Got this post from the Apple discussion boards:
Bare with me as this is a LONG post. I spent about 10 minutes with GarageBand today and spoke to a high level product specialist who answered some of my questions. Some things AREN'T listed here as they have been covered on this forum already.
The system is very modular. You can pick a pre made instrument, or you can choose one, change the settings (including the actual instrument of choice) and save that as a new instrument. So you have a set of actual instrument types, and then you have a set of instrument presets that have all the settings you like for that instrument. These you can change and save as much as you want.
In each preset window, you can change things like Instrument (as mentioned earlier), Compression, EQ, 2 Effects (including Audio Units), Echo and Reverb. So all this can be saved
Its a bit confusing at first because of the two different instrument types, but after a few minutes it makes sense. I only wish theyd name the presets something like Favorites instead of instruments.
There are a BUNCH of preset drum kits in there, not sure how many, but more then 10 I think. I mention this just as an extra, but they work the same as any instrument, so you can make a preset that has say, a techno set, and change the compression, echo, effect, etc.
Other things of importance
If you have a Core Audio compliant device, you can use it with GB. That means the Mbox and M-audio devices SHOULD work, as long as they are CA compatible.
You can record TWO DIFFERENT MONO tracks at a time, but only with something OTHER than Apples built-in audio input. That means if you have say, an M-audio 2 channel input device, not only can you record a stereo instrument, but you could record TWO different mono guitars at the same time to DIFFERENT tracks. Very cool.
You cannot keyframe/envelope effects. You can do this for volume, but not effects. This is expected with a consumer app. If you need super power, buy Logic.
Quantizing appears to only work to the 32nd note. I played a messy beat in with some fancy bass drum patternshitting the Fix Rhythm button actually changed my pattern quite a bit.
You CAN turn on a click track, AND a 4 count count-in to your recording (which I was HOPING was in there).
ANY midi loop or midi recorded track can be edited for pitch and beat. Plus you can view the track by Note, Modulation, Pitchbend, and Sustain, and you can do things like EDIT pitchbend using a dot and line system just like the envelopes in Soundtrack or the volume in iMovie. I assume you can change the other items using the same system. Very nice stuff.
Theres a transpose slider on each track, though I didnt play with it at all. Drum tracks also have a Velocity slider, which I didnt test.
Two kinds, Midi and AIF. Green loops mean Midi, blue loops mean Audio, and you can actually see a symbol that looks like a mini wave form for the blue loops to help you differentiate the two.
There is some crossover with the ST library, but its not a total duplication.
Loops work fine in BOTH apps because the Midi loops contain an AIF file, so they are SUPPOSED to work in Soundtrack just fine.
Midi loops are fully editable, just like a Midi track. Audio loops are just like those in ST, you cant mess with individual beats, etc.
Heres something interesting. All you get is Export to iTunes. Thankfully, its in AIF format, and NOT Mp3, so you can convert it to something else, but it will always spit the file out and drop it into your iTunes library. This confirms my thoughts that this really IS an iApp, to compliment iMovie for making songs for your movies, which will of course, be in iMovies music list since it taps the iTunes library.