Tremolo is the modulation of volume.
In Sine Machine, it’s the modulation of individual harmonic volumes.
That sounds simple. But remembering the promise of Fourier — that every sound can be decomposed into a collection of sine waves at different pitches and volumes — it’s clear that harmonic volumes have an enormous impact on what we hear.
So it’s called “Tremolo” because that’s exactly what’s you are controlling, but the myriad effects that can result might remind you of other sounds from your favorite synths.
Filter Modulation
Removing volume from the higher partials basically lowpasses the sound.
Modulating this volume with tremolo = filter modulation!
Timbre Morphing
Modulating only the odds or evens are a way to drastically morph between timbres in a rhythmic way.
Trem Types
Sharpness
Increasing sharpness makes the tremolo more dramatic, gives it more attack.
For triangle and ramp shapes, turning up the sharpness increases the exponential-ness of the attack and decay, making it very pulse-y and…. sharp. Turning down the sharpness produces more of a linear sound (which is what most synthesizer and effect lfos default to).
For the square tremolo, the volumes are either full on or full off (at full depth). With sharpness halfway, the note is on for 50% of the time, off for 50% of the time. Increasing sharpness turns them off for a larger percentage of the time. Decreasing sharpness keeps them on for a larger percentage of the time.
For the random trem, sharpness controls the amount of transition between the random values. At full sharpness, the new values will instantly blink on. With sharpness all the way down, it will be a linear transition.