Re: Coreaudio-api Digest, Vol 5, Issue 76
Re: Coreaudio-api Digest, Vol 5, Issue 76
- Subject: Re: Coreaudio-api Digest, Vol 5, Issue 76
- From: Dominic Feira <email@hidden>
- Date: Tue, 4 Mar 2008 15:32:17 -0500
Daniel,
Logic expects the entire AU render chain to complete in a certain amount of time so it can maintain low latency audio playback. If this doesn't happen it puts up the warning. AU Lab will also warn of overload.
Overloading is not directly related to CPU use. It is all about latency. Overload simply means that the cumulative processing duration for the entire AU chain is too long for at least one render. This can easily happen if you use locks somewhere in your render callback and there is contention for the lock. The render call blocks until it can acquire the lock. By the time this happens too much time may have gone by. In situations like this the CPU use can be very low, but because of lock contention, the latency (the time it takes the AU Render to respond) is too high.
Also, multi-core doesn't really help very much with latency. Core Audio executes its render call on a single thread. In order to utilize multi-cores AU MIDI Instruments and AU Generators would have to do their work on another thread and write their output into a lockless ring buffer. The render can then simply read the audio from the ring buffer which is inherently a very low latency operation. This of course presumes that the instrument in question can render ahead and doesn't have to operate in real-time.
On Mar 4, 2008, at 3:03 PM, Daniel Stenning wrote: I am naturally trying to use Logic8 as my "reference" sequencer when working
on my AudioUnit plugin project but time and time again when attempting to
play logic songs that incorporate my plugin, I end up getting the dreaded
overload messages.
Take a look here just to see the amount of traffic and heat this problem is
generating:
http://discussions.apple.com/thread.jspa?threadID=1322338&tstart=75
Is it not time this was fixed ? OSX is meant to be the "musicians"
OS and Logic8 is made by the same company.
Very often this message crops up when using MIDI AU instruments so there
must be something going on here.
We now have 8 core CPUS and a supposedly multicore friendly leopard OS. Yet
Logic8 still seems to be having problems with songs that are hardly taxing
in terms of complexity. What is going on ?.
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