Expressive Control

Jul 1, 2006 12:00 PM, By Jim Aikin

           

Controlling more than one parameter from a single MIDI Control Change message is an excellent way to add expression to your synth sounds. In “Square One: The Matrix” (see the June 2006 issue of EM), I explained matrix modulation, the primary tool you would use to set up that type of control. In this column, I will discuss some of the musical applications of matrix modulation. I'll assume you have a synth equipped with a modulation matrix and understand how its features work.

FIG. 1: The modulation matrix in VirSyn TERA 3 provides two banks of ten routings each. A MIDI Mod Wheel can be applied to numerous destinations in different amounts.

The 8-bar filter swell has become a cliché of electronic music: as a rhythmic synth riff loops, the filter gradually opens until the synth dominates the mix, and then closes down again so that the riff recedes. To give this technique a fresh spin, try adding overdrive distortion as the filter opens. Overdrive increases the amplitude of the signal, so you may need to use the same modulation source to slightly reduce the synth's output level.

Controller Scaling

To do that, you need to use controller scaling and controller inversion, both of which you can do using the amount parameter in the modulation matrix. When the amount of modulation is small, the destination parameter changes only a little in response to a big change in the incoming data. If the amount is less than zero, the amount of modulation is inverted. When it's inverted, raising the controller value (by pushing a slider up, for instance) lowers the parameter and vice versa.

Some synths, such as VirSyn Tera 3, which I've used for this column's audio examples, use multiplication rather than addition to control modulation amount (see Fig. 1). In that case, an amount of less than one inverts the modulation.

In addition to opening the filter, you can add a tempo-synced delay line with a wet/dry mix of 40 percent or so. That is especially effective with a ping-pong delay algorithm, which will bounce the synth riff around in the stereo field. You can also blend in a suboctave oscillator (see Web Clip 1).

Envelope Shaping

Check whether your synth allows envelope segment times (attack, decay, release, and others) to be chosen individually as modulation destinations. If so, you can tighten up a sound by decreasing the attack and release times together. You can start with a gentle sound that has short to medium envelope times (100 ms to 250 ms) and pull both times back to zero by moving your MIDI slider up. Web Clip 1 uses this technique.

Another way to add aggression is to increase the depth of envelope modulation. Try using a second envelope to modulate the frequency of a synced oscillator, as heard in Web Clip 2. Use only a small amount of envelope to start with, and add more while also shifting other parameters. In Web Clip 2, an LFO modulates panning, and its depth and rate both increase as the mod wheel is pushed up.

If you're using the mod wheel to add vibrato, you can also lengthen the amplitude envelope release time using the same MIDI message. That will have no effect on the envelope if the mod wheel is pushed up and pulled back in the middle of the note, but it will allow you to add a long, fading vibrato tail to the end of a phrase. (Try increasing the reverb wet/dry mix at the same time.)

Morphology

Many synths offer numerous ways to change tone color, so look closely at the destinations available in your modulation matrix. Ultimately, this technique is a form of patch morphing, which several hardware and software synths also have. With morphing, one patch transforms smoothly into another; instead of defining several modulation routings separately, you define and store the “start” and “end” patches separately, and then assign a single MIDI modulation source to the morph parameter.

A morph can include any or all of the voicing parameters that have a continuous range of values, but switchable parameters (such as an oscillator's waveform selector) usually aren't morphable. That is because morphing them would cause abrupt and possibly jarring changes in the sound. If, however, the amplitude levels of the oscillators are controllable, you can create the effect of changing waveforms during a morph by crossfading from one oscillator to another.

Jim Aikin writes about music technology and plays electric cello. Visit his Web site at www.musicwords.net.