Complete Guide The Vibrato Audio Modulation Effect

Vibrato is a popular and powerful musical technique implemented naturally by singers and available to other acoustic instruments, and it's also available electrically as an audio effect.

What is the vibrato effect in audio? Vibrato is a fast but slight up-and-down variation in pitch. Vibrato is used in signing and in instruments to add character and improve tone. The vibrato audio effect alters an audio signal's pitch by essentially modulating the delay time of a delay circuit.

In this article, we'll primarily discuss vibrato as an audio effect and consider its origins as an acoustic pitch modulation technique. To further our understanding, we'll also consider specific vibrato effects units and how they work.

What Is The Vibrato Effect?

The vibrato effect is a slight but audible modulation in the pitch of a sound or audio signal.

This “vibrating” effect adds expression and character to musical notes without extending to adjacent notes, meaning that, generally speaking, the vibrato effect will modulate within a range of ± 100 cents (± 1 semitone) of the intended note.

Vibrato is largely determined by two factors (which we'll get to in greater detail in the later section titled Vibrato Parameters):

The amount of pitch variation, or “depth.”
The speed at which the vibrato happens, or “rate.”

Musical pitch is a perceptual property of sound that allows listeners to qualify different sounds as being higher or lower in terms of musical notation. This auditory sensation allows us to relate the positions of different notes within the context of a musical melody.

Vibrato can be achieved in several different ways, and we’ll discuss the acoustic and electrical methods in this article. We’ll pay special attention to electrical vibrato as this is the modulation audio effect we’re most concerned about within this particular article.

The vibrato effect, in audio, aims to mimic acoustic vibrato by effectively modulating the perceived pitch of the audio signal in a cyclical fashion.

Vibrato units, then, are responsible for increasing and decreasing (modulating) the signal's pitch within a defined range about the resting pitch of the signal itself.

More technically, the vibrato effect is a phase-shift modulation effect centred around a delay circuit and a low-frequency oscillator (LFO) that modulates the delay time of that delay circuit.

An LFO is an electrical oscillator with a frequency below the audible range of human hearing (below 20 Hz). Typical vibrato LFO frequencies are below 10 Hz though they may certainly be set above this rate. The range of available LFO frequencies depends on the particular tremolo unit.

It’s the modulation of the delay line's delay time that causes the pitch variation.

As the delay time is shortened, the delayed signal wave is experiencing a slight amount of time compression. This time compression shortens the waveform, thereby increasing the frequency (and pitch) of the waveform.

The pitch variation or vibrato intensity is largely determined by the amplitude of the LFO, while the frequency of the LFO determines the rate or speed of the vibrato effect.

A Note On Acoustic Vibrato

This article is largely focused on the vibrato audio effect and, therefore, the electrical side of vibrato. However, to improve our understanding, we should consider instances of natural/acoustic vibrato. After all, the electrical effect often aims to emulate the original/natural acoustic vibrato (though it can certainly be pushed further).

Acoustic vibrato is perhaps most popular in vocal performances, whereby pitch variations can be produced by manipulating the larynx.

In Western music singing, the extent of vibrato is generally less than a semitone (100 cents) to either side of the note's pitch. Otherwise, the pitch variation would be considered a trill or, at the very least, a change in the sung note.

Vibrato can be achieved in woodwind instruments by modulating the airflow into the instruments. This is also the case with the pipes of organs.

Vibrato can be achieved in stringed instruments in a variety of ways. Bending the string by rapidly moving a finger pressing a string against the fingerboard is one way. Another way is by using a “tremolo arm” or “whammy bar” common to electric guitars. Any time we can make slight variations in a string's tension or length, we can produce vibrato.

Vibrato can be achieved in brass instruments by repeatedly and rapidly altering the embouchure.

The Vibrato Circuit Design

Vibrato audio effect units are electrical by nature, so it’s important to understand the basics of their circuits. Note that we’ll be focusing on analog vibrato circuit signal flow in the section. However, the same ideas apply to digital vibrato units and the programmings that run vibrato software plugins.

In the earlier sections of this article, we discussed how the vibrato effect is centred around a delay circuit and a low-frequency oscillator (LFO). This is also true of some other phase-shifting modulation effects such as chorus and flanger.

To be more specific, the vibrato circuit achieves the vibrato effect with a delay path that has its delay time modulated by an LFO.

A simplified diagram of an analog vibrato circuit signal flow would look like this:

Note that, unlike the aforementioned chorus and flanger effects, the vibrato circuit has no dry/direct line from input to output. The entire signal is passed through the delay circuit.

