Re: Problem with AUParameterSet

Subject: Re: Problem with AUParameterSet
From: William Stewart <email@hidden>
Date: Wed, 21 Feb 2007 19:23:09 -0800

I don't follow you.

What you describe is basically what AUParameterSet does. I'm concerned about doing VU Meters this way - it seems to me from your description that you would be changing the parameter value in your render call - if that ends up sending a notification each render call that is alot of notifications. VU Meters are better done by marking the parameter as a VU meter and then having the view poll for its value a few times a second to draw it (this is how we do the meters in the compressor/limiter AUs)

Finally, I'm also confused about your comments about stopping the time line and showing problems in AULab - AULab does have a transport, but it doesn't have a timeline and has no notion of feeding silence to an AU. I'd be happy to look at this if you can see a problem in AULab and we can reproduce it here.

HTH

Bill

On 20/02/2007, at 9:17 AM, Eric Johnson wrote:

Hi Bill,
We found a slight modification to our original code that works. We call AudioUnitSetParameter followed by AUParameterListenerNotify instead of just calling AUParameterSet and the problem goes away.

In an earlier thread (Wed, 19 Jul 2006) on the CoreAudio list, you stated,

AUParameterSet is not an AU API - rather it is an <AudioToolbox/ AudioUnitUtilities.h> API (AudioEvent...) - it does 2 things:
- calls AudioUnitSetParameter
- calls AUEventNotify

So, what is the difference between AUEventNotify and AUParameterListenerNotify?

More info about how we're using these calls:
Our ProcessBufferLists method is called via AUEffectBase::Render. Our Audio Unit process component processes its inputs and thus modifies the parameters that the VU meters are "listening" to. The problem occurs when using some hosts (Peak, AU Lab) when the transport is paused. ProcessBufferLists continues to be called with buffers of zeros as inputs. AUParameterSet gets called, but the listeners aren't notified. Once playback resumes, AUParameterSet starts notifying listeners again.

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References:
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	>Re: Problem with AUParameterSet (From: William Stewart <email@hidden>)
	>Re: Problem with AUParameterSet (From: Eric Johnson <email@hidden>)
	>Re: Problem with AUParameterSet (From: William Stewart <email@hidden>)
	>Re: Problem with AUParameterSet (From: Eric Johnson <email@hidden>)

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