Use Reatune to write audio to midi

From CockosWiki

1. Add ReaTune to the FX of the audio track you want "convert" to midi.
2. Inside Reatune check "Send MIDI events when pitch changes"
3. Go to the "I/O Routing" of the Audio track. Route it to the track where you have your midi synth, under "SENDS": Route ONLY the MIDI data "All channels to All channels". In the Audio combo box route "None to Channel 1/2"
4. Go to the "I/O Routing" of the MIDI Track. Select the Audio track in your "RECEIVES" (if you did the previous step well, it is done automatically)
5. You are done.

• Tip 1: If you want, you can select an specific midi channel instead of all them.

• Tip 2: You can put GSNAP or any other AUTOTUNE in the fx sidechain before REATUNE, to make more easy for REATUNE to recognize the pitch of your audio.