There is also no feedback loop in the delay circuit so as to avoid any repetition in the output signal.

So we know what the vibrato effect does. Now let’s consider how it does it.

If you’ve ever adjusted the delay time of an activated delay unit/plugin, you’ve heard how a delay effect can alter the pitch.

This happens because, as the delay time is increased, the signal is effectively time-stretched, lowering its frequency content and dropping its perceived pitch. Conversely, as the delay time decreases, the signal is effectively time-compressed, raising its frequency content and its perceived pitch.

The amount of delay time is modulated via a low-frequency oscillator (LFO). This causes stretching and compression in the signal waveform and, therefore, variations in the signal's frequency/harmonic content and perceived pitch.

Imagine modulating the delay time back and forth very quickly but subtly. This is effectively what an LFO does to produce the vibrato effect.

Digital vibrato pedals emulate this same basic design with digital delay and DSP (digital signal processing). Vibrato plugins use coding to achieve similar results. Note that these vibrato units have a much higher potential for added functionality as they are not subject to analog limitations (particularly in the delay line).

Vibrato Vs. Tremolo

This section is aimed at the guitarists that may be confused, for I was once one of them myself. Tremolo is not vibrato and vibrato is not tremolo!

Tremolo is defined as the audible modulation of a signal’s amplitude. Vibrato, as we’ve discussed, is the audible modulation of a signal’s perceived pitch.

Both effects can be considered “modulation effects” as both effects have their primary modulated parameter (pitch for vibrato and amplitude for tremolo) modulated by a sort of low-frequency oscillator.

So then, the “vibrato” effect built into some guitar amplifiers (the one that modulates the volume of the output signal) is, in reality, the effect of tremolo.

Similarly, the “tremolo arm” or whammy bar of a guitar does not introduce tremolo. Rather, it offers manual pitch variation that resembles the effect of vibrato.

The Fender Tone Master Deluxe Reverb is but one example of an amplifier with a “vibrato” (tremolo) effect.

The labelling of tremolo and vibrato can become tricky in the world of guitar. It’s important, then, to not only know the true definitions of the two effects but also that you’ll likely run into improperly labelled units during your lifetime.

The vibrato vocal technique is sometimes called tremolo if the pitch variations are wide and/or slow. This can also lead to confusion between the two terms. Note that, in this case, tremolo is simply a slower form of vibrato, which is a more common term in singing.

Vibrato Vs. Pitch-Shifting

Though vibrato and pitch-shifting effects both act to alter their input audio signals' pitch, they are not the same.

As we've discussed, vibrato is an audible modulation of a signal/sound's perceived pitch. Vibrato is typically achieved as variations from a defined pitch. They work with a delay circuit and an LFO (or other control voltage) that modulates the delay time of the delay circuit.

Pitch-shifting effects (which are all digital) work differently. They sample the signal and move its frequency content to a new “note.”

The easiest way to achieve pitch-shifting is by speeding up or slowing down audio. This pitch-shifting is a by-product of time-shifting and is often referred to as “pitch controlling.”

As the name suggests, pitch-shifting works by altering the input signal's pitch and outputting a signal with a different musical note. It does so via electrical means, bringing objectivity to the perceived nature of the musical pitch.

Vibrato Vs. Frequency Modulation

By modulating an audio signal's pitch, the vibrato effect effectively varies the frequency content of that signal.

However, vibrato is not the same as frequency modulation, which is used as a basis for audio synthesis, radio transmission and other audio applications.

Frequency modulation uses a modulator signal (similar to the LFO of the vibrato effect only much faster) to directly alter a carrier signal's frequency. Remember that the “modulator” of a vibrato circuit controls the delay time of a delay circuit.

By modulating the frequency of a carrier signal, FM can be used in the following ways:

FM synthesis to create synthesized waveforms (the carrier wave is modulated by a modulator wave, typically in the audible range of frequencies).
FM radio transmission (where the carrier signal is in the very high frequency “VHF” band).

Note that, at these modulator frequencies, we cannot perceive any change in “pitch” within the output signal.

Here is a simple illustration of how frequency modulation works with sine waves:

Vibrato Parameters

Now that we comprehend what vibrato is and how vibrato effect units work, let's look at the various parameters that will effectively detail the performance of the vibrato effect.

The vibrato effect is relatively simple, and so its parameters are few.

That being said, vibrato effect units will often have many (if not all) of the following controls:

Depth
Speed/Rate
Tap Tempo/Sync Option
Rise Time/Ramp

Depth

The depth parameter of a vibrato effect unit affects the amplitude of the LFO. This narrows or widens the modulation range of the delay circuit's delay time and, therefore, the amount of pitch variation the effect will produce.

