Re: Offline processing
Re: Offline processing
- Subject: Re: Offline processing
- From: Alberto Ricci <email@hidden>
- Date: Tue, 4 Feb 2003 09:12:01 +0100
Forgive my ignorance, but does the AudioUnit standard provide for the
analysis/ pre-pass step that the usual "off-line" plug-ins - such as
normalize - require?
As far as I can tell, it currently doesn't. Doing that implies that
the process becomes non-causal. You would definitely need some
callbacks for retrieving future samples from the host.
Our "Offline" plug-in Pitch 'n Time also makes extensive use of the host
app's "current selection", ie what range of samples is selected. This is
This would be an essential callback among the various ones that would
be required for non-causal processing.
The getter callbacks would be, more or less:
- get the selection range (over time and over channels)
- get the available number of channels
- get the available number of samples (for each channel)
- get a specified number of samples starting at a specified position
In my old SoundEffects and SoundMaker applications, I also provided
some callbacks for dealing with other documents. A plug-in was able
to create a new document and store samples in it, or access an
existing document's samples and read them. I frankly don't think
there is this need with AUs, but please tell me if you think
differently.
One reason why you would want to do that is for outputting samples at
a different sampling rate or sample size (because sampling rate and
sample size are constant within a single document, of course). But
we've got Audio Converters in CoreAudio for doing this.
A simple example is the user's ability to type in the required target
length instead of the expansion ratio. I understand you don't want to
restrict the AU standard to conventional hosts, but a standard way to access
this information when it /is/ available is extremely important.
I agree. When time expanding, you must be able to preview what size
your sound will become.
Alberto.
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