Feb 1, 2010 12:00 PM, By Jim Aikin

THE DAWN OF POLYPHONIC PITCH CORRECTION

Polyphonic Audio Editing

With polyphonic tracks, the process of editing Melodyne's analysis so as to identify the right notes can be quite fiddly — and it's easy to see why. After analyzing the frequency content of the audio, the plug-in has to decide which sine wave partials belong to which notes. The software will sometimes think that prominent overtones are separate notes or will skip notes because it thinks they're overtones. It can also interpret small artifacts as the beginnings of new notes or miss low-level areas within a long note, turning it into two separated notes.

Two sliders help you with the analysis: One adds more “possible” notes (grayed out) to the display and the other changes the threshold that turns possible notes into actual detected notes. Notes can be activated or deactivated (returned to the “possibles” category) by double-clicking. As you mouse over a region, a gray haze indicates sonic energy that Melodyne didn't even consider a possible note. You can turn this into an analyzed note by double-clicking. Once the analysis is complete, you proceed to the normal editing process, changing note pitches and so on.

For an acid test, I tuned a steel-string acoustic guitar carefully and then deliberately tuned the G string flat and strummed four sustained chords. About five minutes of hand editing were needed to guide Melodyne to all of the notes in the chords — and that was with an audio clip less than 15 seconds long. Hand-correcting the analysis of a three-minute guitar track with lots of strumming would take literally hours.

I then attempted to correct my out-of-tune notes. Dragging them up to concert pitch was easy, but the result didn't sound pleasant or natural. My theory about the difficulty is this: Even though I told Melodyne where the fundamentals of the out-of-tune notes were, it was still identifying certain overtones within those notes as belonging to other notes, which meant that it didn't move the overtones when I moved the fundamental. With a guitar chord, one string is likely to be doubling another string at the octave, so this type of confusion is almost inevitable. The note that sounded best after editing (the G sharp in an open-position E major chord) was one that wasn't doubled at an octave.

Perfect Pitch

Melodyne Editor is my go-to software for fixing pitch problems in monophonic audio. It's easy to use, has powerful tools and sounds great. DNA could be very useful in a few situations, such as fixing a flubbed note in a piano track, but it's not magic. In many cases, you'll probably get better results (and just as quickly) by having the musician do a punch or re-record the track. Still, this is the roll-out of an entirely new technology. The future of DNA looks very promising.

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