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Well, this confuses me for a long time. As far as I know, ALSA is a package of many sound card drivers, and PulseAudio is a audio application that operate the sound data like mixing or equalizer.

But why there is a control bar called PCM in the panel of alsamixer. Does that actually change volume by controlling the chip on the sound card? If not, why it isn't PulseAudio'a job?

What is the relation between ALSA and PulseAudio sound architecture?

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PulseAudio basically sits atop ALSA, and use it internally. ALSA is unable by itself to be used by multiple applications, so PulseAudio provides this functionality among others.

Summarized:

  • ALSA - dealing with the hardware, basically owning it
  • PulseAudio - a software proxy providing additional featues (mixing, equalizer) between your application and the ALSA/OSS subsystem

This diagram is from the Wikipedia page of PulseAudio:

PulseAudio operational flow chart

  • Could you be so kind and write, where does the ALSA loopback device sits in this model? (the one, that gets installed by sudo modprobe snd-aloop)? – Adam Ryczkowski Mar 21 '17 at 9:43
  • My guess is that is in the ALSA/OSS HW driver square. AFAIK it is basically a soundcard implemented fully in software. – meskobalazs Mar 21 '17 at 9:54

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