Re: kAudioUnitProperty_Latency and AUPeakLimiter
Re: kAudioUnitProperty_Latency and AUPeakLimiter
- Subject: Re: kAudioUnitProperty_Latency and AUPeakLimiter
- From: William Stewart <email@hidden>
- Date: Wed, 1 Aug 2007 11:30:42 -0700
its a bug (or maybe feature) - the latency for this AU is based on
the value of the kLimiterParam_AttackTime parameter (and it isn't
being updated). This parameter is marked as
"kAudioUnitParameterFlag_NonRealTime"
There are other parameters in Apple's (and others I am sure) AUs that
have similar characteristics. The time pitch is one, parameters on
reverbs and delays will change the "TailTime" and in general it
hasn't been our practise to issue notifications for changes in these
properties based on parameter value changes.
The problem for most host apps is that when the latency changes it
requires some reconfiguration of the rendering engine if you are
going to do anything about it and that will introduce glitches. You
can easily simulate this by running the AUSampleDelay unit in any
rendering engine (AULab will be fine) and changing the amount of
samples it applies a delay too.
You can certainly file a bug, but I'm not sure whether we'd fix it
(and it would in any case remain a problem on Tiger). If you want to
be able to respond to changes like this, then I think a rule of thumb
that you could apply would be that anytime a parameter marked with
this flag (kAudioUnitParameterFlag_NonRealTime) could change Latency
or Tail, so you could reassess at that point. For parameters not
marked with this flag, I don't think you would need to do that work.
Bill
On 01/08/2007, at 8:42 AM, Bjorn Roche wrote:
Hey all,
I am trying to track changes in latency in audio units, so I called
AudioUnitAddPropertyListenerk( audioUnit,
AudioUnitProperty_Latency,
audioUnitPropertyChangedHelper,
this );
Which works for other properties. However, when I test this with
AUPeakLimiter, I never receive events, even though polling reveals
that the property does change value. Is there a bug in my code
somewhere, or is this an apple bug or am I misunderstanding
something? I will resort to polling (after every parameter or
property change, for example), but it seems like there should be a
better way.
thanks,
bjorn
-----------------------------
Bjorn Roche
XO Wave
Digital Audio Production and Post-Production Software
http://www.xowave.com
http://blog.bjornroche.com
http://myspace.com/xowave
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