Re: iTunes stuttering, and don't shoot me--it might involve Core Audio
Re: iTunes stuttering, and don't shoot me--it might involve Core Audio
- Subject: Re: iTunes stuttering, and don't shoot me--it might involve Core Audio
- From: Pete Gontier <email@hidden>
- Date: Tue, 09 Aug 2005 10:41:04 -0700
Title: Re: iTunes stuttering, and don't shoot me--it might involve Core Audio
In my particular case, doubling the amount of physical RAM in the machine didn’t help even though it looked as if that allowed everything to be resident at all times.
— Pete Gontier <http://www.m-audio.com/>
From: Ethan Funk <email@hidden>
Date: Tue, 9 Aug 2005 10:25:17 -0700
To: CoreAudio API <email@hidden>
Subject: Re: iTunes stuttering, and don't shoot me--it might involve Core Audio
I have had similar problems with an audio application I have been writing. I suspect this is a problem with Virtual Memory paging portions of the audio buffer in and out. I base this on the fact that I have no dropouts on a 300 MHz old blue G4 machine with 1 GB of physical ram, and I get lots of dropouts on a 1.2 GHz mac mini with 256 MB of memory. In all fairness, I have not looked into this all that much yet, so it's a guess at this point.
It does raise a question I have been meaning to ask: Is there some way to hint to the OS that in the near future, a particular page of memory is going to be needed so the VM engine could have it ready in physical ram for the next core-audio render cycle?
Ethan...
On Aug 9, 2005, at 9:45 AM, Pete Gontier wrote:
When a CoreAudio client application offers control over audio buffering, the buffer in question resides within the application, not the system or the driver. (This can be confusing for Windows folk, because ASIO applications offer controls which do tweak the size of the driver buffer.) The problem could be the buffer iTunes allocates for use with CoreAudio, but, like you, I doubt it, and in any case iTunes would have to offer you control over this.
I too have had trouble with iTunes — in my case with a USB 1.1 disk. My library used to be encoded at 320 Kbps and stuttered occasionally even without writing activity (since the disk is entirely dedicated to my iTunes library). However, when I used iTunes to stream the same library on the same disk over the network, I got no such stuttering. This led me to believe the problem had something to do with iTunes file reading. I wrote an AppleScript to downgrade my library to 192 Kbps VBR, which seems to have worked around the stuttering problem at the expense of some audible-to-me encoding artifacts. I wish I had tried 224. Your mileage may vary.
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