Dance: Sideband Morphing

December 13, 2011
By Francis Prève

One of the cooler tricks for creating morphing leads for buildups, breakdowns, and transforming riffs over the course of a track is the application of sidebands. Sidebands are additional frequencies that aren’t necessarily related to the harmonic spectrum of the original tone—though with careful tuning, they can be. Anytime an LFO rate exceeds 20Hz and enters the audio range, sidebands are generated.

One common example is ring modulation, which creates two sidebands that are the sum and difference of the original tone (the carrier) and the ring mod frequency. Another classic is FM, which applies audio-rate modulation to the pitch of the carrier oscillator. When the modulator is tuned to a specific harmonic, the results are musical. When the modulator is tuned to a non-integer frequency, the results are clangorous. Some of LFOs can exceed “low” frequencies and enter the audio range. Reason’s Subtractor includes this feature, so we’ll use that for our examples.
Pitch Modulation (FM)
Start with an initialized patch, turn Velocity-to-Filter off, increase the volume envelope sustain to maximum, and open the lowpass filter cutoff all the way. Next, set LFO1’s amount to maximum (so you can hear the results) and its unsynced rate to zero. Play a note and slowly raise the LFO rate (either manually or via automation) until you hear the vibrato dissolve into a mess of additional pitches that shift as you turn the knob. Then reduce the LFO rate and listen to the sound revert to vibrato.
Filter Modulation
Modulating the filter cutoff is another cool way to add spice to a lead or breakdown. The effect is most pronounced when the cutoff is set to about 30-50% and the resonance set at a value greater than 30%. Again, start with the initialized patch above, but set the LFO destination to filter frequency (left). Then, set filter cutoff and resonance to about 40% each (right) and repeat the experiment.
Amplitude Modulation
Technically, this is similar to ring mod, as both effects rely on audio-rate modulation of an amplifier, with ring mod eliminating the carrier tone, unless a wet/dry knob is present. Since Subtractor doesn’t provide amplitude modulation on LFO1, we’ll set the LFO destination to “Mix” (left). Begin with the initialized patch once again, and keep oscillator 2 turned off. Next, turn the Osc Mix knob fully counterclockwise so that the Mix modulation only affects the volume of oscillator 1 (right). Now, repeat the LFO experiment described above.

Those are three common approaches, but almost any synth parameter destination will provide interesting results. If your synth allows, try modulating the pulse width or waveform instead. Plus, panning combines elements of amplitude modulation but with a stereo flair. Be sure to try different LFO waveforms as well.

11-2011 Dance: Sideband Morphing by KeyboardMag
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