Re: hardware channel mixing

[Florian Schmidt <mista.tapas@gmx.net>]

On Fri, 3 Sep 2004 10:04:29 -0400 (EDT)
Patrick Dumais <pat@dumaisnet.ca> wrote:

> 
> That's the thing. I'm writing a soft-sampler. meaning that I have
> multiple samples playing at one time when the user presses the keys on
> his midi keyboard. I don't like software mixing because I feel I could
> gain quality by relying on the hardware (am I right?).

No.

> And I also want my app to go
> faster by letting the hardware do this job. But I realize that opening
> 16 devices (16voice polyphony for my app) can be ressource consuming,
> so it's a drawback. I'm not too sure what to do.

Also this will not help you any at all in avoiding latency [btw: what
are you referring to as "go faster"?]. And yes, opening 16 devices is
resource consuming..

> 
> Mixing is a little bit more than adding the samples together, you have
> to do clipping and there is also a method shown on
> http://www.vttoth.com/digimix.htm

That method sounds like it's inappropriate for a soft sampler. Mixing is
adding. period. The user will have to make sure not to bust the headroom
by adjusting the samples gains. A method like in the link is maybe
useful for game sound systems, etc.. but a professional audio app should
avoid such approaches like hell. If you want to make sure you don't
bust the headroom, use a hardlimiter[and process everything in a
datatype that can hold the intermediate result], but i wouldn't want my
sampler to tinker with the dynamics at all if not explicitly requested.

> to make prevent one sound to be higher than the other one when one has
> a silence in it. With that in mind I think I could get a high quality
> sound for my app, but would it be worth all the processing? should I
> still use more than one device instead, assuming that I would include
> but functionalyties for users that don't have a compatible sound card.

flo

P.S.: you should come join the #lad channel on irc.freenode.org. there
we can discuss in RT. I hang around there in the evening [gmt] usually

P.P.S.: If you want to avoid all the alsa pcm troubles i strongly
recommend using jack


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