What is the difference between tremolo and vibrato?

Tremolo varies the level and vibrato varies the pitch. The two are often confused because amplifier makers have historically labelled their pitch modulation as tremolo, but the effects are distinct and are produced by entirely different means: one scales the signal, the other moves a delay line.

Why does the modulation use a raised cosine?

Because it has no corners, so the level reaches the bottom of each cycle and leaves it smoothly. A linear or switched modulation would introduce a kink in the waveform at every half cycle, which is audible as a click or as an unnatural regularity.

Which rate sounds like a classic amplifier tremolo?

Around four to five hertz. Below about two it reads as a slow swell rather than as a tremolo, and above eight it becomes a flutter. The presets span that range, and the useful settings are usually toward the middle of it.

Does tremolo work on a full mix?

It can, and a very shallow setting across a mix adds a subtle sense of movement. Deeper settings are better kept to individual parts, since modulating everything at once tends to read as a wobble on the whole recording rather than as an effect on anything in particular.

Can I make it follow the tempo?

Not automatically, since the rate is in hertz rather than note divisions. Working out the tempo first with the BPM calculator and then choosing a rate that corresponds to a subdivision is the way to line it up with the music.

Tremolo Effect

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Tremolo Effect makes the level rise and fall at a steady rate. It is a single dimension of movement applied to a sound, with the shape fixed and only the speed and amount to choose.

What is Tremolo Effect?

Set the speed and the depth, drop a file, and process; the level swings between the original and a reduced value at the chosen rate.

The controls:

A speed from half a hertz to twelve, in half hertz steps, defaulting to four.
Four presets at two, four, six and eight hertz, covering the range from a slow swell to a flutter.
A depth from nothing to everything, defaulting to fifty percent, which is how far the level drops at the bottom of each cycle.

The modulation is a raised cosine, which means the gain follows a smooth curve between one and one minus the depth rather than moving linearly or switching. The choice of shape matters more than it might appear. A raised cosine has no corners, so the level arrives at the bottom of each cycle and leaves it gradually, which is what keeps the effect from sounding mechanical or adding a click. The oscillation never reaches zero unless the depth is at its maximum and the shape is smooth there as well, so nothing is ever switched off. Because the modulation is applied to the amplitude of the signal rather than to a delay line, the pitch and the frequency content are entirely untouched. That is what separates a tremolo from a vibrato, which modulates pitch instead, and from a chorus or flanger, which modulate a delay and therefore produce either doubling or comb filtering. The rate is the character: a couple of hertz reads as a slow swell, around five is the classic guitar amplifier tremolo, and above about eight the effect becomes a fast flutter that can add a nervous quality to a sustained part. Depth is the amount, and moderate settings are more useful than extreme ones on material that already has movement of its own. At zero depth the gain is one everywhere, so the signal passes through unchanged.

What it does not do:

Only amplitude modulation, with no pitch or filter movement.
No synchronisation to a tempo, so the rate has to be chosen against the music by ear.
No control over the modulation shape.
No stereo offset between the channels.
No synchronisation with other effects.
Output is sixteen bit WAV.

Use it to add movement to a sustained part that would otherwise be static: a held organ chord, a synth pad, a clean guitar arpeggio or a rhodes. When the modulation should move the pitch rather than the level, the vibrato is the counterpart, and when the movement should come from a filter sweep driven by the material itself, the auto-wah responds to the playing rather than to an oscillator. Tremolo is also one of the few effects that can be applied to a whole recording without drawing attention to itself, provided the depth stays shallow: at a few per cent the sense of movement is felt rather than heard, which is the intended use for a setting this subtle. The rate is what decides how the movement reads, and the useful test is to listen to whether it settles into the music or fights it; a rate that lands between the beats is harder to ignore than one that sits on them.

How to use Tremolo Effect

Drop an audio file onto the panel.
Set the speed, using a preset if a familiar tremolo rate is what you want.
Set the depth for how much the level should drop at the bottom of each cycle.
Process the file and listen for whether the rate sits with the music.

When to use Tremolo Effect vs related tools

Tremolo Effect is the tool for level movement on a sustained part, which is why it suits held chords and pads. Vibrato Effect moves the pitch instead, which is the other half of the same idea. Auto-Wah sweeps a filter according to what is played rather than at a fixed rate, and Chorus Effect adds movement by doubling the part rather than by modulating its level.

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