Music Setup

Although PipeWire is designed to simplify audio set up, having a fully working music setup requires some manual configuration of settings. The first stage to setting up a stable music system in Linux is to put the CPU into the correct power management mode.

Most Linux distributions set the CPU to ondemand ("on demand") mode by default, which means that the CPU is constantly throttling itself by reducing the frequency of its cores. This is a nightmare for audio processing, which requires precise timing. Even some games will exhibit stuttering audio when the CPU is in ondemand mode.

I will use the cpupower package to manage the CPU frequency governor. You'll find cpupower in the package repository of most distributions, if it's not already installed on your system. To determine your CPU's current power-saving policy, type

cpupower frequency-info

Most likely, it's in ondemand mode.

For a stable, performant music system, put the CPU into performance mode by typing the following at the command line:

sudo cpupower frequency-set -g performance

Because you'll have to do this on a regular basis, it's a good idea to put that line into a one-line Bash script file. You can use any text editor to do this. Save it under a filename such as cpu_performance.sh, and make it executable by typing the following at the command line:

chmod + x cpu_performance.sh

When you run this script (by typing ./cpu_performance.sh), it will prompt you for your sudo password as it's making changes to the computer's hardware.

You can create another version of this script containing the line

sudo cpupower frequency-set -g ondemand

for returning your CPU back to power-saving mode. There is no need to run your computer in performance mode for general computer tasks; this is particularly true if you are working with a laptop.

It's worth noting that there are GUI tools such as cpupower-gui (Figure 2) [2] that can change the CPU governor mode.

Figure 2: A GUI tool like cpupower-gui can change your CPU's governor mode.

PipeWire for Pro Audio

Professional audio applications include music applications such as Ardour [3] and Qtractor [4] along with audio editors such as Audacity [5] for making podcasts. JACK is the audio system that's designed for professional audio work. It offers much lower latency than PulseAudio, along with better routing options. For these reasons, most music programs directly support JACK. Because PipeWire emulates JACK, all JACK-aware applications and utilities should work as normal, even though they are really being routed through PipeWire.

Given the speed of modern CPUs, you could easily underestimate the amount of CPU power required for audio processing, but each audio sample has to be played back at precisely the right moment, which is why it's so taxing on the CPU. For 48kHz audio, a sample must be played back 48,000 times per second for a mono audio track. Multiple stereo audio streams further add to the CPU workload.

For this reason, the emulated PipeWire JACK environment tends to be shipped with rather conservative settings balanced for general purpose use. The default latency won't be low enough to play instruments in real time from within a music program. The default settings are a 48kHz sample rate and a buffer size of 1,024. If you divide 48 by 1,024, this gives a latency of 21ms, which is a bit slow and results in a noticeable delay.

Setting the Latency

Thankfully, it's not too difficult to set things up for real-time playback within PipeWire. Start by entering the following at the command line:

pw-metadata -n settings 0 clock.force-quantum 256

This sets a buffer size (a "quantum" in PipeWire jargon) of 256, giving a latency of around 5.3ms. This latency is suitable for playing instruments. Test your choice of music program with this setting to see how your computer performs. If your computer can handle this setting, there should be no unacceptable CPU spikes or audio drop outs.

If you are processing audio in real time, you might need an even lower buffer size, and most audio programs will tolerate changing PipeWire's settings while they are running. This gives you the scope to experiment.

For example, if you are playing an electric guitar directly into your audio interface and applying effects to it, you will probably notice a 5.3ms delay between plucking the string and hearing the sound. A buffer size of 128 is a good bet for this type of audio work, and most reasonably up-to-date computer hardware can handle it. It's impossible to calculate precise latencies at this level because there are a few overheads with the computer's hardware and software processing, but this gives a latency of around 2.6ms, which is really low. To put this into context, this is the audio delay that you would experience when standing about one meter away from a speaker. However, you will notice an increase in CPU usage the lower you set the buffer size.