Modulation Effects – Flanger, Phaser, Tremolo & Chorus Pedal

In electronics and telecommunications, modulation is defined as a process in which one or more properties of a periodic waveform is altered based on the information to be transmitted.The periodic waveform that gets altered is known as the carrier signal. When we talk of guitar modulation effects, it is not exactly the same process as defined above, in the true electrical sense. So let us understand what modulation in audio effects parlance means.

What is modulation in audio?

In relation to the effects, the term “modulate” implies a change over time in amplitude, frequency, phase or time of the signal from your electric or bass guitar. The purpose is to add intensity, depth and layers to the original guitar signal without any distortion.

The difference with the usual modulation process lies in the fact that 

  • There we use the information signal like sound to modulate the periodic carrier waveform.
  • In effects, we use a periodic Low Frequency Oscillator (LFO) signal to modulate our guitar signal. This means that some parameter of the actual guitar sound gets modulated instead of a periodic carrier signal, based on the amplitude, frequency and shape of the LFO waveform. Frequency of LFO is kept below 20Hz so that it is not in the audible range.

Modulation effects can make your tone wobble, chop, spin or vibrate adding space and dimension in the process. Their sounds can range from mere pulsing of the guitar volume, as in the case of a tremolo to complex swirling and modulation of frequencies in your guitar signal to very dramatic effects.

In the field of signal processing, modulation is carried out by any one or combination of the following processes:

  1. 1
    Variation of signal strength over time
  2. 2
    Variation in pitch
  3. 3
    Mixing the dry (original) signal with a wet signal (obtained by modulating dry signal with other waveform)
  4. 4
    Splitting of original signal into two parts.Then altering one signal and mixing it back with the unaltered signal.

The major waveform modulation effects are:

  1. 1
    Flanger - Time modulation + Mixing with the dry signal.
  2. 2
    Chorus - Frequency modulation + Mixing with dry signal
  3. 3
    Vibrato - Frequency Modulation
  4. 4
    Phaser - Phase modulation + Mixing with dry signal
  5. 5
    Tremolo - Amplitude Modulation
  6. 6
    Rotary Speaker Emulation.

In modern times, the electronic circuitry used to create these effects can range from being fairly basic to very complex. Many of these effects can be built through analog or digital technology. It is generally accepted that analog effects produce warm and organic sounds while digital technology can generate powerful and dramatic effects. 

Let us now look at each of these effects in detail and go through their underlying principles, impacts, control parameters and important aspects to consider before buying these effects.

Phasers

The early phaser pedals were developed to recreate the sound of rotating organ speakers.  These pedals gained popularity in the 1970's and have grown in prominence ever since and have become one of the most recognizable effects. Some of the popular phaser pedals are - MXR Phase 90, EHX Nano Small Stone, TC Electronic Helix, Boss PH-3 Phase Shifter and MXR EVH 90

What Does A Phaser Do?

Phasers or phase shifters work by splitting the guitar signal into two identical copies. The first copy passes through the pedal without any processing and is referred to as the dry signal. The second copy or leg is shifted out of phase by an angle with respect to the first leg. This phase shifting is done throughout the frequency spectrum and the output is called the wet signal. Many stages of voltage controlled all pass filters are used for the shifting process that keeps amplitude of the leg the same and just shifts the phase..

Phaser_feedback

The two signals are then blended at the depth and speed dictated by the pedal control settings to create the phase effect. Blending results in constructive and destructive interference, whereby the out of phase frequencies are cancelled, resulting in characteristic notches of the phasers.

The number of notches depends on the number of stages, as discussed in detail in the next section. Notch filter causes attenuation of a very narrow band of frequencies, while allowing others to pass through, looking like a curved V shape on a frequency domain graph. The center frequency of the notch is the deepest point with maximum attenuation. 

Phaser_response

Frequency response of an 8-stage phaser with no feedback, dry/wet ratio: 50/50%

These center frequencies are then modulated up and down, creating a feeling of automatically moving tone control. The magnitude of phase shift varies with frequency and changes periodically, resulting in frequency sweep type of effect. This is known as phase sweep.

Stages & Controls

The wet signal is passed through a number of all pass filter stages to enhance the effect. More the number of stages, more pronounced is the phase effect. Analog phasers may have 4, 6, 8 or 12 stages while digital effects may go upto 32 or evenmore. 

