tremolo

Tremolo is an effect that makes a sound's volume pulse in a regular rhythm. Think of a fluorescent light flickering brighter and dimmer over and over. The sound switches on and off very quickly in a repeating pattern, making it seem like it's trembling — and the key point is that what's trembling here is the volume.

A similarly named effect, vibrato, trembles something different. Vibrato is a subtle wavering in pitch, while tremolo is a wavering in volume. Both effects commonly show up as simple on/off toggles in old guitar amps, synthesizers, and even today's browser-based instrument apps.

The usefulness of this effect is that the device automatically raises and lowers the volume at a steady rate, without the performer having to manually pump the volume with their hand or a pedal. Because of this, it's often used to add tension to calm background sounds or bring life to a monotonous tone.

The article introduces "Air Theremin," a browser-based instrument that you play by having a webcam track your hand movements, explaining that "you can toggle vibrato, tremolo, and echo effects on and off." Here, tremolo is an effect that pulses volume, not pitch, so it shouldn't be confused with vibrato, which wavers pitch by shaking your hand.

1. Go to a web-based theremin-style instrument page and pick a waveform you like (sine, triangle, etc.).
2. Turn on the tremolo effect from the top bar or options menu.
3. Try holding the same note steadily with your hand or mouse.
4. Compare the sound with tremolo on versus off, and listen for whether the volume rises and falls in a regular pattern.
5. Now turn on only vibrato and hold the same note, so you can directly hear the difference between tremolo (volume wavering) and vibrato (pitch wavering).