From alsa-devel-owner@alsa.jcu.cz  Fri Feb 26 17:29:45 1999
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Date: Fri, 26 Feb 1999 08:23:59 -0800
To: alsa-devel@alsa.jcu.cz
From: "Kevin Duffey" <kduffey@inprise.com>
Subject: Re: CVS changes
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>As someone else mentioned, it would be nice if this change provided an
>interface for hardware mixing (like 3d sound and SB environmental
>extensions). Also, it would be nice if the mixer could support 4 channel
>and 5.1 channel sound output. And I imagine there are interfaces for
>multichannel input, too, for 3d sound recording. 
>
>I'm not sure all of this falls under the mixer, but what is the current    
>vision for how 3d sound will be played (both low-level and through the   
>library)? There are software algorithms we could use in place of actual 
>3d sound hardware mixing, but we need a nice interface to abstract that
>as much as possible. Also, are there 3d sound stream formats which need
>to be supported?
>
>I've looked into this some, but if there are people knowledgeable on
>this topic, it would be great to make sure we get the proper interfaces
>in place for this.

I am not sure if I am the one who mentioned this..but I know I said
something about how DirectX on the Wintel platform handles hardware mixing
IF a soundcard supports it..otherwise it does software mixing. The same is
true for Direct 3D. If the hardware supports 3D streams, its mixed in
hardware. I dont mean to use the DirectX and MS stuff as an example..but
they do have the right idea. Most soundcards coming out these days have
some way of mixing auido in hardware, usually the 32 voice synth, or some
sort of "streams" mixing. 

Somewhere in the library, maybe at the mixer interface, there needs to be a
pointer that points to the actual audio mixing routine. This way..if the
soundcard supports mixing, the pointer can point to whatever the driver
does to stream the audio channels to the soundcard. If not, the pointer
points to our software mixing routine (hopefully done at the kernel level
in the background). 

Any thoughts?


Kevin Duffey
kduffey@inprise.com

