And if you're a guitarist like me (I use the term "guitarist" loosely; I'm way ahead of my five-year-old nephew, though my 15-year-old son is gaining on me. Either way, Jimi Hendrix's legacy is safe), you can plug right into your Mac with a 1/4"-1/8" audio jack adapter and use any of the 15 classic guitar amp presets, which run the gamut from Byrds-y electric 12-string to Nirvana-esque grunge. That's the beauty and the danger of GarageBand: if you're a professional musician, GarageBand and Jam Pack give you easy access to more instruments than you could probably afford if you bought the real deals. If you're an amateur like me, it's easy enough to fool yourself into thinking you sound like a pro.
You build audio compositions in GarageBand similarly to the way you build them in any loop-based music creation tool. Click the Browse button to display the loops available, then drag the ones you want into the Track window, where you can adjust duration, pitch, and volume. If you're adding original guitar, plug in and select the amp sound you want, add any of the dozens of effects (chorus, flanger, distortion, etc.), and then play along live with the track you've created from the loops.
For USB keyboard, the process is pretty much the same, and GarageBand gives you pinpoint control over the final sound via compression, equalization, echo, reverb, and other filters. And if you want to add a vocal track, you can plug one into the Mac's sound input jack or run it through a USB interface (not included). Once you've input your performance, you can go into the editor window and modify it, adjusting the speed, sustain, and pitch of each note you played, so if you lay down a screaming guitar solo that's marred by one bad note, there's no need to re-record it. The Fix Timing button lets you lock in your notes to the "click track" (somewhere, Frank Zappa is turning over in his grave) for beat-perfect performances.
As for the software instruments themselves, they're virtually all terrific, from the Stevie Wonder-style "dark clavinet" (think of the beginning of "Superstition," and you can hear exactly what that sounds like) to the wide variety of synthesizer tones and range of simulated bass sounds. The only disappointment is a predictable one: the horns and woodwinds sound lifeless and, well, software-generated. But that's true for all but the highest-end synthesizer. For all the control a good MIDI keyboard will give you, it will never allow you to simulate the dynamics of the sounds made by a real horn or wind player.
When your track is complete, you can export it to iTunes as an AIFF file with one click. From there, of course, it's easy to use it with any of the other iLife apps, as well as Soundtrack or either the Pro or Express version of Final Cut.
Even on its own, GarageBand supplies plenty of options to keep musicians and soundtrack creators busy. With the addition of the JamPack, the possibilities are darned near endless. Now if only Apple could somehow find a way to package the gasoline smell or the sound of your neighbors telling you to keep it down.
System requirements: 600mHz G3 (G4 or G5 required for software instruments); Mac OS X 10.2.6 or later; QuickTime 6.4 or later; 256MB RAM