CPU spikes - what's the latest?

Question

I posted a question about this in another thread but haven't heard anything back yet - and am desperate for answers so figured I'd try again!
I've just started having a big problem with CPU spikes, seemingly out of the blue.
After having had no problems (that have affected my workflow at least) since updating to Logic 8 when it first came out, the last 2 songs I've worked on have both started having repeated CPU spikes. In both cases the songs (which have for the previous couple of weeks been running fine as I've worked on them) suddenly seem to reach some kind of critical mass and stop at least 4 or 5 times in the song (with a processor overload) making it impossible to mix. The spikes themselves appear to occur every 10 seconds or so.
Though the songs have previously been fine during sections with many tracks, plugins and instruments running, once this starts happening even the most sparse sections can suddenly no longer play without overloading.
In the past, bouncing any instruments to audio or freezing processor-intensive tracks would clearly lessen the load and allow the song to play without a hiccup, but it seems once this starts happening that any attempts I make to pare the song back barely help at all. Even if, in between spikes, the song is running with about 25% max on the CPU meter, when a spike comes both processors momentarily max out and stop the track.
Strangely, with the latest song, even reverting to previous versions (ie from a few days ago when I was having absolutely no problems of this kind) the computer can suddenly no longer cope with the spikes (which I assume have been happening all along but haven't affected playback before now). Weird but true.
I've tried disabling all audio unit plug ins in AU manager, setting all channel strip inputs to no input, running the song using Core Audio rather than the MOTU 828 and repairing permissions with DiskUtility.
Today I tried a clean install of 10.5.3 and 8.0.2 on a new drive (no 3rd party plugins or ANYTHING apart from Logic and OSX installed) - still with exactly the same result.
I've even tried copying all the audio from the arrange into a brand new song, adding the plugins and routing to busses track by track, all the while keeping an eye on the CPU meter. As soon as I've sent just a couple of tracks to aux channels and added only 3 or 4 instances of Channel EQ and Compressor I notice the spiking begin. It's clear that by the time I've finished the setting up of the song the spikes will be maxing out again.
I realise I'm running an old machine (ie Dual 1G G4) but it has, up until now, been working spot on under the current system (I've been using 10.4.11 and hadn't updated to Leopard until today cos I haven't wanted to upset the delicate equilibrium!)
Thankfully I've found a clunky workaround by copying the song on to my Macbook and running that in my studio - a lifesaver but not satisfactory. (I can see the spikes on the Macbook too but playback isn't affected).
I've been using Logic forever and know this behaviour (and unresponsiveness to all my troubleshooting attempts) isn't normal!
I've seen the threads from a few months back but am wondering is anybody else out there still having similar issues? Or has anyone had them and solved them?
Please help!
Cheers
Duane

Answer 1

The latest? It's still spikes constantly here. IMHO, I think there is an issue with-in LP 8 itself with symetric multi-tasking to more than one core... evenly distributing the load between cores. It's hit or miss with me & completely un-predictable and random (the CPU spikes). I've tried all the same quick fixes or work-arounds, of which none seem to make any difference at all. Even setting core audio buffer to 1024 & disabling safety buffer.
Oddly I do find it interesting that on my system anyway, Ivory 1.7 & Atmosphere 1.2, once initially instantiated on an inst track, will consistently evenly distribute between both cores (I have a dual core machine)... and never spike the CPU, no matter how much polyphony I use on either one, with the core audio buffer set to 128. There has to be something the way these two virtual synth plugs are coded differently, to utilize an even symetric threading or distribution to multi cores. -> I am no computer wiz tech head by any means, but this is the best way I can explain it.
Fresh clean install of OSX Leopard 10.5.4 / 2.5GB Ram / LP 8.0.2 / Digi Core Audio 7.4 / Digi 002R