Jacob Meuser wrote:
On Tue, Dec 22, 2009 at 12:43:02AM +0000, Jacob Meuser wrote:
On Mon, Dec 21, 2009 at 07:46:20AM -0600, Chris Bennett wrote:
Now how do I get these channels out?
I find the mixerctl output for this one, rather confusing
read azalia(4).
you should read the manual, of course. the most important part of the
manual is the part that explains the azalia architecture. this is
important to understand for the mixer item names to make sense, since
the mixer items represent widgets in the codec.
oh, I forgot to explain a basic codec there. I explained all the
parts but never really gave a "big picture".
so here is an explanation of how playback works (should maybe find
it's way into azalia(4)?), with examples using your mixerctl output
(though I removed the "vendor" controls, since they are gone in
-current).
As exlained in the manual, dac widgets convert digital data to
analog sound. In most cases, dacs get data from the host controller
when an application write()s audio data to the device. The dacs
convert the data to sound and that sound travels through the codec,
eventually reaching a jack or some other endpoint widget. The path
of the sound can be determined with the mixer controls that have the
"source" property name.
Output jacks cannot be source widgets, and therefore will always have
a source property control. Also, dacs will always be a source for
some widgets, otherwise there would be no way for the codec to play
analog audio. Quite a bit of information about a codec can be
obtained by looking at the source property widgets that have at least
one dac as a source.
The following command will display source property controls that have
at least one dac as a possible source.
$ mixerctl -v | grep _source=.*dac
The above command produces the following output on a machine with a
Sigmatel codec. Output on other machines, even other machine with the
same codec, likely varies.
outputs.hp_source=dac-0:1 [ dac-0:1 dac-2:3 ]
outputs.mic_source=dac-0:1 [ dac-0:1 dac-2:3 ]
outputs.line-in_source=dac-2:3 [ dac-2:3 ]
outputs.spkr_source=dac-0:1 [ dac-0:1 ]
outputs.SPDIF_source=dig-dac-0:1 [ dig-dac-0:1 adc-0:1 adc-2:3 adc-4:5 ]
As explained in the manual, the channels that the dacs will convert
are encoded in the dac names. dac-0:1 converts channels 0 and 1, also
known as the first stereo pair. In the above output, the hp, mic and
spkr widgets all have dac-0:1 as their source, and so will receive
both channels of stereo playback. The line-in widget is configured
to receive audio from dac-2:3. The line-in widget will therefore
receive the third and fourth channels, and will not receive any sound
unless at least 3 channel data is played.
Note that some jacks can be configured for either input or output.
A jack that is configured for input will not receive any sound
from it's source. As explained in the manual, the mixer controls
with the "dir" property name control the direction of the jacks.
The following command will display the current and possible directions
for jacks whose direction can be changed.
$ mixerctl -v | grep '_dir='
That command produces the following output on the example Sigmatel
codec.
outputs.hp_dir=output [ none output input input-vr0 input-vr50 input-vr80 ]
outputs.mic_dir=input-vr80 [ none output input input-vr0 input-vr50
input-vr80 ]
outputs.line-in_dir=input [ none output input input-vr0 input-vr50
input-vr80 ]
outputs.spkr_dir=output [ none output input input-vr0 input-vr50 input-vr80 ]
In this configuration, only the hp and spkr widgets will receive sound
from their sources.
Thanks, that was very helpful.
The direction part is clear except for the input-vr0, input-vr50,
input-vr80.
For what reason would I pick each of these? Is this used to reduce
excessively loud inputs?
What were or weren't the vendor things?
Do I see this correctly:
I could play 6 channels with mplayer.
0:1 to one output.
2:3 to another
4:5 to adc-4:5 to sp/dif and then decode that stream externally.
This would then give 5.1 output.
This may seem a little weird to do, but older Sony 5.1 receivers that
are "broken" with easy to fix cold solder joints are only about $25 to buy.
--
A human being should be able to change a diaper, plan an invasion,
butcher a hog, conn a ship, design a building, write a sonnet, balance
accounts, build a wall, set a bone, comfort the dying, take orders,
give orders, cooperate, act alone, solve equations, analyze a new
problem, pitch manure, program a computer, cook a tasty meal, fight
efficiently, die gallantly. Specialization is for insects.
-- Robert Heinlein
