We previously posted Ted Landau's observations of the demands of GarageBand, which can suck up a good amount of RAM and processor cycles. However, reader Johan Skaneby reports that a significant portion of GarageBand's overhead is actually due to its graphical interface, rather than its audio processing:
"When you start Process Viewer you will notice that Garageband is using a lot of processor power, nearly 90%, but when quitting the GUI it drops down to half . I have tried this on several computers, and no matter the amount of channels, the GUI demands too much of the processor."
We've verified this phenomenon here at MacFixIt. We played back a GarageBand song with eight tracks on a dual-2GHz Power Mac G5 with 1.5GB RAM. During uninterrupted, looping playback, Process Viewer reports GarageBand's processor usage as 75%-85%. If we then hide GarageBand (while the song is still playing), CPU usage immediately drops to 20-30%. Although it's common for an application's GUI to add to its processor overhead, GarageBand's GUI appears to be significantly more demanding than those of most other applications.