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Converting Guitar Signals to MIDI Data

August 18, 2014
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Converting guitar audio to MIDI isn’t easy, but Celemony’s Melodyne pitch-correction and note-editing software takes the process up another notch. Melodyne can live within a host DAW as a plug-in, run standalone, or, more interestingly, integrate closely with DAWs through the Audio Random Access (ARA) protocol. ARA, which exchanges information about audio clips (tempo, rhythm, pitch, and more) with Melodyne was developed by Celemony and PreSonus. ARA opens up several possibilities, but we’ll focus on audio-to- MIDI conversion.

PreSonus Studio One Pro 2 and Cakewalk Sonar X3 currently integrate ARA, and both come with Melodyne Essential (a.k.a. Melodyne Singletrack), which does monophonic note editing. I expect most other developers will integrate ARA in the near future.

Here’s how the process works:

• Record an audio track. Play single-note lines, and, as with any audio-to-MIDI conversion, play as cleanly as possible. Melodyne Singletrack will not translate pitch bend or slides, so avoid both. You can add pitch bend later by editing the MIDI data.

• Define the clip as a Melodyne region. In Sonar, right-click on the clip, and choose Region FX > Melodyne > Create Region FX. In Studio One Pro 2, select the clip, and then—from the menu bar— choose Audio > Edit with Melodyne.

• Melodyne will analyze the audio, and then open its interface.

• If there are any incorrect notes, you can fix them now, or fix them later when they’re MIDI data.

• Insert a virtual instrument. For example, I like playing bass parts on guitar or bass to drive a big Minimoog-type synth sound.

• Drag the clip that has been analyzed into the virtual instrument’s MIDI track. This converts the audio into MIDI data automatically.

Now you can edit the MIDI data to clean it up if needed, and—voilà—instant MIDI instrument.

If you want to take matters further, Melodyne Editor ($399) does polyphonic note detection, as well as MIDI conversion, and the multitrack Melodyne Studio ($699) has additional MIDI features, such as adding MIDI pitch-bend data for pitch drift and modulation, envelope creation, and velocity curves. However, note that polyphonic conversion to MIDI requires some work to clean everything up. Celemony has posted an informative video about extracting polyphonic MIDI data from guitars on its website’s Help Center.

Of course, another—albeit time-consuming—approach to polyphonic material is to break chords down into single-note lines, convert each to a MIDI track, and then merge the MIDI tracks together.

Craig Anderton has played on or produced more than 20 major label releases, mastered hundreds of tracks, and written dozens of books. Check out some of his latest music at youtube.com/thecraiganderton.

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