Loops aren’t just for DJs—more musicians of all types use
loops for anything from a rhythmic backbone to interesting sweetening.
But if you think using loops simply means slapping them into a DAW’s
track or loading them into a sampler, you’re not taking full advantage
of what loops can do—and they can do a lot!
Choose the right loop format for the job. There are
three main stretchable loop types. REX files detect the transients in a
piece of audio, create “slices” at these transients, and associate each
slice with a MIDI note. These MIDI notes form a sequence that plays the
slices sequentially; so speeding up the sequence speeds up the rate at
which the slices play back, thus increasing the tempo. The reverse
happens when you slow down the sequence. REX files are ideal for
percussive tracks, particularly if they aren’t melodic and don’t have
sustained sounds (e.g., cymbal crashes). Single-note lines, like
bass, sometimes stretch well, too. REX files can have excellent sound
quality, as slicing the audio doesn’t change the fidelity, only the
duration; however, slowing down can leave gaps between the slices that
may or may not be problematic. Changing a REX file’s pitch applies DSP;
the quality of the results depends mostly on the transposition amount.
The Acidized and Apple Loops formats also detect
transients but instead of slicing the audio physically, they employ DSP
to lengthen these sections to slow down tempo (or shorten them to speed
up). To avoid discontinuities in the transitions between sections,
Acidized and Apple Loops files apply crossfading to smooth the sound.
The files don’t always work as well with percussive material as the REX
format, but often do a superior job with sustained sounds or sounds
where you need to transpose pitch.
Tools for rolling your own. Creating or editing REX
files requires Propellerhead ReCycle; you can create or edit Acidized
files in any version of Sony Acid or Cakewalk Sonar. To obtain a utility
program for working with Apple Loops, register as an Apple developer
(it’s free) at https://developer.apple.com/downloads/,
then search for “Apple Loops” and download the Apple Loops Utility SDK.
Note that with any of these formats, creating stretchable files capable
of working over a wide tempo range is a very specialized skill—so
expect to do lots of trial and error. Also note that unfortunately, many
loop libraries have shoddy enough editing that you may need to edit
files yourself for best results.
Another option is simply to use a DAW’s stretching DSP to
trim an audio file to the right length, and therefore the right tempo.
For example, if a file is a little too long in Cubase, you control-click
on the edge of the audio file and drag until it’s the proper length.
However unlike stretchable file formats, files stretched via DSP will
not react to tempo changes.
The magic of 100 bpm. Stretchable
loop formats have a much easier time speeding up than slowing down
because speeding up removes material, while slowing down has to create
new material. It’s often possible to speed up the tempo by 150 percent
(or more) with a properly edited file, but only slow down by 10 to 20
percent. So, record files you want to loop at 100 bpm in order to slide
down into the 80 bpm hip-hop range, or speed up to almost the
A deranged Acidized file trick. Want some robotic
electro loops? In Sonar, double-click on a loop to bring up the Loop
Construction window. Set the Pitch transpose parameter to +24 (but be
sure to try other settings), Threshold to 100 percent, and start playing
the loop (see Figure 1). Next, experiment with the rhythmic
value in the drop-down menu to the left of the Threshold slider. Start
with 32nd-notes for the most robotic/metallic effect, then try
sixteenth-notes, eighths, and so on. Each slice setting produces a
different type of freakazoid effect; you can further modify the sound
with the Threshold slider. These bizarro loops seem most effective when
layered with the original loop, which should be set to normal loop
settings. They also make great breakbeats when you drop out the original
Create “faux REX” files. Set your DAW to the same
tempo as the audio clip you want to slice (make sure the clip sits on
measure boundaries), and then slice the audio at transients. As these
slices will “anchor” to specific places on the DAW’s timeline, speeding
up or slowing down the DAW’s tempo will change the speed at which these
slices play back (see Figure 2). However, they won’t be MIDI-triggerable unless you map each slice to a sampler’s key (e.g., using Native Instruments Kontakt, MOTU MachFive, Reason’s NN-XT, or another soft sampler).
Loop virtually any pad sound. The tools to create
perfect “pad loops” exist in most DAWs. We’ll assume you’ll want to
retain the pad’s attack, having the loop occur within the pad’s sustain.
As pads don’t have rhythmic components, it usually doesn’t matter how
long a section of the sustained part you loop. For this example, we’ll
loop the last three bars of a four-bar pad.
Record a little more than four bars of the pad, then split
the file at the start of measure 2 and the start of measure 5. Delete
everything after measure 5. Next, copy measure 1 and slide it over
measure 4 of the pad to create a crossfade (preferably with an
equal-power fade curve as in Figure 3). If your DAW doesn’t
create crossfades automatically, then add a convex fade-in to the copy
of measure 1 and a convex fade-out over measure 4, then mix the measure 1
copy with measure 4.
In a DAW, you can copy/paste measures 2 through 4 to
extend the loop. In a sampler, bounce what you created into a single
audio file, and then import this into your sampler. Set the loop end at
the end of the file, and the loop start at the precise start of measure 2
(this may require some experimentation). When you play a key, you’ll
hear the pad attack, then the pad’s sustain will loop.
The REX jumble. One of the
coolest features of REX files (and even “faux REX” files if they’re
triggerable via MIDI) is that you can rearrange the MIDI notes to
trigger slices non-sequentially. Slices in drum loops will often isolate
individual elements—kick, hi-hat, snare, and the like—and you can
change these around to change a drum pattern (see Figure 4).