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Master Class: By the Slice

July 1, 2009
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Get added mileage out of your library of sliced audio files by playing their slices using a step sequencer or arpeggiator. Either option is more interactive than triggering the slices from a MIDI file. And because audio file slicing is easily done in most DAWs and sample editors, you can adapt this process to any file in your arsenal.

Step sequencing and arpeggiation are, by their nature, grid-based; steps are timed to note divisions. Therefore, working with grid-sliced audio will most closely align the results with the original, but that's no reason to limit yourself to grid slicing. Event-sliced audio, in which each slice holds a complete audio event such as a note or short phrase, often makes equally good fodder. Here, I'll illustrate both approaches using the step sequencers, arpeggiators and sample players in a variety of software applications.

Within Reason

If you're a Propellerhead Reason 4 user, then you have all the tools for both step-sequencing and arpeggiating sliced audio, and you have a lot of REX files with which to work in the factory library. The Dr.REX Loop Player is the obvious first choice for playing REX files, although Reason sample players NN19, NN-XT and Redrum offer useful playback options. The RPG-8 arpeggiator and the Matrix step sequencer are the logical choices for slice triggering, but the step sequencers in Redrum and the Thor Polysonic Synthesizer are viable alternatives.

FIG. 1: This Matrix sequence of tied 16th notes plays the Dr.REX slices in their original order and eighth-note timing, while its Curve pattern (not shown) manipulates the Dr.REX filter cut-off.

FIG. 1: This Matrix sequence of tied 16th notes plays the Dr.REX slices in their original order and eighth-note timing, while its Curve pattern (not shown) manipulates the Dr.REX filter cut-off.

In Dr.REX, slices are triggered in left-to-right order by notes ascending from C1, MIDI note number 36. Dr.REX does not have gate and CV inputs for triggering individual slices, so circumvent that by encasing it in a Combinator and using the Combinator's gate and CV inputs. To make use of those, ensure that Receive Notes is enabled for Dr.REX in the Combinator's Programmer and cable the trigger module's outputs to the Combinator's inputs. (The trigger module does not need to be inside the Combinator.)

Working with Matrix is similar to using a trigger file on a sequencer track — you manage the trigger notes in a piano roll-style display (see Fig. 1). You cannot freely move notes in time, but you can shift them by whatever Matrix resolution (aka, step size) you choose. To ensure that the full slice plays at each step, create tied gates in Matrix by setting their velocity bars while holding the Shift key. Note that the velocity settings on Dr.REX determine whether the velocity bar values have any effect. Tied gates also ensure that consecutive steps used for the same slice will not retrigger. You can activate the Matrix Shuffle button to apply the song's global shuffle to patterns, but bear in mind that in Reason, shuffle is always 16th-note based.

One advantage to using a Matrix is that it can store up to 32 patterns, and you can automate pattern changes on a sequencer track. If the Matrix is inside the Combinator, you might assign a Combinator knob to select the pattern and then assign a MIDI controller to that knob. Don't forget that each Matrix Note pattern has an associated Curve pattern, which you can use to modulate other Dr.REX parameters such as filter cut-off (see Web Clip 1).

A Chord Apart

The hookup for the RPG-8 arpeggiator with Dr.REX or Redrum is the same as for Matrix except that if RPG-8 is inside the Combinator, then you need to ensure that Receive Notes for the RPG-8 is disabled (unchecked) in the Programmer. Otherwise, notes played by RPG-8 will be fed back and will prevent it from working properly. You also need to have a sequencer track for RPG-8 to feed it notes.

Redrum presents an interesting alternative to Dr.REX because you can load individual slices from one or more REX files into its pads, and because the individual pad controls differ from each other and from the individual slice settings in Dr.REX. That lets you cull the slices that are best for sequencing or arpeggiating and allocate them to the pads with the most useful options. Furthermore, each pad has a pair of effects sends and an optional separate output, greatly expanding the processing possibilities.

