Re: best performing mixer solution
Re: best performing mixer solution
- Subject: Re: best performing mixer solution
- From: William Stewart <email@hidden>
- Date: Mon, 9 Oct 2006 17:33:02 -0700
The 3DMixer contains a cheap rate converter feature on its input. Its
the only mixer AU that we ship that does - all of the others require
the sample rates to match.
Bill
On 09/10/2006, at 4:47 PM, John Morris wrote:
I am trying to set up some simple audio playing. My needs are very
simple, play multiple channels of sound (of various sample rates)
and be able to adjust their volumes on the fly. I have an AUGraph
with a default output (kAudioUnitSubType_DefaultOutput) and a
stereo mixer (kAudioUnitSubType_StereoMixer) on top of that. I
then just render the sounds directly into the various elements of
the mixer and control it's volume there (in the mixer).
I already have a system that performs well except for one gotcha.
Everything is fine when I play 44.1kHz samples, but when I go to
22kHz, it is playing too fast (like the rate is still 44.1kHz).
When I go to play a sound, I check the rate of the mixer element,
and if it is different from the sound I want to play, I use
AudioUnitSetProperty(...kAudioUnitProperty_SampleRate,
kAudioUnitScope_Input...) on the proper mixer element. I can check
it afterward, and it is set correctly, but it doesn't seem to have
any effect.
As a test, I switched the mixer to kAudioUnitSubType_3DMixer, and
it is properly handling the 22kHz samples. No other source changes
except for specifying the 3d mixer instead of the stereo one. So,
I would guess that my code is at least mostly working.
So, after all that setup, here comes my question(s).
Am I doing something wrong (or not doing something right) on
changing the sample rate of the stereo mixer?
Do I need to put an kAudioUnitSubType_AUConverter on top of each
stereo mixer element and use that to convert/interpolate the sample
rate? How much of a performance impact would this potentially be?
Should I just use the kAudioUnitSubType_3DMixer? I would assume
that the performance of the 3D mixer would be a lot lower than the
stereo one due to all of the sound localization goodies (that I
would never use). Or would it "do the right thing" and make an
optimal path based on settings that never change?
BTW, I am currently using 10.4.8 (everything up to date) on a
MacBook Pro.
Thanks for any help on this,
John Morris
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