Midifier is an audio plugin that converts monophonic audio tracks to MIDI data in real-time. Using Midifier, you can control your MIDI devices vocally or with another instrument. Midifier can also act as a substitute for MIDI keyboard. How it works:

Put some audio material on one track in your sequencer, set up Midifier and a MIDI track for output, and press the play the button of your sequencer. It's that simple.

Midifier transforms the audio to MIDI notes on-the-fly. Your melody will be played back with the instrument you set up for the MIDI output track. Or you can set up Midifier to save the result of the conversion to a MIDI file.