Just a quick question...

I do lots of recording with MIDI and VST stuff. I was just wondering...is it possible to extract MIDI from mp3 or another audio source?
In theory, yes... but it has to be very clean audio and it is only likely to work with any accuracy if it is single-notes rather than chords. If you mean the .mp3 of a fully-mastered song with all the elements mixed down to a single stereo file though - the answer is a resound 'no'.
Hey, look. Sigs are back.
I'm not trying to get notes and chords and all that...just hat, snare and bass drums. Just the basic structure to tweak. Something to work from. I'm thinking that if a load a track into Reaper, EQ it to hell and back to single out the hat, snare and bass drums and use Trigger, I might be able to do it but I haven't had a chance to mess with it yet. Wondering if anyone had any ideas on how to do it, if it's possible at all.

Like you said though, I think trying to get guitar or bass from a song would be all but impossible...
Trigger will probably work, if you filter out as much as you can of the unwanted stuff (doing so for the hi-hat will be quite tricky though, in particular) but I wouldn't expect anything incredible if the song is a commercial release, as it will already have been compressed/limited to hell and back, making it a lot harder for Trigger (or any other transient-detection program) to pinpoint the attack of the hits, and distinguish them from the rest of the mix.
Hey, look. Sigs are back.
Yea...I'm messing with it now. Downloaded a trigger plugin called DST Trigger Free and I'm tinkering with it. I MIGHT be able to do it. Dunno. If I could even just get the bass drum and the snare, that would work. We shall see.

Anyone else have any ideas?

I did it!

...ok...ok...it's in the works, but it'll work. Here's how -

1st way is to CRANK UP a noise gate so ONLY the bass and snare hits come through. From there I can run it through that free trigger thing I mentioned and it picks it up just fine.

2nd way is using a program called Beat to MIDI. It's basically the same idea as before but might be a bit more flexible and/or dynamic. I'll have to see tomorrow. Thanks man!