Audio-to-Score takes a bit of getting used to, but it can do a really good job of translating audio transients (and even pitches) into a series of corresponding MIDI notes. How well it works is dependent on careful setting of the various parameters.
As far as beat mapping goes, the process for doing what you want is a little lengthy to explain, but here goes!
The process involves:
- beat mapping the section of audio that you want to emulate the groove of
- recording a MIDI part which will be quantized to the tempo changes generated from beat mapping that part
- doing a bunch of operations to finalize what is to become your groove template
First, SMPTE-lock all regions in your song. This will prevent things from shifting around as you do your beat mapping operations.
The next step is to open the global beat mapping track, select the audio track playing the groove, and hit "analyze". Now you're going to beat map the section of audio playing the groove you want to emulate. You'll have to judge for yourself how much beat mapping is necessary. For example, if it's an 8th note groove, be sure to map every 8th note in that section of the track. This will result in a tempo map where the tempo changes every 8th note.
Next... on an instrument track, load up a sound -- something percussive or with a sharp attack -- and record yourself playing along with the groove. Your timing doesn't have to be perfect, though it should be close. Now, quantize that MIDI part (in this case, to 8th notes) and its notes will conform to the timing of the tempo map. Play back the track to ensure that your MIDI instrument sound plays tightly with the track. If it doesn't, you may have to fine-tune the position of the beat mapping lines in certain areas.
The final steps: SMPTE-lock the MIDI region and delete all of the beat mapping lines except for the first one. If you do it right you'll end up with only one tempo -- the original tempo of your track (view the tempo list to be sure). Now SMPTE-unlock everything and use that MIDI region as a Groove Template.