Sound: What's the difference between Master, Front, PCM and Capture?

blackhole · 2009-03-02 10:23:02

Hi guys,

like so many others I've been fiddling with my (low) sound levels for snd-intel-hda. In the end my sound was ok. The sound level is not as high as under Windows, but good enough for watching movies.

However I'm always interested in the technical details. Can someone kindly explain to me the difference of those 4 channels: Master, Front, PCM, Capture.
Is that something related to the software meaning the driver or are these channels actually "hardware components" on my sound chip?

Why doesn't my sound chip have a Front channel for example?

In one thread (http://bbs.archlinux.org/viewtopic.php?id=5025) someone said, it would increase the sound level if you increased the Capture channel. So far I assumed the word "capture" would imply something about the microphone. That's input, so why would it increase the output?

Thanks a lot for satisfying my thirst for ever more Linux knowledge,
Blackhole

Last edited by blackhole (2009-03-02 10:24:09)

R00KIE · 2009-03-02 12:27:58

As I see it, it goes like this:
Master: controls the general volume, that is, what gets out after mixing everything (you have pcm sources and midi sources as far as I know)
Front: controls the volume of the front channel. Typically this is needed in multichannel setups (if you have a HDAudio codec and controller with only the front channel connected I guess you will get this too)
PCM: controls the general volume of pcm sources (midi sources have or could / should have a volume control of their own)
Capture: this one can be a tad tricky to explain/understand. You know you have a capture volume that will control the gain of the capture source (usually a microphone but can be line in or cd or any other input source) (this is the recording part). Then you can also output to your speakers what you are recording at the moment, here you have a volume control too and thats called capture, its a playback control like pcm or master (usually you have the capture channel muted so it doesn't bother you).

I hope I'm not saying something wrong and that this makes it a bit more clear to you

simongmzlj · 2009-03-04 00:12:49

Sound on your computer is represted digitally. Speakers, however, need an analog signal. So digital sound has to first go through the PCM. PCM stands for pulse-code modulation. Its a type of digitial to analog converter. Essentially it's what turns a digital sound into an analog one that your speakers can output. This knob changes input gain (explained below).

Now the rest makes sense if you think of a mixing board with multiple inputs and outputs.

Master controls master volume.
Front would be an output channel. (It's simply named something instead of Output 1). You can have more of these depending your soundcard. Lets you adjust the gain on the channel itself.
Capture represents input signal gain. (From a microphone or line-in, it depents on your Input Source settings.) Good thing to look at if your mic is too quiet when on skype or recording music, etc.
PCM is technically like Capture as its an input into the mixing board (from a digital source), and changing the PCM level changes that channel's gain.

blackhole · 2009-03-04 00:55:00

Thanks a lot guys. That helped a lot.

Arch Linux

#1 2009-03-02 10:23:02

Sound: What's the difference between Master, Front, PCM and Capture?

#2 2009-03-02 12:27:58

Re: Sound: What's the difference between Master, Front, PCM and Capture?

#3 2009-03-04 00:12:49

Re: Sound: What's the difference between Master, Front, PCM and Capture?

#4 2009-03-04 00:55:00

Re: Sound: What's the difference between Master, Front, PCM and Capture?

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