I am running into CPU overload difficulties with my projects in Reaper. I have tried to be as efficient as possible with running vst's.. for example the four rhythm guitars are routed to a single bus (each with their own eq) so I am only running one instance of my amp sims, compressors, saturators etc for all four guitars.

I then have another track with a bass guitar vst and a drum bus running the Steven Slate sampler (along with individual compressors and eq's on the various tracks within that bus.

I have been monitoring my CPU usage during playback and the max I have seen it hit is 60%... so why then am I hearing lots of crackle as if my CPU is overloading? Is there another cause for the terrible crackling and lag which I am experiencing?

Turning my effects and vst's off get rid of the crackle. Can anybody help? Is my CPU simply not coping even at 60% capacity? (Average during playback in this project it sits around 40%)

What are your system specs?

I get the same thing (I have a fairly modest dual core audio machine, but have been battling processor power since 486's were state-of-the art ? ). The CPU meter doesn't tell you much (in fact, I find it next to useless) - it doesn't give you any idea of memory, disk, bus or interface bottlenecks, which are just as likely to be the source of problems. There can also be momentary spikes that the relatively low sample rate of the meter can't catch. This is where your relatively unsung components like your motherboard and specific chipsets make a huge difference to performance.

I presume you have followed guidelines for optimising your PC for audio? Otherwise, the easiest solution is to raise your buffer settings when you hit the point where you start getting crackling and/or drop-outs. Not ideal when you are tracking though - because of the latency increase. So try keep FX count down for tracking (archiving non-essential tracks while tracking can also help), and raise buffer sizes when you are mixing.

Your bread-and-butter FX, like EQ and compression, don't take many resources, but reverbs/ambience and amp/mic speaker simulation FX (especially convolution based) can be huge resource hogs. So freezing effects laden tracks can help a bit, but using effects sends for reverbs so you can keep the number of reverbs in a project down is the most effective strategy (and makes for a tighter mix).

Softsynths and samplers are your biggest culprits, so freezing them once you have the parts edited properly can be the single biggest thing you can do.

Would getting more RAM not help? Its real cheap these days. It can help take the load off

My pc is about 3 years old now... Core 2 duo 3ghz cpu with 4gig ddr2 RAM. All components are gigabyte. It was pretty top of the range when I got it.

I have my buffer size on the lowest it can go at 128, maybe I should raise that a little. I try and send as many things to busses as possible.

I'm not sure more RAM would help? I thought the CPU was where all the magic happens when it comes to mixing. Could be wrong though.

Sometimes I find the only solution is to render certain CPU heavy tracks and add them already processed to my mix. It is annoying though.. I prefer running my plugins simultaneously in one mix so that I can make adjustments easier.

Thanks for the advice, I will keep fiddling to see if I can improve performance in any way.