Speed/Rate

The speed or rate parameter of a vibrato effect unit controls the frequency of the LFO and, therefore, the speed of the perceived pitch variation.

Tap Tempo/Sync Option

Some vibrato units/plugins will allow users the option of synchronizing the effect to the tempo of a project/song. This parameter will switch the speed/rate function (typically defined in Hertz or cycles per second) to note length values (quarter notes, triplet quarter notes, dotted eighth notes, etc.).

Rise Time/Ramp

The rise time or ramp parameter controls the attack time of the LFO's amplitude envelope. It alters the initial onset time of the vibrato effect once the unit/plugin is engaged by ramping up the level of the LFO.

Vibrato Effect Unit/Plugin Examples

Before we wrap things up, it’s always a great idea to consider some examples. Let’s look at 4 different vibrato units to help solidify our understanding of this modulation effect.

In this section, we’ll discuss:

500 series vibrato unit: JHS Emperor 500
19″ rack mount vibrato unit: Matchless TV-1
Vibrato effect pedal: Boss VB-2W Waza Craft
Vibrato plugin: MeldaProduction MVibratoMB

JHS Emperor 500

The JHS Emperor 500 is a 500 series analog vibrato/chorus module with a real 3207 BBD (bucket-brigade device) chipset.

In addition to the 5 control knobs (Volume, Mix, Tone, Speed, and Depth), the Emperor includes switches for the following:

Bypass: turns the unit on and off
Chorus/Vibrato: switches between the two effects/modes.
Waveform: changes the LFO waveform between sine, square and triangle waves.
Expression/Tap: changes how the unit reads the 1/4″ tap tempo/expression input.

The 1/4″ tap tempo/expression input allows for increased control over the speed parameter of the vibrato (and chorus) effects.

Matchless TV-1

The Matchless TV-1 is a rack-mounted vibrato/tremolo effects unit. It's been discontinued but is still worth mentioning.

This analog unit utilizes several tubes in its design and provides a wonderful vibrato (and tremolo) effect. In terms of controls, the unit is pretty straightforward.

First, the TV-1 has a single mono input with input level control and a stereo output (left and right mono) with independent output level control.

There are switches for the following:

Regenerate/Normal: introduces feedback into the modulation circuit (regenerate) or removes feedback from the modulation circuit (normal).
Tremolo/Vibrato: switches between the two effects/modes.
On/Off: turns the unit on and off.

The speed and depth controls are what we'd expect of a vibrato effect unit.

Boss VB-2W Waza Craft

The Boss VB-2W Waza Craft is a superb vibrato effect pedal.

The VB-2W Waza Craft is a remake of the original 1982 Boss VB-2 vibrato, which was well ahead of its time. Just like the original, the VB-2W utilizes an all-analog BBD design that gives a superb vibrato sound.

This pedal offers a Standard mode that reproduces the sound of the original and a Custom mode that emphasizes modulation.

The pedal can be set to latch, unlatch or bypass mode via a rotary knob. Latch turns the effect on or off each time you press the footpad. Unlatch turns the effect on only when the footpad is held down. Bypass mode is like Latch mode, only that the pedal sends the input signal directly to the output when bypassed.

The Boss Waza Craft VB-2W features the basic vibrato parameter controls with the other 3 knobs:

Rate knob: adjusts the modulation speed.
Depth knob: adjusts the modulation depth (pitch variation).
Rise Time knob: adjusts the time it takes for the full vibrato effect to happen.

An external expression pedal can be connected to control the depth of the effect in real-time.

MeldaProduction MVibratoMB

The MeldaProduction MVibratoMB is a multiband vibrato plugin.

The MVibratoMB allows up to 6 fully customizable and independent frequency bands that can each have their own vibrato settings.

The modulating oscillator can be shaped in many different ways to produce truly unique vibrato movement. Each band can be modulated by up to 4 global modulators (LFO, envelope follower, MIDI/audio triggered envelope, pitch detector, or a combination of several).

This plugin can handle mono and stereo processing along with up to 8 channels of surround processing.

Syncing with the DAW is made easy, and the plugin even offers a randomizer option to produce completely new settings at the press of a button.

Though we've covered the basics, there's a lot more to this deeply powerful vibrato plugin.

Call To Action!

Experiment with vibrato effects, whether they be plugins or hardware. Listen critically to how the modulation changes the sound over time. Adjust the parameters to get a sense of the extremes.

Find and listen to songs that utilize the vibrato effect to really internalize its sound and how it's used.