So you have two problems to solve. The first problem is how to get at
the input data streaming in from the audio device. For that, you can
use an instance of the HAL output unit. You can find a discussion and
sample code for doing this here: http://developer.apple.com/technotes/
tn2002/tn2091.html
Once you have your hands on the data coming in from the device, the
other problem you have to solve is computing the actual meter values
and displaying that on the screen. There are a variety of techniques
for doing metering. Which one you use depends on the effect you are
trying to achieve. They range from the very basic of scanning a
buffer and pulling out the sample with the largest absolute value to
more complex ways of computing signal power over time. A good digital
audio text ought to cover most of the math.
On Jun 18, 2006, at 11:40 PM, Neil Clayton wrote:
Hmm. I may be able to answer some of my own question.
I've looked at the MatrixMixerTest, and I see that it uses the
AUGraph (mixer) plus AudioUnitGetParameter to get hold of avg
power and peak power.
It seems somewhat complex to me (settings up the AUGraph, making
sure formats are correct, etc). I was naively expecting a
'GetPeakPowerFromAudioDeviceID() function'. From my reading so
far, I'm assuming the inputProc is required only to feed data INTO
the mixer (to have something to sample). So my questions are now:
1) For monitoring audio, is using an AUGraph +
AudioUnitGetParameter the preferred way to go?
2) Assuming it is; How would I pipe input from say, a micrphone,
into the mixer? Should I be using AUHAL?
Sorry if these are newbie questions. I'm still very new to
CoreAudio (and audio processing in general).
On 17 Jun 2006, at 13:16, Neil Clayton wrote:
Is there a method I can use in CA to monitor the input level of
some device?
I'd like to do something similar to the input level monitor in
System Preferences / Sound.
--
Jeff Moore
Core Audio
Apple
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