A Phaser with 12 stages will produce 6 notches or peaks in the frequency spectrum. As a rule, n stage phasers will produce n/2 notches. More stages may not always mean better, but create necessarily different effects.  You can see how all pass filters and phasers work and effect of stages in the below video.

The controls on the phasers may accordingly vary from the very basic ones to very complex. A four stage unit may just have the speed control, while the models with eight to twelve stages may have multiple knobs and switches. The common controls on the phase effects used to modulate wet signals are:

  1. 1
    Speed or Rate: Rate of periodic phase sweep. This decides how fast or slow the stages cycle the signal from being in-phase to out-of-phase and vice versa. With a slow speed setting, an in-phase signal will go out-of-phase and come back in-phase in a slow swirly effect. Increasing the speed setting will create a pulsing effect as the signal rapidly goes in and out of phase.
  2. 2
    Intensity, Depth, Mix or Amount: The magnitude ratio of original and phase shifted signal. Depth can be increased by mixing more of the phase shifted or wet signal to the dry one or by use of a larger LFO signal. Depth defines how far the signal goes out of phase. Low depth setting creates a very subtle effect, as signal moves slightly out-of-phase and back in, while cranking the depth results in huge variance in phase. 
  3. 3
    Shape: Shape of waveform to periodically modulate the phase sweep. Common choices are Sine, Triangle, Square etc.
  4. 4
    Feedback, Resonance or Color: In some of the phasers, the output is fed back to the input to further intensify the effect. The intensification happens due to resonance, which emphasizes frequencies between the notches and results in peaks and troughs in an unusual way. Some of the phaser pedals have a “Color” knob to control the amount of feedback added into the circuit.   
Phaser_response_with_feedback

Frequency response of an 8-stage phaser with 50% feedback, dry/wet ratio: 50/50%

Sounds Of A Phaser

The sound of a phaser can vary from a very subtle, watery burble to a sweeping, dramatic vibrato like oscillations. That is, it sounds equally great on clean and dirty tones.

The video below features the song "Atomic Punk" from Eddie Van Halen. The iconic tone at the intro to the song summarizes the effect very nicely.

Most players prefer to lightly add color to their tone by using it with a little restraint in the former manner. Subtle phasing can add a lot of life to your otherwise dull and lifeless clean tone. 

Phaser is a versatile modulation pedal that adds texture and motion to overdriven tones and deepens a clean tone. It can bring in a very subtle chewy texture and increased depth even at very slow speed and low depth settings. A deep setting on the phaser can make a clean tone sound really amazing.

Slow speed setting causes gradual increase and decrease in resonance and sounds like an EQ filter moving up and down the frequencies. This is due to cancellation of some frequencies and addition to the other ones. At higher speed setting, instead of a sweeping sound like in the previous case, you get a pulsing effect. 

Use of phaser adds a lot of character to the standard lead tone giving you more expression in the same way as the Wah pedal does. Increasing the feedback, adds more resonance to the sweep, making it more pronounced. 

It’s position in the signal chain has a big impact on the overall sonic effect, specifically in relation to the overdrive and the fuzz pedals.

Some Famous Guitar Songs With Phasers

There are many songs with exemplary use of phasers that act as a major source of inspiration for aspiring guitar players and experts alike. The following list of selected songs will provide you the feel of the different options you have.

  1. 1
    Eruption - Van Halen
  2. 2
    Paranoid Android - Radiohead
  3. 3
    Kashmir - Led Zeppelin (Drums)
  4. 4
    Little Wing - Jimi Hendrix
  5. 5
    Shattered - Rolling Stones
  6. 6
    Lost in the Supermarket - Clash
  7. 7
    Smashing Pumpkins - Soma
  8. 8
    Ain’t talkin bout love - Van Halen

