Re: Multi Channel Mixer Unit with large number of channels
Re: Multi Channel Mixer Unit with large number of channels
- Subject: Re: Multi Channel Mixer Unit with large number of channels
- From: Brian Willoughby <email@hidden>
- Date: Sat, 30 Oct 2010 14:05:31 -0700
On Oct 30, 2010, at 05:52, Bruno Berisso wrote:
I'm writing a test program that must play 'n' signals (about 600)
at the same time.
In my first try I use the "number of channels in the output unit =
n" but it's distorts the sound or even no play any sound.
Now I try using the kAudioUnitSubType_MultiChannelMixer and
following the same logic ( "number of channels in the output unit =
n") the results are the same.
I was thinking in connect the necessary number of multi channel
mixers unit in cascade to achieve the number of signals I must
process, but i really don't know if it's good idea...
What is the approach in this kind of situations?
You should not need any more than one mixer. I believe that your
problem is amplitude. You have to adjust the input and output volume
of the mixer, or else 600 signals will be at least 300 to 600 times
too loud, resulting in distortion. Mixers do not automatically
adjust volume. The only way to automatically adjust volume is with a
limiter, such as Apple's AUPeakLimiter.
You can try the limiter, but you might not like the fact that you
won't have constant volume. Also, I'm not sure that AUPeakLimiter
can apply the 55 dB of gain reduction that you need for 600 mixed
signals, but you might start with -40 dB pre-gain and hope that the
20 dB of limiting amount is enough after that.
Then again, you might be better off just setting a fixed gain of -56
dB on your mixer output and be done with it. CoreAudio's floating
point format makes this easy to handle in a simple way.
This is all basic audio mixing technique, something you would need to
handle yourself even in an analog mixing studio; it's not an issue
that's specific to CoreAudio.
Brian Willoughby
Sound Consulting
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