Tips and Tricks for Loops and Beats
By Craig Anderton
Tue, 21 Jan 2014
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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! 

       
 Fig. 1. Using the “wrong” loop settings can create metallic, robotic effects in Cakewalk Sonar.  Fig. 2. A 120 bpm, two-measure loop has been sliced with Logic’s tempo set to 120 bpm. Slowing the tempo down to 100 bpm spaces out the slices, but the overall duration is still two measures.

Fig. 3. The top view shows the original waveform, with a split at measure 2. The middle view shows the copied measure about to be crossfaded with the waveform’s final measure, as shown in the lower view. The yellow line at the top indicates the loop points.


 
Fig. 4. Reason’s Dr. OctoRex can send the MIDI notes that trigger slices to a track, making it easy to rearrange the MIDI notes and thus change the loop’s arrangement. Note how the first two measures have had their notes modified in the second two measures.

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 drum-and-bass zone.


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 loop.


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).

 
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