PULSEAUDIO ARCHLINUX DRIVERS
PULSEAUDIO ARCHLINUX PRO

we need an extra piece of software that manages the output of all applications that needs to use the audio hardware. Whether it's JACK or PulseAudio or esound or dmix etc. Unless you're using a professional audio card, it can't be used by more than a single application at a time. So why is there anything like JACK or PulseAudio? Why do I even need anything 'above' ALSA? IIRC way way back in the day I had to set my volume with alsamixer and IIRC even my Desktop could interact directly with ALSA. Here are some slides (albeit older, though apart from the early stages of pipewire this still holds) from a talk by Paul Davis who is one of the main devs of JACK, on why both are relevant, for a different purpose. Whereas JACK throws that out of the window to provide the quickest response time possible. An obvious example where this comes into play is - for example - power saving, where pulseaudio has facilities where applications which aren't latency critical (like music players) can declare that they can live on a bigger buffer, which will lead to less wakeups as the current state doesn't have to be checked and verified as often.

PULSEAUDIO ARCHLINUX PRO

Wheras pulseaudio is more general purpose focused and JACK is intended for pro audio providing low latencies. To that extent JACK and pulseaudio come in, which are daemons that handle that opening of the sound card dynamically according to the requirements of your currently playing audio. These are however statically configured and in order to change something, you'd have to restart your applications to adjust to a new configuration. To alleviate that, various plugins - the userspace ALSA - have been developed including dmix which mixes everything to a single common configuration and is the one to open the sound card in the end.

That has one big drawback, unless your card itself has a hardware mixer, only one single application can open your card at any given time with their latency and sampling requirements.

PULSEAUDIO ARCHLINUX DRIVERS

I have one more thing to add, which might help clear some of the confusionДЄLSA itself can be split into 2 parts: the actual soundcard driver, and ALSAs userspace plugins, where for example dmix and upmix and all these kinds of ALSA configurations come from.ДЄLSA as-in the kernel driver is the lowest feasible level, this is where all of the other options plug into (which is why JACK is lower latency than 'ALSA' doesn't make sense, yes jack is lower latency than the ALSA userspace, however this is different from the kernel drivers everyone else is dependant from), raw access to this device is provided through the hw:0 and similar identifiers you see in ALSA utilities.

Pulseaudio archlinux