Re: Does anyone get an AudioDevice that has both input and output channels? (question is related to software play through)
Re: Does anyone get an AudioDevice that has both input and output channels? (question is related to software play through)
- Subject: Re: Does anyone get an AudioDevice that has both input and output channels? (question is related to software play through)
- From: Laurent Cerveau <email@hidden>
- Date: Wed, 18 Jul 2001 23:01:01 -0700
On Wednesday, July 18, 2001, at 09:06 PM, James McCartney wrote:
>
At a cost of how much additional CPU overhead compared to 128 or 256 ?
>
The purpose of OS X audio architecture is to provide to you, as
application developer,
the choice in the latency needed for your app. As every dsp system,
there are decision
to take about where you want to use CPU. The plain thing here is : if
you want or need
(very very ) low latency you can get it.
>
If these smaller buffer sizes are not suitable for a certain situation,
>
then
>
added latency may not be desirable. For example with FFTs where you
>
need to
>
do a whole buffer at once, you cannot reduce the latency below the FFT
>
buffer size, and adding an additional buffer of latency the size of the
>
FFT
>
may not be desirable.
Again what is the purpose of your fft? If the purpose is to have
spectrum displayed you
may not prefere to do your fft directly in you app IOProce but pass the
samples to another
thread where you do the hard work. Then you can have also better
frequency resolution,
as you have more point into you FFT (damn god ! time-frequency
compromise again!!!).!
As for the built-in hardware : having it presented as two devices or one
change nothing.
It is just a convenience in term of application developer, and it makes
more sense as the
2 hardware DMA engines on the mac IO controller are driven by the same
clock, and
won't drift (so this is a good candidate for presenting synchronized
IO). We are plenty
aware of that. But that won't make the samples come and go faster (or
slower) into
the machine, or to/from the HAL :-).
Regards
Laurent
--------------------
Laurent Cerveau
AudioCPU SW - Manager
Apple Computer Inc.
email@hidden