How to use softvol to control the master volume

How
to use softvol to control the master volume

This howto describes a workaround if your master volume doesn't work. This happens if your sound card can't control the volume on the hardware side or the driver doesn't support
this feature of your sound card. Maybe updating ALSA or using another module will fix the problem. If nothing works, you can define a new virtual pcm device in the .asoundrc file,
which controls the volume on the software side.
Once you followed this howto, please leave a small feedback on the discussion
page.

Preparations

Find out on which existing PCM device you can base your setup. In this device, the audio data will be processed the last on its way to the sound card. In a simple stereo setup,
this is problably just the

hw:0,0

device.
If your card doesn't support hardware mixing, you may have to use a

dmix

plugin
first (see example
below). In a typical 5.1 surround sound setup, you are probably using the predefined

surround51

device.
To get a list of possible devices, you may use:

aplay -L

To test this device, use:

speaker-test -D<device name> -c<channel count> -twav

If that command produces sound on the correct channels and you can use it on two different consoles simultaneously, you can use this device. If simultaneous usage doesn't work,
see dmix and Hardware
mixing, software mixing to enable software mixing.

Editing the asoundrc file

Creating a new softvol device

Open the asoundrc file in your favorite editor. E.g. like this:

nano ~/.asoundrc

Now we create a new softvol device
be typing:

pcm.softvol {
type            softvol
slave {
pcm         "<device name>"
}
control {
name        "<control name>"
card        0
}
}

This will create a new PCM device called

softvol

, which is controlled by a volume control

<control
name>

and which will pass the sound data with the changed volume to its slave

<device name>

.
You have to replace

<device name>

with the name of the device you determined above and

<control
name>

with what you want to call your new volume control, e.g.

SoftMaster

. If your card does not have a master volume control at all, you're lucky, because you can name
your new volume control

Master

and your new control works like a master volume control is supposed to. To find out, whether such a control exists, run:

amixer controls | grep Master

If this command lists a control named

Master

, you should not name your new control like this. Unfortunately,
existing controls can't be overwritten, so you have to pick a name like

SoftMaster

. This control will now control everything, but as it is not called

Master

,
mixers (like KMix)
won't use it to control master volume, unless you can make them choose another control (likeGMix).
Now test your new device with:

speaker-test -Dsoftvol -c<channel count> -twav

Note: The new volume control won't appear immediately! Only after the first usage of the newly defined device (e.g. with the command above), should

amixer
controls | grep <control name>

display your new control. Mixers that were already started before the first usage (like KMix) have to be restarted to adopt the changes. If you still don't see the new control, try restarting ALSA or your
PC.

Make applications use it

Finally, we'll have to make all applications use this new device. In a simple stereo setup, we can redefine the default device and route it to our

softvol

device
(with a

plug

device, so rate is converted automatically). In that case, add this to your asoundrc file:

pcm.!default {
type             plug
slave.pcm       "softvol"
}

If you have a multi channel sound card, you may want to upmix these stereo signals first (see SurroundSound).
It is useful to redefine the

surround40

,

surround51

... devices in the same way, so everything is passed through our new
softvol device by default. Note that you should not overwrite the device

<device name>

from above!
Make sure that every application uses a device that is redirected to your softvol device because everything else will not be controlled and may be too loud! If you can't redefine
the default devices, you have to configure your applications separately.
Note, if your

<device name>

happened to be named "default" literally, you will
have to go back to the first step, and use "cards.pcm.default" instead of just "default" in pcm.softvol slave pcm block. Otherwise, when trying to replace default output, you will get error

ALSA lib conf.c:4049:(snd1_config_check_hop) Too many definition levels (looped?)
Playback open error: -22,Invalid argument

Common example with dmix

In the latest ALSA versions
(after 1.0.9) dmix has been enabled by default for the boards that need it, so in order to benefit for both features
(softvol+dmix) you must have in ~/.asoundrc something like this:

pcm.!default {
type            plug
slave.pcm       "softvol"   #make use of softvol
}

pcm.softvol {
type            softvol
slave {
pcm         "dmix"      #redirect the output to dmix (instead of "hw:0,0")
}
control {
name        "PCM"       #override the PCM slider to set the softvol volume level globally
card        0
}
}

In this case, the device called

dmix

is the device

<device
name>

the whole setup is based on (see above).
This works for my crappy C-Media Electronics CMI 9739 - nforce2 integrated 'soundcard' that lacks both volume control and mixing in hardware. I think it will do for many other
similar 'soundcards'.