RPG-8 offers all the standard arpeggiator features and a couple of helpful extras: some unusual arpeggiation insert modes and a pattern sequencer with up to 16 steps. Insert modes 3-1 and 4-2 modify the chosen arpeggiation pattern by jumping one or two steps back in the pattern for every three or four steps forward. You use the pattern sequencer to insert rests (not to silence steps) in the arpeggiation pattern.

In Web Clip 2, I loaded 10 slices from a 30-slice piano loop into Redrum's 10 pads. I used the individual pad controls to shorten each slice to make them staccato; retune some of them; balance their levels; pan odd-numbered pads left and even-numbered ones right; and send the odd- and even-numbered pads to reverb and delay effects, respectively. I then used 4-2 insert mode and a 14-step pattern to create variations on upward arpeggiation.

The RPG-8 also serves as a MIDI-to-CV converter, allowing you to route MIDI mod wheel, pitch bend, aftertouch, expression and breath controller messages to Reason-device CV inputs. You can route these directly to Redrum, Dr.REX and effects-processor inputs or to a Combinator's modulation inputs, which you would then route using the Combinator's Programmer.

Going Live

Two features make Ableton Live 8 a standout for slice arpeggiation: It will automatically slice your audio files and create a slice-playback instrument with one mouse-click, and it has a high-powered arpeggiator. Live doesn't have a built-in step sequencer, although some are likely to appear when Cycling '74 Max for Live arrives. For the time being, you can build your own basic model using Live's MIDI effects (see the Sound Design Workshop “A Step in Time” in the November 2008 issue of EM) or use an external software or hardware step sequencer.

FIG. 2: Live devotes a Drum Rack pad to each slice and inserts a Simpler instrument into the associated chain to play the slice.

FIG. 2: Live devotes a Drum Rack pad to each slice and inserts a Simpler instrument into the associated chain to play the slice.

Live lets you slice an audio file by transients, gridlines or Warp markers. For grid-based slicing, you'll get better results by converting the transient markers closest to the gridlines to Warp markers and then slicing by those. (Double-clicking a transient marker converts it to a Warp marker.) You may need to move some transient markers slightly — which you do by Shift-clicking and dragging — to avoid clipping off the beginning of a sound. You don't need to move the Warp markers to gridlines, but triggering them with an arpeggiator or step sequencer has the same quantizing effect on the groove.

Once your Warp markers are in place, select Slice to New MIDI Track from Live's Create menu or from the clip or Clip view's Context menu (see Fig. 2). The ensuing dialog lets you choose the slicing method (choose Warp Marker) and a slicing preset. Slicing presets tell Live how to create the Drum Rack instrument that plays the slices. The two factory choices — Built-in and Built-in 0-Vel — work well; the latter ensures that each slice plays at its original level rather than being influenced by the velocity of the triggering note. Examine the presets and store your own in Library > Defaults > Slicing. I've included the one I prefer in Web Clip 3. Keep in mind that Drum Racks can hold send effects, so you can route individual pads to any combination of effects.

In the Event

For event-based slicing, as in the Redrum example, convert the transient markers for the events you want to capture to Warp markers. Again, you may need to adjust some transient markers. When you slice the file, you'll most likely have events that extend into unwanted territory. Fix that by adjusting the length settings for the Simpler instruments used to play each of the clips. Note that warping and tempo synchronization of the audio clip does not transfer to the slices — they play back as recorded. But if you move the audio clip to the Arrangement view and consolidate it (Command + J), that will lock in the warping and tempo, and you can then move the clip back to Session view for slicing.

Live's arpeggiator is easy to set up. Insert it before the Drum Rack holding your slices, and then set the Rate knob to match the size of your slices, set the Gate knob to 100 percent, dial in the desired number of repeats and choose from among the 18 styles. The Thumb, Pinky, Converge, Diverge, Random Other and Random Once styles are interesting choices for slice sequencing (see Web Clip 4). Random Other ensures that each incoming note is played before any are repeated, and Random Once repeats the same random pattern until the incoming notes change. If Hold is on (I assign a MIDI footswitch to it) and you continue to press at least one key, playing other notes toggles them in and out of the arpeggio.

