Exercise B: Modulation
A Bit of Theory
When we modulate a parameter, we should think about the offset of that parameter — its basic setting — and the attenuator applied to the modulation signal before it affects the parameter.
An example...A sine wave LFO emits a full-amplitude signal whose voltage ranges from -5 to +5 (in VCV Rack). When you apply this to the frequency of a VCO, without attenuation, the vibrato spans the entire audible range of frequencies. To create a typical vibrato, we scale down the LFO output so that it falls closer to the range -0.1 to +0.1 volts. An attenuator performs this scaling.
The fluctuating frequency of the VCO that results — the vibrato — sounds roughly symmetrical around the frequency set for the VCO using its FREQ dial. That is the offset frequency. Modulation always acts on a parameter relative to the offset of that parameter.
Often an attenuator is built into a module: it appears as a knob next to the control voltage (CV) input that it scales. Sometimes there is no built-in attenuator. In that case, you can use a simple VCA module to attenuate the CV signal before it reaches the CV input of the target module. There are other modules whose only job is to manipulate a CV signal: by scaling, offsetting, inverting, quantizing, or sampling it.
Start with the “basic patch.” Add an LFO module, and connect (one of its) waveform outputs to the FM input of your VCO. What dial controls the depth of vibrato — in other words, the attenuator?
Once you figure that out, use another LFO to control filter cutoff frequency (wah-wah) or amplitude (tremolo). For those, you need to know which parameter of a module requires input from an LFO. Locate the offset of that parameter and the attenuator for the LFO signal.
One module that can attenuate control voltages — or audio signals, for that matter — is VCA.
It’s straightforward to create a tremolo with full depth. (Our reading on modulation shows a patch for this.) But if you want to have a variable depth of tremolo, you need to use a module that allows you to invert, offset, and scale the control voltage before applying it to the target VCA module. One such module is Dual Attenuverter by Befaco.
- Save your rack to disk as “Exercise B.vcv,” and submit this in Canvas.
This assignment will be graded pass/fail. If it produces sound and implements two of the three main kinds of modulation, you pass. You may ask for help with it during tutorial before submitting it on Thursday night.