I agree with KerryG that Reaper's transient detection needs improving. I don't know how the algorithm works at the moment, but from what I've read one fairly reliable method is to perform an FFT analysis, and then any steep changes in the spectral slope indicate a "transient". This method is simple, and has downsides though. There is an interesting research paper which seems to suggest a more accurate method, but it explains an issue in situations where there is a smooth change in frequency, which would not be detected as a transient/onset. It seems to me that if Cockos could redesign their transient detection with the concepts of that paper in mind, and then supplement the algorithm with pitch detection (that already exists in Reaper), it would greatly improve how Reaper detects percussive transients, as well as other event onsets and transitions in audio signals.