Re: PCM hw mixing with volume

[Takashi Iwai <tiwai@suse.de>]

At Tue, 09 Mar 2004 09:26:56 -0500,
Paul Davis wrote:
> 
> >And by that time, games will be even more demanding than before, and
> >still want to use those cycles for itself rather than software sound
> >processing, so just sitting idle waiting for the ultimate
> >infinite-megahertz cpu, that can do everything in no time, gains nobody
> >anything... at least our business won't.
> 
> but don't you also want to be able to sell as many copies as possible
> to as many satisfied customers as possible? if so, you have to pay
> attention to whatever standards can be found for the domain at
> hand. in this case, the AC97 codec spec (and its recent successor
> whose name i forget) is about the most relevant thing i can think
> of. AFAIK, AC97 etc. say nothing about the kinds of gain control and
> mix routing that exist for multiple PCM streams. ergo, there is no
> standard way to do this that will work across a significant fraction
> of the installed and/or potential user base.

BTW, the USB audio is another headache.
the current ALSA PCM model isn't perfectly suitable for the devices
like USB audio.  (well, the current JACK implementation has the same
problem, too ;)

just an off-topic here, though...

> so, either ALSA can come up with such a thing, which might be
> interesting but the manpower available to work on it is very limited,
> or parties that have a vested interest in it can use an existing API
> (SDL springs to mind, though i've never looked at it) or develop a new
> one that provides a standard mechanism for doing wat you want.
> 
> i mean, even at the most basic level, the audio interface that is
> built into my laptop motherboard (some intel nonsense) cannot do any
> sample rate other than 48kHz! this is a high end laptop (HP Pavilion
> zd7000, 3GHz processor, 1440x900 display, etc) ... think of the cycles
> that will be spent *resampling* your audio independently of the mixing
> step. this type of BS seems to be growing more and more common. if i
> was in your position (specifically, if i have to assume that my user
> base spent a (comparatively) lot of money on a graphics card, maybe
> even paid for a 5.1 speaker setup, but are still using the
> factory-provided audio interface, i would assume the absolute worst
> capabilities for that interface that i could: single sample rate,
> single PCM stream, no mixer.
> 
> and btw, i wasn't suggesting that you just "sit there waiting". my
> point was that the time you might spend working on this could be spent
> working on something else, and by the time you're done, CPU speed
> increases will have done this particular task for you.

i guess that the special implementation for sb live! would be
relatively easy once when the API is defined.  it's nothing but a
reduced version of PCM streams, so the h/w control is already in the
driver.
the most difficult part is the definition of the (somehow) generic but
effective API.  the same is true for 3D audio API.

it'd be appreciated if app developers have a concrete wish list of API
design about these stuffs, or even better a proposal of the API.


Takashi


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