MIDI Tricks: Voice Splitting and Rotating

Assigning a unique instrument or choral voice to each part in

The original four-part MIDI clip (upper left) is split into a unique MIDI clip for each voice (upper middle), and then voice 1 is divided into two parts by rotation. In the lower section, all parts have been split and rotated together so that each part is played by a different voice in each chord.

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ASSIGNING A unique instrument or choral voice to each part in a polyphonic score is as old as polyphony itself. But, in a technology dominated by keyboard input and polyphonic MIDI sequencing, realizing separate parts is not always a matter of simply scoring or recording them separately—for example, you might be starting with polyphonic MIDI clips from a collaborator or library, or you may achieve a better performance by playing them polyphonically on your keyboard. Still, splitting polyphonic parts is well worth the extra effort. Here are a few ways it expands your options.

Splitting The most common way to route notes within a MIDI clip to separate instruments is to assign the notes to different MIDI channels so that multitimbral samplers and synths can route them automatically. Among DAWs that support MIDI channels, Apple Logic stands out by making channel-splitting dead-simple with its Voices to Channels function.

Splitting a polyphonic MIDI clip into a separate MIDI clip for each voice is a more flexible approach, and it has the advantage of working in DAWs such as Ableton Live and Propellerhead Reason that don’t support MIDI channels. The process is no more tedious than manually assigning notes to individual channels, and it allows many more options in editing and routing parts: You can apply separate automation, offset parts in time, double some parts, and so on. For example, try doubling the top part one or more times with a different sound, volume and pan automation, and differing time offsets to produce a multitimbral echo-like effect.

Rotating Once you’ve split a polyphonic clip into monophonic parts, you might try routing consecutive notes to different sounds—a process called rotation. That often works well with inner voices while preserving the integrity of the melody and bass. As with splitting, you can use MIDI channels or separate clips for rotation.

You can often combine splitting and rotating for polyphonic clips. For example, you might rotate the top-down voice assignments for each new chord, or you might rotate just the assignments of the inner voices. Keep in mind that you may run into problems if the individual voices are pitch-range limited (choral voices, sax or string sections, and such).

(Almost) Free Lunch None of the processes described above are realtime, but if you nose around a bit you’ll find various tools for automatically rerouting both sequenced and realtime MIDI input. For example, a couple of inexpensive Rack Extensions for Reason, Blamsoft Distributor and Jiggery-Pokery Charlotte, make quick work of splitting and rotating up to eight MIDI voices. Distributor routes notes in the order received. A variety of controls affect voice selection, but you must slightly offset notes manually to control the voice order. Charlotte waits for the whole chord, using an adjustable wait time, and it allows you to select note priority (high, low, first, last, and so on). If you’re so inclined, you might also try designing your own splitters and rotators in applications like Cycling ’74 Max/MSP, Plogue Bidule, Logic’s Environment, and Native Instruments Reaktor.

Len Sasso is a contributing editor at Electronic Musician.