More complex example

I am using an SBLive! Platinum [CT4760P] and the asoundrc file
below. Maybe you can solve your problems by understanding this example and maybe copy parts of it.
On the lowest level, I have two

softvol

devices that pass their data to the predefined devices

front

and

rear

controlling
their volume with the controls

Front Master

and

Rear Master

. A

multi

plugin
merges those two stereo devices into a four channel device. My

multi

device would be the

<device name>

device
in the text above. The device called

softvol

controls the volume with a control called

SoftMaster

using
the

multi

device as slave. I then define an upmix device to upmix stereo streams to 4.0 and some downmix devices to downmix 4.1, 5.0, 5.1 and 7.1 streams to 4.0.
To enable recording with multiple applications, I define some

dsnoop

devices.

dsnoop

does
the same thing with recording as

dmix

does with playback. The device

recording

is
a regular stereo recording device, whereas

recleft

and

recright

are mono devices recording only
one channel of the stereo stream. If you want to plug two mono mics into the stereo mic plug of your sound card (with an adapter) and record from them separately, this is quite handy, otherwise, this part is not necessary.
Finally I replace the

default

device with a

asym

device,
redirecting its playback to the upmixing device and its recording to the recording device. This way, the

default

device is playback and recording device at the same time (full
duplex). I also create the

surroundX

devices redirecting to the corresponding downmix devices.
What I didn't consider yet in my file are devices needed for compatibility with OSS and
similar. If I need them one day and change my config file locally, I'll post an update here.

#-------------------------------
#  Volume
#-------------------------------

# volume of all channels
pcm.softvol {
type        softvol
slave.pcm   "multi"
control {
name    "SoftMaster"
card    0
}
}

# splitting the channels in front and rear
pcm.multi {
type    multi
slaves {
a.pcm        "frontvol"
a.channels   2
b.pcm        "rearvol"
b.channels   2
}
bindings {
0.slave      a
0.channel    0
1.slave      a
1.channel    1
2.slave      b
2.channel    0
3.slave      b
3.channel    1
}
}

# front
pcm.rearvol {
type        softvol
slave.pcm   "rear"
control {
name    "Rear Master"
card    0
}
}

# rear
pcm.frontvol {
type        softvol
slave.pcm   "front"
control {
name    "Front Master"
card    0
}
}

#-------------------------------
#  Recording
#-------------------------------

pcm.recording {
type        dsnoop
ipc_key     2589
slave {
pcm     "hw:0,0"
format  "S16_LE"
}
}

pcm.recleft {
type        dsnoop
ipc_key     2589
slave {
pcm     "hw:0,0"
format  "S16_LE"
}
bindings.0 0
}

pcm.recright {
type        dsnoop
ipc_key     2589
slave {
pcm     "hw:0,0"
format  "S16_LE"
}
bindings.0 1
}

#-------------------------------
#  Upmix
#-------------------------------

# upmix stereo to 40
pcm.upmix {
type        route
slave.pcm   "softvol"
slave.channels    4
ttable {
0.0    1
0.2    1
1.1    1
1.3    1
}
}

#-------------------------------
#  Downmix
#-------------------------------

pcm.downmix41 {
type        route
slave.pcm   "softvol"
slave.channels    4
ttable {
0.0    1
1.1    1
2.2    1
3.3    1
}
}

pcm.downmix51 {
type        route
slave.pcm   "softvol"
slave.channels    4
ttable {
0.0    0.67
1.1    0.67
2.2    1
3.3    1
4.0    0.33
4.1    0.33
}
}

pcm.downmix71 {
type        route
slave.pcm    "softvol"
slave.channels    4
ttable {
0.0    0.34
1.1    0.34
2.2    0.67
3.3    0.67
4.0    0.33
4.1    0.33
6.0    0.33
6.2    0.33
7.1    0.33
7.3    0.33
}
}

#-------------------------------
#  Overwrite existing devices
#-------------------------------

pcm.!default {
type           asym
playback.pcm   "plug:upmix"
capture.pcm    "plug:recording"
}

pcm.!surround40 {
type         plug
slave.pcm    "softvol"
}

pcm.!surround41 {
type         plug
slave.pcm    "downmix41"
}

pcm.!surround50 {
type         plug
slave.pcm    "downmix51"
}

pcm.!surround51 {
type        plug
slave.pcm    "downmix51"
}

pcm.!surround71 {
type         plug
slave.pcm    "downmix71"
}