin).

TIP: Try to use ALSA output when possible, and avoid unnecessary resampling. Check the current status with pw-top. If the “RATE” column of the default sink matches that of the application outputting audio, pipewire is not resampling the signal.

USB DAC’s

Changing sample rates or formats might help reduce latency with some DACs.

wireplumber (default):

Using matching rules using wireplumber (package) we can set properties for devices.

mkdir -p ~/.config/wireplumber/main.lua.d
cp /usr/share/wireplumber/main.lua.d/50-alsa-config.lua ~/.config/wireplumber/main.lua.d/50-alsa-config.lua

And edit the file accordingly to your needs.

~/.config/wireplumber/main.lua.d/50-alsa-config.lua

--["audio.rate"] = 96000,
--["audio.allowed-rates"] = "32000,96000",

pipewire-media-session:

Using matching rules using pipewire-media-session (package) we can set properties for devices.

Copy the default configuration of alsa-monitor.conf for pipewire-media-session into ~/.config/pipewire/media-session.d. Then append a new rule-block similar to the following one:

~/.config/pipewire/media-session.d/alsa-monitor.conf

rules = {
…
{
matches = [
{
node.name = "alsa_output."
}
]
actions = {
update-props = {
audio.format = "S24_3LE"
audio.rate = 96000
# Following value should be doubled until audio doesn't cut out or other issues stop occurring
api.alsa.period-size = 128
}
}
}
…
}

alsa_output.<name of node> node can be obtained using pw-top.

Your DAC might support a different format or sample rate. You can check what your DAC supports by querying ALSA:

First get the card number of your DAC:

aplay -l

…
card 3: S2 [Schiit Hel 2], device 0: USB Audio [USB Audio]
Subdevices: 0/1
Subdevice #0: subdevice #0
…

So in this example it would be card 3. Get all supported sample rates and formats:

cat /proc/asound/cardX/streamX

…
Playback:
…
Interface 1
Altset 1
Format: S16_LE
Channels: 2
Endpoint: 0x05 (5 OUT) (ASYNC)
Rates: 44100, 48000, 88200, 96000, 176400, 192000, 352800, 384000
Data packet interval: 125 us
Bits: 16
…
Interface 1
Altset 2
Format: S24_3LE
Channels: 2
Endpoint: 0x05 (5 OUT) (ASYNC)
Rates: 44100, 48000, 88200, 96000, 176400, 192000, 352800, 384000
Data packet interval: 125 us
Bits: 24
…
Interface 1
Altset 3
Format: S32_LE
Channels: 2
Endpoint: 0x05 (5 OUT) (ASYNC)
Rates: 44100, 48000, 88200, 96000, 176400, 192000, 352800, 384000
Data packet interval: 125 us
Bits: 32
…
…

In this case S16_LE, S24_3LE, S32_LE are the supported formats and 44100, 48000, 88200, 96000, 176400, 192000, 352800, 384000 are the supported sample rates across all formats.

Recommended software

deadbeef: Modular GTK audio player for GNU/Linux.

yay -S deadbeef

audacious: Lightweight, advanced audio player focused on audio quality.

pacman -Syu audacious

strawberry: A music player aimed at audio enthusiasts and music collectors.

pacman -Syu strawberry

Sources / Further reading:

https://wiki.archlinux.org/title/PipeWire

https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/home

Tags:

Audiophile

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