Loop Microsurgery

Microsurgical editing can enhance the musicality and groove quotient of your loops. All you need is an audio editor with a few standard effects (EQ, filtering,
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Microsurgical editing can enhance the musicality and groove quotient of your loops. All you need is an audio editor with a few standard effects (EQ, filtering, reverb, amplitude envelope, and reverse). I use Sound Forge, but any editor will do as long as it lets you zoom in on the sample level.

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Fig. 1: Shown here is a loop that has been sliced up in Sound Forge and is ready for microsurgical editing.

The basic process is simple: divide your loop into slices, and then edit them. Slices should be single events — a beat, a note, an impulse, for example. In essence, you'll be beat slicing, but you'll be doing it manually, and that will afford you greater editing flexibility.

Slice It Up

The first step is to divide your loop into slices, one for each audible event (see Fig. 1). Work through the loop from beginning to end, listening carefully for event attacks. At each attack, zoom in to a high resolution and locate the exact onset of the attack, which should show up as a sudden waveform change. Then zoom out to the sample level, find the nearest zero crossing before the event attack, and mark it to begin the slice. Continue that process until the entire loop is divided into slices. The beginning of each slice serves as the end of the previous one, so if you choose not to mark all slices, you may need to mark endpoints as well.

Be sure to save a copy of the sliced-up loop, because it is the starting point for all your microsurgical editing. That will allow you to experiment without having to re-create slices.

Rearrange Your Slices

Once you've marked your slices, you can begin editing, and slice rearrangement is a great starting point. You can change the nature of your loop subtly or dramatically by rearranging its slices. You can move a slice to a different location in the loop. You can replace one slice with another from the same loop or from a different source. You can insert a slice or delete one. Finally, you can mute a slice by either replacing it with silence or, if that proves too musically jolting, with background noise, which you can often harvest from another part of the loop.

Before rearranging slices, it's important to decide whether to work destructively or nondestructively. Destructive editing alters the length of the loop. For example, if you insert two 8th-note events into a 4/4 loop, you'll end up with a 5/4 loop. Nondestructive editing leaves the loop length intact. For example, if you mute two 8th-note events in a 4/4 loop, you'll end up with the same 4/4 loop with two 8th-note holes (silences) in it.

Nondestructive editing (see Web Clip 1) leaves the meter, tempo, and pulse intact, making it well suited for fixed-beat styles such as house, trance, and tribal. Destructive editing (see Web Clip 2) changes the loop meter and, in some cases, tempo and pulse, which makes it more appropriate for polymetric, free-form, or experimental music.

Add Effects to Your Slices

You can also add effects to your slices (see Web Clip 3), either individually or in groups. For example, you might reverse one slice, apply a highpass filter to the next, a lowpass filter to the one after that, and then select all three as a multi-slice group and apply reverb. Or you might apply different flanging to a succession of contiguous slices, then select the entire group and apply an amplitude envelope.

You can use most effects nondestructively. Equalizing, filtering, amplitude enveloping, and short-delay-time effects (phasing, flanging, and chorus) leave the slice and loop length intact. Time-stretching slices will alter the loop length if you move the surrounding slices to accommodate the stretched slice's duration. The same principle applies to reverb, echo, and long-delay effects. For example, applying reverb to the last event in a loop will lengthen the loop by the duration of the reverb tail unless you truncate it unnaturally.

Any process that you apply to an audio clip as a whole is fair game for altering individual slices in your loops. The only thing you need to watch out for is the impact of that processing on slice length.

rachMiel is a composer of experimental electronic and acoustic music. He can be contacted through his Web site atwww.rachmiel.com.