Meaning of alsamixer controls?

[Bengt T]

My PC has the following equipment:

Card: HDA Intel PCH
Chip: Raeltech ALC887-VD

...and I am trying to understand the the alasmixer controls and how the interact.


Alsamixer has the following Playback controls:

Master Controls what?
Headphone
PCM Output from/to what?
Front Audio channel output? Is this used in 2 ch mode?
Front Mic
Front Mic Boost
Surround Audio channel output? Is this used in 2 ch mode?
Center Audio channel output? Is this used in 2 ch mode?
LFE Audio channel output? Is this used in 2 ch mode?
Line
IEC958 Optical audio 1. Difference to ...2 below?
IEC958 Default PCM Optical audio 2. Difference to ...1 above?
Auto-Mute Mode Can be enabled/disabled. Used for?
Channel Mode Can be 2ch, 4ch or 6 ch.
Rear Mic
Rear Mic Boost

...and the following Capture controls:

Front Mic Boost
Capture Capture of what? Difference to Capture 1 below?
Capture 1 Captore of what? Difference to Capture above?
Digital Capture of what? Optical?
Input Source Can be Line, Front mic, or Rear mic. Selects input to Capture?
Input Source 1 Can be Line, Front mic, or Rear mic. Selects input to Capture1?


Some control I beleive I understand byt the ones with ?-mark are unclear to me.

And where/how comes the output from the CD player?

Can anyone clarify or give hints on where to find the information on the Internet please?

[J G Miller]

On Monday, March 2nd, 2015, at 00:38:11h -0800, Bengt T asked:

> Can anyone clarify or give hints on where to find the
> information on the Internet please?

If you are using the ALSA sound system, kernel modules and userspace
libraries (and that is still the case if one is running PulseAudio
daemon on top of ALSA) then the first place to look for information
is at the web site of the ALSA project --

<http://www.alsa-project.ORG/>

Then look for the particular sound card or kernel module driver on
the page

<http://www.alsa-project.ORG/main/index.php/Matrix:Main>

The list of sound cards which have been activated on your machine can
be checked with

cat /proc/asound/cards

and the kernel ALSA sound modules which have been loaded with

lsmod | grep snd

The page on the ALSA project web site linked to from the above
"is my sound card supported" only usually reveals information about
how to install, how to specify the kernel modules for loading, and
a very rudimentary asound.conf file.

But at the bottom of the page there are some links, one of which is
to the unofficial ALSA Source web site. If the site is up, and
the sound card is a common one, there is usually a page of helpful
comments and user experience with workarounds for problems, eg

<http://alsa.opensrc.org/Hda>

Documentation about controls for this specific sound card can be
found on the ALSA project site at


and in the ALSA kernel module documentation eg
/usr/share/doc/alsa-base/driver/

or online at

<https://www.kernel.ORG/doc/Documentation/sound/alsa/HD-Audio.txt>

> Master Controls what?

This is like the master fader of a sound desk. Even if all the other controls
are turned up, if this is set at 0, then no sound will be heard from any of
the outputs.

In general, it is a good idea to turn down completely your physical loudspeaker
volume control to almost off, then turn master to somewhere around 76% - 84%
and other output controls to the same level (in Alsamixer this is usally just
before or where the red element shows) and then while playing some sound file
to turn up the physical control on the loudspeaker to just the right level.

Beware that if you are running PulseAudio, you have to set the master PulseAudio
control to the level 76% - 84%, and that PulseAudio may of its own accord mess
with the ALSA volume controls and set them to 100% and keep resetting them to
that even if you manually change them in Alsamixer.

> And where/how comes the output from the CD player?

All depends on how the CD player is connected (if at all) to the sound card.

If there is a cable connected from the analog out of the CD player, it will
go to the analog CD input of the sound card. Then one has to adjust the
mixer control usually labeled CD.

If there is a very thin cable with just a two pin plug connected to the
digital SPDIF output of the CD player, then it will be connected to one of
the digital SPDIF inputs of the sound card. Then one has to adjust the
mixer control labeled Digital Input or SPDIF input. It is often also
necessary to set the level on the control marked PCM as well to a sensible
level (76 - 88 %).

If the CD player is not connected to anything, then one has to use a
software CD player which does digital audio extraction viz reads the
tracks on the disc and converts them on the fly to sound "files" (in memory)
and plays them through the ALSA sound system just as a sound file on disc
such as a WAV file via the PCM and Master sound controls.

The Capture controls are always a bit awkward to determine their functionality,
except by trial and error. It is related of course to sound recording
and whether or not the sound on the control being capture or not is mixed
in with the main system sound and passed to the loudspeakers or the software
doing the recording.

So if you connect something up to an input device, it is necessary to activate
the capture functionality in order to hear the sound from that device or have
it recorded by some program. Obviously if you were say recording from an
external CD player connected to a digital input, and you had a microphone
connected, you would not want (stray) sounds recorded as well from the
microphone source unless it was intentional eg karaoke singalong with the music.

Hope that helps to explain some of the mysteries of the sound card controls.

[J G Miller]

On Monday, March 2nd, 2015, at 00:38:11h -0800, Bengt T wrote:

> Capture Capture of what? Difference to Capture 1 below?
> Capture 1 Captore of what? Difference to Capture above?

Yes -- these capture controls are related to the number of Analog to Digital
Converters present on the soundcard.

Although dated and written for another chipset, but the same Intel HDA module,
the page at

<http://orion.lcg.ufrj.br/roma/ALSA.html>

should provide you with a better overview of the different input controls,
and also illustrates the point that when directly playing back or recording
via a control, one has to use the appropriate sample rate, otherwise one must
make use of the ALSA plughw plugin to do the sample rate conversion appropriate
to the input/output device.

[Bengt T]

Many thanks for your advices.
/Bengt