Re: CPU Usage difference
Re: CPU Usage difference
- Subject: Re: CPU Usage difference
- From: Jens Alfke <email@hidden>
- Date: Fri, 6 Mar 2009 15:24:23 -0800
What I found is that, all application who requiere audio output
doesn't have the same CPU usage depending if the audio output is
internal speaker or headphone/line out.
The difference is impressive.
For instance, if we use the Finder to play an audio file :
Line out : CPU charge = 3.5%
Internal speaker : CPU charge = 10.9%
I think Apple ® is doing a software filtering to compensate very
small sized speaker but this difference is really huge.
The speaker and line-out interfaces may be running at different sample
rates. (I've seen this myself; I had a bizarre bug that was triggered
by plugging in headphones. Turned out this reset the HAL to change
between 44k and 48k.) That would mean that sample-rate conversion is
involved in playback over one or the other interface.
If you're curious you could always run 'sample' or Xray on the app
while it's playing, and see where the time goes.
—Jens
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