KTDrumTrigger

KTDrumTrigger was developed to be a VST plugin with custom editor that triggers MIDI notes based on the sound level of the incoming audio stream in different frequency bands. It allows you to "detect" occurrences of percussive sounds in an audio stream and send out a MIDI event whenever that happens.

It works like this: incoming (mono) audio is split up into different frequency bands using three tweakable filters. The signal in each of these bands is sent through an envelope follower. When the envelope reaches a specified threshold level, a MIDI note on message is generated. The trigger module has some built-in hysteresis and minimum inter onset time settings to avoid fast successive triggers due to noise on the envelope curves. Visual feedback of the filter and trigger settings is available....

Note that this is a rather simple system for finding drum onsets in an audio stream. It will probably only work reliably on isolated drum tracks (no mixed-in music), it's quite sensitive to volume changes and it might not always be possible to separate the different types of drum sounds using simple filters. However, if you just need a fast way of transcribing your isolated drum tracks into MIDI so you can tweak them further or apply the groove to other parts, it might well do the trick and save you a lot of time.