[linux-audio-user] hardware mixing - what it _actually_ is?

Mark Knecht markknecht at gmail.com
Mon Jan 22 19:58:13 EST 2007

On 1/22/07, Paul Winkler <pw_lists at slinkp.com> wrote:
> On Mon, Jan 22, 2007 at 05:29:16PM -0500, Lee Revell wrote:
> > "Hardware mixing" in ALSA terminology refers to the mixing of multiple
> > sound sources from the PC by the hardware.  For example, mplayer
> > output and system notification sounds.
> Yeah. I suspect (and Mark apparently did, too) that the original
> poster meant to ask about hardware monitoring, which is completely
> different :-)
> Explanation here:
> http://ardour.org/manual/recording/monitoring
> That's what the RME and ice1712 cards (among others) support...
> Ardour is the only app I use that has any use for this feature.
> This requires software to control the soundcard's onboard monitor
> mixer. "Normal" ALSA mixers such as alsamixer will not do the job.
> For the ice1712 cards, the app that does this is "envy24control".
> --
> Paul Winkler
> http://www.slinkp.com

Yes, although I was thinking about both. In the case of the original
poster, independent of what he actually asked I suspect that hardware
monitoring is what would make the biggest difference in using a sound
card in a real recording session. I know in my work that has pretty
much always been true.

Hardware mixing, using Lee's definition, isn't all that interesting to
me since multiple ALSA sound sources can be mixed in Jack pretty much
as easily, albeit you probably cannot get as many mixes actually out
to the sound card as you can create in the card itself. None the less,
even if I mix ALSA sources as Lee was suggesting I find that I'm
pretty much always mixing something else in at the card. Is that just
me? I often mix almost everything that's live at the time in at the
card level, including vocals. Vocals come in dry and go out
immediately to a hardware reverb to get a wet mix for headphones. The
dry version goes on to the system to be recorded, whereas the wet
version is what the singer hears. This allows me to use any reverb
setting they are happy with but still preserve the dry vocal for later

I do not really consider the above scenario 'hardware monitoring'
although I can see how others might, since I use the hardware mixer to
insert the vocals into the stream being played by the computer. Zero
latency, happy singers, etc.

One other possibility that occurred to me over my afternoon tea break
was that possibly Lee was making reference to whether the hardware
mixing capabilities are exposed at the system level so that they can
be controlled by ALSA apps. Thomas and I had discussions about this
when hdspmixer was written. For reasons of his own he chose on purpose
not to expose these features to also so as far as I know the only way
to control them is with hdspmixer. This is the same as in Windows to
the best of my knowledge.

Hope this helps,

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