Reset: Many LFOs have a reset input that forces the LFO’s waveform cycle to reset. But some can smoothly morph between waveforms where more interesting shapes can be accessed. Often they consist of the classic waveforms - sine, triangle, sawtooth/ramp, square. Waveform: LFOs have multiple waveforms to choose from. If it was an audio oscillator, the frequency would be the pitch of the sound. Same for the amplitude of a sound going through a VCA (this is how we make tremolo sounds).įrequency: The frequency is the number of waveform cycles per second. It can also be patched into the cutoff frequency input of a filter, changing the cutoff frequency in the same manner at the oscillator (this is how we make sweeping sounds). This continuous low and slow AC signal can be used to modulate parameters of other modules.įor instance, the output of a LFO can be patched to the pitch input of an oscillator making the oscillator change pitch at the frequency, waveform, and amplitude of that LFO (this is how we make vibrato sounds). They are oscillators with a frequency range that can go much lower than the range of human hearing which is 20Hz - 20kHz (some LFOs go well into audio rate, and yes, even at control rate one will hear a click with each period of the waveform). Low frequency oscillators are exactly what they sound like.
The modules that change voltage in the realm of control rate are those we’ll focus on today.
Last time when we spoke about VCAs, we learned that modulation can occur at control rate and at audio rate. How do we breathe life into our patch and make it both organic and musical? The question now is how to make these changes in sound happen in specific and precise timings, shapes, levels, and movements. At this point, we can make a sound that has the potential to change pitch, texture, timbre, and loudness.
Over the last few posts, we’ve talked about all the basic modules that exist within the audio path of a synthesizer patch: oscillators, filters & VCAs. Basic Synth 4: LFOs, Envelopes, and Random Voltage
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