By the Numbers

For a full-featured software step sequencer on a Mac, it's hard to beat Five12 Numerology 2 ($119). It's a stand-alone program that hosts Audio Units plug-ins and can sync to your DAW as a ReWire slave or using MIDI Clock. Pair it with a slice player, and you have a complete multitrack slice-sequencing solution.

FIG. 3: The drum loop shown in pHATmatik Pro has a quarter-note slice at each end and half-note slices in the middle. The Mono Note Sequencer''s StepLen settings ensure proper note-length playback.

FIG. 3: The drum loop shown in pHATmatik Pro has a quarter-note slice at each end and half-note slices in the middle. The Mono Note Sequencer''s StepLen settings ensure proper note-length playback.

Numerology tracks are tied to virtual racks of gear called Stacks. The simplest Stack for slice sequencing comprises the monophonic step sequencer, Mono Note and any Audio Units plug-in that will play sliced audio files. Here, I'll use iZotope pHATmatik Pro ($149.99), which plays REX files and lets you slice your own audio.

Beyond pitch, velocity and gate length, Mono Note gives you four individual step parameters: Groove (nudge the step early or late), StepLen (1/16th to 4x), Repeat (which also lengthens the step) and Divide (like Repeat but shortens the slice rather than lengthening the step). Groove and StepLen are especially handy for slice sequencing because they free you from needing equal-sized slices cut precisely on gridlines (see Fig. 3 and Web Clip 5).

You can create sequences as long as 128 steps and enter pitches with the mouse or incoming MIDI (step-by-step or in real time). Complete Stack setups (excluding Audio Units plug-in parameters) are saved as presets, which you sequence on Numerology's multitrack timeline or trigger manually from your computer or MIDI keyboard.

Beyond Monophonic

Powerful though the Mono Note sequencer is, you can go even further with discrete sequencing: using separate CV Sequencer modules for gating, pitch and velocity. If you want the gate and pitch sequences locked together — when working with differing slice sizes, for example — it's easiest to start with a Mono Note sequencer and then add a CV VelocitySeq module to generate an asynchronous accent pattern. You might then use the Mono Note's RandJmp lane to introduce some randomness into the sequence. For example, setting the RandJmp slider to 0.50 for a couple of steps causes the next step number after those steps to be selected at random half of the time (see Web Clip 6).

FIG. 4: The Matrix Arpeggiator sequences the arpeggiated notes in the order you specify using a graphical matrix. In the lower bar graph, alternate notes are adjusted to produce a swing groove.

FIG. 4: The Matrix Arpeggiator sequences the arpeggiated notes in the order you specify using a graphical matrix. In the lower bar graph, alternate notes are adjusted to produce a swing groove.

Although step sequencing is Numerology's main function, it has many other tricks up its sleeve. For one, you can apply all the flexibility of its step-sequencing paradigm to arpeggiation with its Matrix Arpeggiator module. That module has 12 pitch rows whose pitches are automatically assigned in ascending order to the currently held notes. Matrix is polyphonic, and, instead of sliders, a note matrix is used to choose which note(s) play at each step (see Fig. 4). An accompanying gate and velocity sequencer offer all the step options previously described for the Mono Note sequencer.

The keyboard module visible at the top of Fig. 4 lets you generate chords with the mouse or incoming MIDI. Most important, the current chord is saved in Stack presets, letting you sequence chords on Numerology's multitrack Timeline (see Web Clip 7).

Your options for step sequencing and arpeggiating sliced audio files range from fast and straightforward solutions like using pre-sliced REX files in Reason to D.I.Y. alternatives as described for Live and Numerology. The latter requires more tweaking and, in the case of Numerology, building your sequencer from its modules. But the results are ample reward for the time spent.


Len Sasso is an associate editor of EM. For an earful, visit his Website, swiftkick.com.

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