Frequency shifting is a great way to add color and motion to almost any percussion sound. For this article, I've used the Bode Frequency Shifter module in Arturia's Moog Modular V2 (MMV) to liven up some fairly bland audio percussion tracks. You'll find the MMV patches described here on the EM Web site.
FIG. 1: The frequency shifter setup for toms uses an envelope follower to trigger a standard ADSR envelope, which is used to modulate the amount of frequency shift. The envelope's release time contols the contour of the modulation.
If you're using the MMV as a plug-in, you'll need to keep the VCA gated on, which you can do by assigning Keyboard Trigger Off as its trigger input and setting its sustain to maximum. You'll also need to cable one of its external inputs (or a mix of both) to the frequency shifter's input and to cable the frequency shifter's Mixt output to a VCA input. The Mixt knob then controls the mixture of upper and lower sidebands you hear; usually, you'll want it fully clockwise or counterclockwise to restrict the output to one set of sidebands. Alternatively, you can use the A and B outputs to process the sidebands separately.
I Get a Kick
A small, slowly varying shift can make each hit of a kick drum sound a bit different, making the whole track come alive. Set the frequency shifter's initial shift close to 0 Hz, and set the scale to 50 Hz. Use the random output of an LFO synced to the host tempo to modulate the amount of shift; settings between 0.25 and 0.50 work well. Tweak the settings, especially the LFO rate, so that the variations in timbre sound natural and the amount of shift doesn't change during individual hits.
You can add some life to a snare drum by using an envelope follower to modulate the amount of shift in a direction opposite to the initial shift. An initial upward shift in the 50 to 100 Hz range with a modulation of -0.20 and a scale of 500 Hz works well. The envelope follower applies the most modulation during the loudest part of the input sound, which results in the least shift during the snare-drum attack. The shift increases as the snare dies out.
You can smooth the modulation by using the envelope follower to trigger a standard ADSR envelope. In any case, the envelope follower's trigger output must actually be used in the patch. Using it as the trigger source for an envelope is one approach.
A similar setup, but with a smaller initial amount and with the modulation in the same direction as the initial shift, works well for toms. Use a very small modulation amount, and tweak the envelope release to taste. Add a little random LFO modulation to sweeten the effect (see Fig. 1).
Cymbals of Excess
Cymbals practically beg to be shifted, and large shifts often work well. A step sequencer or an LFO, with their clocks synced to the host's tempo, make interesting modulation sources. With the step sequencer, use an odd number of steps and alternate positive and negative values. With an LFO, try a fairly fast sine wave, and use an envelope triggered by an envelope follower to fade in the LFO by passing it through one of the mixer's control amplifiers. Also try using both the upper and lower sideband outputs of the frequency shifter panned to opposite sides of the stereo mix.
The processing described here, all of which can be heard in Web Clip 1, is at the subtle end of the range of possibilities. Try extreme shifts, radical modulation by multiple sources, and processing by other DSP effects before or after the frequency shifter. As with all sound design, breaking the rules often yields the most interesting results.
Len Sasso is an associate editor of EM. He can be contacted through his Web site atwww.swiftkick.com.