What is PCM? [SOLVED]

egan · 2010-08-11 19:04:33

What is PCM, and how does it relate to Master, from a volume adjustment standpoint? I never understood what it was, so all my volume handling works on Master only.

I have used oss as my ao in mplayer because I could never get alsa to an audible volume without head phones. Tweaking PCM has no noticeable effect on oss.
Today I sought to find out why alsa was so quiet, and discovered that adjusting PCM works for alsa.

Firstly I want just the knowledge of what it is, and secondly a would like some advice on how it should be used/adjusted for audio playback.

Last edited by egan (2010-08-13 18:13:01)

Anikom15 · 2010-08-11 19:12:35

PCM is what comes from the soundcard, it's the Pulse Code Modulation.

For best results, set all channels to 0 dB gain with alsamixer, and use master or speaker dial to adjust volume.

Other useful channels:
Headphone: usually external speaker
CD: some cd drives have a headphone jack
Line: Line in volume
Phone: Think this is the modem's speaker, not sure
Mic: Mic sensitivity or something, basically the higher, the louder sound from the mic is.

Edit: CD might also refer to data coming directly from a CD, but I'm not sure. You just really need to worry about Master, PCM and Headphone.

Last edited by Anikom15 (2010-08-11 19:15:10)

egan · 2010-08-11 19:52:50

I am actually on a laptop, so I have integrated speakers. The channels I have are Master, PCM, s/PDIF, and s/PDIF Default PCM.

If I understand you correctly, PCM level is the raw level output from the sound card, before it gets to the speakers? As such, what is a good level for PCM?

Last edited by egan (2010-08-11 20:00:57)

heftig · 2010-08-11 20:08:12

No, PCM is for all software audio sources.

Kosmonavt · 2010-08-11 20:11:24

To be completely strict, it's recommended to keep gain in all channels lower than 0 dB. 0 dB - it's not "volume off", but simply a convention. Look, 1 dB = 10 * log( P1/P0 ), where P1 is current power, P0 - some standard power. Usually standard power is the maximum sound volume when card can output without distortion (when sines on output aren't "cut"). So if P1 <= P0, then you get negative or zero dB.

Basically, you should watch PCM and Master channels. From my experience, there's no difference to set one higher than other, just adjust it for your needs. Only thing is that Master channel is easier to align from a volume applet.

Anikom15 · 2010-08-11 20:55:16

0 dB is the best level for PCM.

egan · 2010-08-11 23:04:42

Anikom15 wrote:

0 dB is the best level for PCM.

And why is that?

fukawi2 · 2010-08-11 23:30:10

egan wrote:

Anikom15 wrote:
0 dB is the best level for PCM.
And why is that?

You're letting it through "unaltered" -- no attenuation, and no amplification. It is "clean".

Although in a purely digital environment such as internal to a PC, it's of arguable difference. I guess it's just a 'hold over' from physical analogue mixers that software mixers are emulating.

Arch Linux

#1 2010-08-11 19:04:33

What is PCM? [SOLVED]

#2 2010-08-11 19:12:35

Re: What is PCM? [SOLVED]

#3 2010-08-11 19:52:50

Re: What is PCM? [SOLVED]

#4 2010-08-11 20:08:12

Re: What is PCM? [SOLVED]

#5 2010-08-11 20:11:24

Re: What is PCM? [SOLVED]

#6 2010-08-11 20:55:16

Re: What is PCM? [SOLVED]

#7 2010-08-11 23:04:42

Re: What is PCM? [SOLVED]

#8 2010-08-11 23:30:10

Re: What is PCM? [SOLVED]

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