Linux Audio Essentials

This post is also in the form of a video blog. Watch the video first!

• Youtube: https://youtu.be/HxEXMHcwtlI
• Peertube: https://peertube.tonytascioglu.com/videos/watch/4a6b4e74-a5af-4616-96f4-5d9773033152

The description below is longer then the one on YouTube, which passed the maximum 5000 character limit. The version here has all the full URLs and any extra comments I might add.

In this video, I explain how audio and sound works on Linux based comptuers and systems. More specifically, I go over the point of sound hardware, kernel drivers such as OSS and ALSA and userspace sound servers such as PulseAudio, Jack and Pipewire.

Along the way, I discuss the advantages and drawbacks of the current implementations, as well as why one implementation is often favored over another. Finally, I discuss the latest-and-greatest sound server, Pipewire, what it means, and how you can benefit from the improvements.

This video is a bit rambly at times, so please stick with me, and I hope you learn something throughout and feed your curiosity. Please feel free to use the timestamps below to skip between sections!

(grouped by topics)

• 00:00 - Introduction

• 00:18 - Basic Hardware, Inputs and Outputs
• 00:36 - Sound Cards (and what they do)
• 01:01 - Digital Audio, PCM and extra hardware

• 01:29 - Kernel Drivers! (How to interact with hardware)
• 01:53 - OSS (Open Sound System)
• 02:12 - ALSA (Advanced Linux Sound Architecture)
• 02:46 - ALSA Limitations - hardware mixing/multiplexing

• 03:54 - Pulseaudio (and sound servers)
• 04:25 - Benefits of PA - mixing and resampling
• 07:26 - Drawbacks of PA (and JACK introduction)
• 08:13 - JACK and its benefits
• 09:57 - Comparison with PA and other software

• 11:12 - Pipewire (and its benefits)
• 14:05 - Future of Pipewire
• 15:17 - Note on Bluetooth (rant)

- note: mostly fixed!

• 17:52 - Conclusion

• https://en.wikipedia.org/wiki/Sound_card

• https://www.alsa-project.org/wiki/Matrix:Main

• https://www.ramelectronics.net/analog-digital.aspx
• https://en.wikipedia.org/wiki/Digital-to-analog_converter

• I didn't get to it in this video, but it explains why 44.1 and 48 kHz are perfectly fine.
• More specifically, how we can perfectly reconstruct analog waves provided no aliasing and they are below the nyquist frequency.
• https://www.allaboutcircuits.com/technical-articles/nyquist-shannon-theorem-understanding-sampled-systems/

• I found these super helpful to understand digital audio and video fundamentals.
• Discusses PCM and more, and also the nyquist stuff from above in video 2.
• https://www.xiph.org/video/
• https://wiki.xiph.org/A_Digital_Media_Primer_For_Geeks_%28episode_1%29
• https://wiki.xiph.org/Digital_Show_and_Tell/Episode_02

• Also see Chris' blog while you're at it, some interesting reads:
• https://xiphmont.dreamwidth.org/

• I found this a simple overview when researching
• https://events19.linuxfoundation.org/wp-content/uploads/2017/12/Introduction-to-Linux-Kernel-Driver-Programming-Michael-Opdenacker-Bootlin-.pdf

• https://en.wikipedia.org/wiki/Open_Sound_System
• https://wiki.archlinux.org/title/Open_Sound_System

• ie: OSS wasn't bad, and had some afvantages over ALSA, but the licensing switch just prompted people to switch
• https://en.wikipedia.org/wiki/Open_Sound_System#Free,_proprietary,_free

https://www.alsa-project.org/wiki/Main_Page

• The sound card compatibility list is above. The Gentoo and Arch wiki entries are useful.
• https://wiki.archlinux.org/title/Advanced_Linux_Sound_Architecture
• https://wiki.gentoo.org/wiki/ALSA

• https://en.wikipedia.org/wiki/Sound_card_mixer
• https://newbedev.com/why-do-you-need-pulseaudio

• Use a sound server. Don't do this manually https://electronics.stackexchange.com/questions/57476/how-do-i-multiplex-many-signals-into-my-sound-card

• Homepage: https://www.freedesktop.org/wiki/Software/PulseAudio/
• User docs: https://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/User
• Git: https://gitlab.freedesktop.org/pulseaudio/pulseaudio

• As usual, the arch page and examples are good:
• https://wiki.archlinux.org/title/PulseAudio
• https://wiki.archlinux.org/title/PulseAudio/Examples

• Homepage: https://jackaudio.org/
• Jack1 git: https://github.com/jackaudio/jack1
• Jack2 git: https://github.com/jackaudio/jack2
• Wiki (and tools using Jack) https://github.com/jackaudio/jackaudio.github.com/wiki
• Archwiki: https://wiki.archlinux.org/title/JACK_Audio_Connection_Kit

• Hoempage: https://pipewire.org/#about
• Neat demo and features, and other benefits discussed on hackaday here: https://hackaday.com/2021/06/23/pipewire-the-newest-audio-kid-on-the-linux-block/
• Archwiki as always: https://wiki.archlinux.org/title/PipeWire
• Wiki - contains useful config parameters for pulse and jack: https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/home
• Git: https://gitlab.freedesktop.org/pipewire/pipewire

• If you have one, your best bet is http://www.ffado.org/

• 0040 - When I say sound card, most computers have one build in these days, eg: onboard audio. Physical discrete cards are mostly a thing of the past.
• 0250 - Sound card multiplexing also often called hardware mixing.
• 1240 - There is also a “Pro Audio” mode for sound cards that splits all the channels
• 1705 - Most of these disconnection issues are now fixed as of the time of publishing!

• I'll add more notes as I remember when rewatching this.

• Please note that due to classes and school and coop, the filming/editing/uploads of my videos are very delayed, and might not be the most sensitive. This video was filmed April 2021, Edited June-July 2021, Description written August 2021. I hate writing descriptions and thumbnails…

Watch this video on Peertube: https://peertube.tonytascioglu.com More info is probably on my wiki: https://wiki.tonytascioglu.com

Copyright 2021 - Tony Tascioglu I'm making this freely available under a CC-BY-SA-NC.

Email: tonytash@pm.me (not monitored 24/7) I might not get to comments on this video until the end of my next school/work term, feel free to post anyways.

I hope you enjoyed the video and learned something!

Randy MacLeod (and the rest of the Wind River Linux userspace team). I know you had asked me about Pipewire at some point, and I already had this video in the works, so hopefully you find it useful :)

• I'll update this as corrections are pointed out.