Everything You Could Ever Need to Know About ALSA - ALSA docs

Everything You Could Ever Need to Know About ALSA - ALSA docs

[Patrick Strasser]

Hello!

Before I get to the point (see next paragraph) I want to say some words 
about ALSA documentation: I can't say more than: I'm confused and 
frustrated. That's incidentally the best description of the current 
documentation. I've looked into the archives, and it was the same state 
about 2 or 3 years before.

I need ALSA, so i need to know ALSA, what it can do, what it can't do, 
and how to get it doing what I want. For now I can't see through all the 
fog of incomplete, not helpful or not existent documentation at all. 
I've dug through the wiki and came to AlsaComplaint page [0].

I've come to the result that I want to understand ALSA and want to share
my knowledge. I want to write the famous but nevertheless not yet 
existing "Everything You Could Ever Need to Know About ALSA"-document.

I need some help for this. I think I'm quite qualified for this task as 
I don't know much about ALSA, so I can ask the right questions. But I 
need people answering my questions.

Let's get into it:

What is this thing about the device?

First the most important question:
I know for now that in a standard configuration "hw:0,0" is quite fine. 
For the second card "hw:1,0" is hopefully working. What exactly does 
that mean?
Sometimes I see "plughw:0,0". What's the difference to "hw:0,0"?
How can I find out which device strings are valid (except for guessing?)

Next: How can I find out which device is the device my speakers are 
connected to?

More will follow...

Patrick

[0] http://alsa.opensrc.org/AlsaComplaint
-- 
Engineers motto: cheap, good, fast: choose any two
Patrick Strasser <patrick dot strasser at  tugraz dot at>
Student of Telematik, Techn. University Graz, Austria



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Re: Everything You Could Ever Need to Know About ALSA - ALSA docs

[Lee Revell]

On Sun, 2006-05-14 at 15:45 +0200, Patrick Strasser wrote:
> What is this thing about the device?
> 
> First the most important question:
> I know for now that in a standard configuration "hw:0,0" is quite
> fine. 
> For the second card "hw:1,0" is hopefully working. What exactly does 
> that mean?
> Sometimes I see "plughw:0,0". What's the difference to "hw:0,0"?
> How can I find out which device strings are valid (except for
> guessing?)
> 

Not quite, you should just use "default" (or "default:0" for the first
card, "default:1" for the second).  Only use hw:x if you know what you
are doing.

Really, you should not have to know this - the app should have a drop
down menu to select the device.

This page explains the varous devices:

http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html

> Next: How can I find out which device is the device my speakers are 
> connected to?
> 

You can't.  Speaker jacks don't normally support this.  You just have to
select the various devices in your app and see which one gives you
sound.  It's no different from any other OS.

Lee



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Re: Everything You Could Ever Need to Know About ALSA - ALSA docs

[Patrick Strasser]

Lee Revell wrote:
> On Sun, 2006-05-14 at 15:45 +0200, Patrick Strasser wrote:
>> What is this thing about the device?
>>
>> First the most important question:
>> I know for now that in a standard configuration "hw:0,0" is quite
>> fine. 
>> For the second card "hw:1,0" is hopefully working. What exactly does 
>> that mean?
>> Sometimes I see "plughw:0,0". What's the difference to "hw:0,0"?
>> How can I find out which device strings are valid (except for
>> guessing?)
> 
> Not quite, you should just use "default" (or "default:0" for the first
> card, "default:1" for the second).

Ok.
I just nowhere found a definition for this :-)

>  Only use hw:x if you know what you
> are doing.

I need something to select my CD sound to record from.

> Really, you should not have to know this - the app should have a drop
> down menu to select the device.

Command lines don't have dropdowns. Aplayer does _not_ give you a list 
with default, default:0, default:1, hw:0,0, hw:0,1 and sensible device 
descriptions for copy-paste.

> This page explains the varous devices:
> 
> http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html

I read this. One primary fact that is missing:
What is a slave?
I don't want a syntactical description, but a semantical. It's used in 
the before mentioned document, but I couldn't find paragraph about slaves.

>> Next: How can I find out which device is the device my speakers are 
>> connected to?
>>
> 
> You can't.  Speaker jacks don't normally support this.  
Of course ;->
> You just have to
> select the various devices in your app and see which one gives you
> sound.  
I thought of some tool that scans through all available channels (left, 
right, center, rear left, rear right, subwoofer, etc.) and pronounce the 
device name and the channel name.  So you would connect your speakers 
like you think it could work and try to get some info about 
device+channel to speaker mapping.

Patrick
-- 
Engineers motto: cheap, good, fast: choose any two
Patrick Strasser <patrick dot strasser at  tugraz dot at>
Student of Telematik, Techn. University Graz, Austria


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Re: Everything You Could Ever Need to Know About ALSA - ALSA docs

[Lee Revell]

On Sun, 2006-05-14 at 23:34 +0200, Patrick Strasser wrote:
> I thought of some tool that scans through all available channels
> (left, 
> right, center, rear left, rear right, subwoofer, etc.) and pronounce
> the 
> device name and the channel name.  So you would connect your speakers 
> like you think it could work and try to get some info about 
> device+channel to speaker mapping.
> 

speaker-test from alsa-utils

Lee



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Re: Everything You Could Ever Need to Know About ALSA - ALSA docs

[Lee Revell]

On Sun, 2006-05-14 at 23:34 +0200, Patrick Strasser wrote:
> >  Only use hw:x if you know what you
> > are doing.
> 
> I need something to select my CD sound to record from.
> 

You can't select to record from the CD with an ALSA PCM device.  You
have to record from default:x (where x is 0 for the first card, 1 for
the second, etc) and set the capture source to "CD" in alsamixer.

Lee



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