Re: Live mixing; how does CA do it smoothly?

• Subject: Re: Live mixing; how does CA do it smoothly?
• From: Bill Stewart <email@hidden>
• Date: Mon, 9 Dec 2002 17:51:46 -0800

On 07.12.2002 at 6:19 pm -0500, Kurt Revis wrote:

The HAL mixing happens below the level of your application, so I don't
think there's any way you can directly get that data. If libsndfile
expects samples <= 1.0, that's what you should give it.

BTW, if you are using an output audio unit, you can see the audio data
after it is played by using AudioUnitSetRenderNotification(). (Look for
kAudioUnitRenderAction_PostRender in the AudioUnitRenderActionFlags
passed to your callback.) I believe this will take into account the
output audio unit's volume.

Thanks for the suggestions Kurt.

It occurs to me that I might be able to mitigate the clipping problem by
inserting a PeakLimiter AU in the chain. A (very quick) play with one of
the AU demo apps shows it's got paramaters for attack/release/etc so it
might be a good automated solution.

There then lies the problem of getting output from the peak limiter.
Using render notifications would work during live playback, but not
suitable if I want to mixdown to disk without playing back in real-time.
From reading the list it seems like using a Generic Output unit is the
ticket in this case. So my next question: is the generic output also
available under 10.1?

AUNTComponent.h implies there is a V1 unit at least under Jaguar, which I
infer (being V1) is also available under 10.1. However, in a May 18th
message to this list Bill Stewart said "...this is a new audio unit
(Generic Output) that is available in Jaguar..." which implies this isn't
the case.

(If there isn't any generic output under 10.1, what can I do? Can I just
pull AudioUnitRenderSlice() on the peak limiter, or do I NEED to have an
output unit?)

-ben


-- Ben Kennedy, chief magician
zygoat creative technical services
613-228-3392 | 1-866-466-4628
http://www.zygoat.ca
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