Why is the output shorter than the input?

Because a modulated delay line has to be filled before it can output anything, and it needs room on both sides of the sweep so the read position never runs off either end. The source samples consumed by that headroom do not appear in the output, and the report states the percentage.

How deep is a natural vibrato?

Roughly twenty to sixty cents for a singer, which is why fifty is the default. Beyond about a hundred cents the movement stops reading as expression and starts reading as a deliberate effect, which is useful but is a different thing.

Why is linear interpolation used?

Because the read position of a modulated delay rarely lands exactly on a stored sample. Interpolating between the two neighbours produces a smooth value at any position, which is what keeps the pitch movement continuous rather than introducing the graininess a nearest-sample read would create.

Is the reported cent figure the same as the setting?

It is the swing the settings actually produce, recomputed from the modulation depth, the oscillator's frequency and the relationship between an excursion in time and a change in pitch. That is why it is worth checking when the rate is extreme, since the same depth at a higher rate produces a larger swing.

Can I use it to correct a pitch that drifts?

Not directly, because the movement here is a fixed oscillation rather than a correction. Pitch correction is the tool for following and correcting an existing drift, since it measures each note and pulls it back to where it should be.

Vibrato Effect

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Vibrato Effect makes the pitch of a recording rise and fall at a steady rate. It is produced by sweeping a short delay line, so the movement is in the pitch rather than in the level.

What is Vibrato Effect?

Set the speed and the depth in cents, drop a file, and process; the panel reports the settings, the verified swing, and how much shorter the output is.

The controls:

A speed from one to fourteen hertz, in half hertz steps, defaulting to six and a half.
Three presets at five, six and a half and eight hertz, which sit around the range a singer's natural vibrato occupies.
A depth from five to two hundred cents, in five cent steps, defaulting to fifty.
A footer reporting the swing in cents as verified from the modulation depth, the rate, and the percentage by which the output is shorter than the source.

The mechanism is a delay line whose length is modulated by an oscillator, with the output read from an interpolated position between the stored samples. Because the read position moves, the pitch of what comes out rises and falls exactly as the delay shortens and lengthens, and the relationship between the two is defined precisely enough to be worth knowing: the depth in cents translates into a peak delay excursion, and that excursion multiplied by the oscillator's angular frequency gives the maximum fractional rate change, which is the pitch swing. The panel recomputes the swing from the actual modulation parameters and reports it, so the figure is a verification of the implementation rather than a restatement of the setting. Linear interpolation between neighbouring samples is what lets the read position fall between them without introducing a step, which is what keeps the moving pitch smooth rather than grainy. The output is shorter than the input, and that is not an error but the arithmetic of the method: the delay line has to be primed before it can produce output, and its headroom has to be reserved on both sides of the sweep, so a portion of the source is consumed before the first sample comes out. The reported percentage is the honest measure of that cost. Depth is what decides whether the effect is a natural vibrato or a siren: fifty cents is around a quarter tone and reads as expressive singing, while two hundred cents is a full tone and is a stylistic effect rather than a natural one.

What it does not do:

No feedback, so it is a vibrato rather than a chorus or a flanger.
No synchronisation to a tempo.
No independent modulation per channel.
The output is necessarily shorter than the source.
No control of the oscillator shape.
Output is sixteen bit WAV.

Use it to add natural movement to a sustained instrument or a held vocal note, to thicken a part that was recorded too steadily, or as a deliberate effect on synths and guitars. When the movement should be in the level rather than the pitch, the tremolo is the counterpart, and when the aim is to widen or double a part rather than to move its pitch, the chorus and the stereo widener do that. The movement is deliberately periodic rather than natural, which is why it works as an effect rather than as a correction.

How to use Vibrato Effect

Drop an audio file onto the panel.
Set the speed, using a preset near the rate a voice would naturally use.
Set the depth in cents, starting around fifty for a natural feel.
Process the file, check the reported swing and length change, and download the WAV.

When to use Vibrato Effect vs related tools

Vibrato Effect is the tool for pitch movement on a sustained part, which makes it useful on held vocals and on instruments recorded too evenly. Tremolo Effect moves the level rather than the pitch. When the movement should be a filter rather than a pitch, Chorus Effect and Flanger Effect modulate a delay at longer or shorter settings, and Pitch Shift Calculator is where a fixed pitch change is worked out.

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