Signal Processing With Propellerheads' Recycle

ReCycle can do a lot more than create REX files…like signal processing.

By Craig Anderton

Propellerheads' ReCycle is a cross-platform software tool for creating REX files, which can stretch tempo and pitch independently. The process works by cutting a digital audio file into multiple slices, usually with the cut points at steep attack transients. These slices are triggered by MIDI; as the tempo of the host DAW or sequencer slows down, the slices are triggered further apart, thus slowing down the phrase. Faster tempos trigger the slices closer together. (Pitch transposition is a separate process that, while not as effective as time-stretching, is satisfactory for relatively small transposition ranges.)

The REX time-stretching process is optimized for sounds like drums, percussion, and other instruments with sharp, defined transients. But for groove-oriented music, ReCycle can also be a wonderful processor for imparting "synchro-sonic" (beat-related) characteristics to sustained sounds. I used this technique a lot with guitar power chord samples on the Technoid Guitars sample CD so they could pulse with the beat instead of just sustain -- think of it as 21st century, synchronized tremolo. However, this technique also works with vocals, bass, string parts, and just about anything that sustains.

We'll start with creative signal chopping, then move on to some other ReCycle processing tricks.

RHYTHMIC CHOPPING

Suppose there's some audio in your DAW program, like a sustained chord, phrase with multiple chords, vocals, or the like, and you want to create a 16th note tremolo effect that chops the sound. Define the region of audio you want to process (make sure the boundaries fall precisely on beats, and note the total duration in measures + beats). Then, export the region as AIFF or WAV audio, 16 or 24 bits. Open the file in ReCycle, then:

1.  Go View > Show Grid. Enter the duration in bars.

2.  A grid appears, with sub-divisions for 16th notes.

3.  Go Process > Add Slices to Grid. This adds slices at every 16th note.

4.  Click on the "Preview Toggle" icon.

5.  Click "Play." You'll hear the original sound with small gaps, and possibly clicks, at the slices. If you like this sound, fine. But let's click on the Envelope icon, then refine the sound further with the envelope options.

6.  Use the envelope Decay control to edit the slice decay time (try around 300 ms to start). When you click on "Play," you'll hear a decaying sound every 16th note.

7.  Experiment with the Attack control. A 1.0 ms setting minimizes clicking at the slice points; longer settings give an "attack delay" effect, where each slice fades up to maximum.

8. If you plan to stretch the audio to a different tempo, slow it to the minimum tempo you expect to use, and adjust the Stretch control to obtain the best possible sound quality. Also check it at the highest anticipated tempo, and choose a Stretch setting that gives a good overall compromise sound.

Done! If you save this file, it will be in REX format, suitable for use in supporting programs like Reason, Cubase, Logic, Sonar, etc. However, you don't have to save it as a REX file; you can export as a WAV, AIFF, or SD II file, then simply bring it back into the program from which it came. To do this:

1. Go Process > Transmit As One Sample before saving. Otherwise, each slice will be saved as an individual file.

2. Go File > Export, and choose the file type.

3. Click on Save.

ADVANCED CHOPPING

Slices need not be on rigid boundaries, nor constrained to the grid. So, you can easily create syncopated patterns, or place the emphasis on certain beats -- like having the longest slice on the downbeat. Just place the marker where you want a slice to start, or use the hide function (click on the Hide icon, which looks like an X) to turn off a marker if you want a longer slice.

There's even a way to create gaps and stuttering effects, because ReCycle lets you mute any number of slices. Select the Pencil tool, then click on the marker that begins a slice to be muted (or Shift-click for multiple markers). Click on the Silence Selected icon or go Process > Silence Selected. This mutes the slice following each selected marker. If you export the file, there will be silence wherever the slice was muted.

This shows a file before and after processing. The top file is the original audio; note where the markers were placed in ReCycle. The lighter section represents a slice that was muted. The lower file shows the results of exporting as an AIFF file, with a fairly short Decay setting. The red lines were added to emphasize how the audio waveform lines up with the ReCycle markers. Note how the original sustained chord is now a series of rhythmic pulses.

ANOTHER GAPPING OPTION

You can also create gap/stutter effects very easily, albeit not with the same kind of rhythmic precision as the previously-described methods, just by editing the Gate Sensitivity parameter. This applies a gating effect to individual slices that turns on at the start of the slice, and mutes the signal when the level falls below the Sensitivity threshold.

Actually, the process is a little more complex than this, because even slices with all levels below the threshold may have a little signal present at the start of the slice. But don't worry about the fine points; just play the file, adjust the Sensitivity, and if it makes groovacious sounds, you're set.

SLICE JUMBLING

Although you'll usually want to save a file as a single entity, if you uncheck Process > Transmit as One Sample, each slice will be saved as an individual file. These can then be re-assembled in your DAW. For the most foolproof results when re-assembling, before saving slice at equal intervals like 8th or 16th notes (although the adventurous are welcome to experiment).

These slices are numbered, so it's easy to bring them back into your DAW in the original order (for best results, choose an appropriate snap value; some snap functions allow snapping to event boundaries, which makes it simple to "butt splice" the various slices together). But why be normal? Change the order of the slices within your DAW, remove slices, duplicate slices, snap them to different beats, etc.

THE OTHER KIND OF NORMALIZATION

ReCycle can normalize a file (usually done before slicing, but it can be done afterward as well). However, go Process > Normalize and you'll see two options: normalize Each Slice or the Whole File. If you normalize all individual slices, this can bring up soft parts and alter dynamics in interesting ways.

A HOME FOR TRANSIENTS

Finally, don't overlook the Transient Shaper as another useful processor. Superficially it resembles a compressor, but it works on a different principle. Rather than burn up a lot of words here describing it, I suggest learning about it by checking out the supplied presets, and tweaking them to see how the controls affect the sound.

Note that using these processors may change the gain, possibly causing clipping. Periodically check the meters in the lower right corner of the main sample window, and adjust the Gain control for the highest signal level short of distortion.

Yes, ReCycle can do a lot more than create REX files -- especially for beat-oriented music. Mess around with it, and the results may surprise you.

Craig Anderton is Editor Emeritus of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.