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Re: [Discuss-gnuradio] Sound card configuration

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Sound card configuration
Date: Tue, 9 Nov 2004 10:49:28 -0800
User-agent: Mutt/1.5.6i

On Tue, Nov 09, 2004 at 08:15:21AM -0500, John R. Ackermann N8UR wrote:
> Hi All --
> This may be a little off-topic, but (a) sooner or later I *will* be 
> using GnuRadio with this configuration, and (b) I figure the folks here 
> are quite likely to have been through this exercise.

Not at all off topic.  
I'd rather talk about something besides build problems, anyway ;-)

> I have two sound devices -- the motherboard's VIA8233, which I only 
> intend to use for the occasional song played through the speakers, and 
> an M-Audio Delta44 which is going to be the main workhorse.

> Now both cards seem to be working properly at the physical interface 
> level, but (a) getting both cards working simultaneously is a problem, 
> and (b) I can't figure out how to separate the 4 mono inputs from the 
> Delta44 into either two stereo pairs or 4 separate channels.

Short answer:  Ramakrishnan and I are working on native ALSA support.
All your problems will soon be solved.

Longer answer: ALSA kicks major ass.  Right now I've been working with
both a built-in intel8x0 chip and a Creative Labs Audigy LS.  This is
not an endorsement for this particular card, it was just the cheapest
thing at Fry's that had 6 24-bit channels outbound and 2 24-bit
channels inbound.  I've been able to use it in 2, 4 and 6 channel
output mode and have been able to use the intel8x0 card at the same
time too.

Still a bit of polishing to do on the output side, then the input
needs to be reworked and tested for multiple channels, etc.

Expect a first release by the end of the week.

The i/o model for alsa_sink and alsa_source is this:

The constructor takes a pcm name or a default is provided.  pcm names
look like this: "hw:0,0", "hw:1,0", "plughw:0,0", "surround40",
"surround51", "surround71" etc.  The mapping of all of this stuff to
hardware and software plugins can be controlled though your ALSA
~/.asoundrc configuration file.  ALSA is *extremely* configurable, 
and appears to come with reasonable defaults too.  See

Our code queries the specified pcm and figures out what it will do.
This includes min and max channels, sample rates, number of bits, etc.
We set up the i/o signature of the alsa_sink/source to match the
hardware.  That is, if you specified "surround51" (and your hardware
will do it), we'll give you 6 outputs.  All inputs and outputs to
audio sources and sinks are streams of floats in the range [-1, +1].
This allows your application to stay the same regardless of the
resolution of the underlying hardware.  It's up to you to interpret
the N channels however you like.


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