Things to Consider Before Buying A Phaser Pedal

  1. 1
    Where to use the phase effect - Some of the common areas to consider using the phasers are (a) To enrich and deepen your solos - like using a boost pedal without any actual gain.This allows even the few notes to create a lot of emotions. (b) Melodic verse fills - Phaser at a slow speed thickens the sound which is a very subtle and barely noticeable effect but colorful. This makes a few notes or short melodies to count for more. Many players have used it to give a flavour to verse melodies without relying on heavy choruses. (c) Chord swells -  Swirling sounds from the extremes of the phase effect makes the ringing chords to have more sustain. This phenomenon is known as chord swell. Chord swells sounds best on slower songs than fast paced. As a matter of fact, phasers in general work best for held notes and uncomplicated riffs rather than note heavy or complex leads. 
  2. 2
    How many stages - Each of the stages in the phaser will add a notch and a peak in the frequency response, giving more complex overtones. As pointed out earlier, more stages does not necessarily mean better, but will create different effects.
  3. 3
    Digital or Analog - As is the case with all sound effects, analog phasers provide vintage, warm and rich sound, while digital technologies have the obvious advantage of versatility and infinite possibilities. Any digital pedal also gives you an option of storing many presets, which can be used, during live performances. In the case of a phaser pedal particularly, having digital technology may allow you to have more stages, if that is what you are looking for.
  4. 4
    Adjustability & Ease of Use - Depending on the variation of phaser sound you are looking for and your familiarity with the effect, you can choose one with very basic controls or go in for a more complex option. It is however recommended to have Speed, Depth and Resonance controls as a bare minimum.
  5. 5
    Sound Performance - this is usually the most critical factor that governs the selection of any particular phaser. Each pedal will give different phasing options and will color the sound differently. It is always recommended to either try them in person or to listen to some of their demo videos online.
  6. 6
    Size - Depending on the free space available on your pedalboard, you can select the phaser that best fits in there. However, smaller size may also mean less features and capabilities. You may need to make a choice based on your playing styles, expertise and expectations from the pedal.
  7. 7
    Inputs & Outputs - Some of the phasers come with stereo inputs and outputs, which can be used for connecting any stereo instrument or for splitting the signals. You may also want to connect an expression pedal to your phaser to control some of the parameters with your feet.
  8. 8
    Position In signal chain - It is always best to put the phasers towards the end of the signal chain. These should be placed after all the other effects except the ambient ones like delay & reverb, so that effect is applied to everything in your chain. Some prefer to put it in the effects loop of their amp, if available.
  9. 9
    True Bypass - True bypass feature allows you pass your guitar sound unaltered when the pedal is off. The is almost always an essential feature to have
  10. 10
    Other considerations - Your budget and price of the pedal will always be an overriding consideration while deciding on the pedal to buy. In addition appearance, build, enclosure material, quality of components used, additional features like tap tempo, durability and the warranty offered by the manufacturer may play a role in your final decision.

Flangers

You are familiar with time effects such as delay and reverb. Delay effects become much more interesting when the delay time is allowed to change. Here we enter into the realms of delay modulation. 

The effect derives its name from the early methods used to create it. Same music recording was played on two reel to reel tapes simultaneously. The output from the two tape playing heads was mixed into a third recorder. Finger was put into the flange, spinning the reel on one machine and withdrawn, time and again, creating a varying time delay with the other machine. This resulted in a spacey, swooshing or jet plane sweeping sound as the harmonics add or cancel each other. 

Compact flanger pedals were marketed in the late 70’s with the intention to emulate complex studio effects. Some of the popular flange pedals include - Donner Jet Convolution, TC Electronic Vortex, EHX Stereo Electric Mistress and BOSS BF-3. 

Phaser Vs Flanger

Some players consider and call flangers as the big brother of phasers. It has a similar sweep and motion to it’s sound, albeit with more frequency altering modulation effects within that motion. While they can sound similar, confusing many, there is a big difference in the way they are created. Let us understand some critical differences between the two

  1. 1
    Both are modulation effects, but phasing works on varying phase delay making it frequency based effect, while flanging works on varying time delay and is solely a time based effect.
  2. 2
    In phasers, different frequencies are phase shifted by all pass filters by different amounts creating a notch filter. The peaks and troughs in the output are not harmonically related. In flanging the delay is applied equally to the entire signal and is uniform throughout. This creates a movable comb filter having peaks and troughs in linear harmonic series. Phasers have N/2 notches while flangers have many uniformly spaced teeth. For more notches in phasers you require more stages of filters.
  3. 3
    Flangers have more control on the inverse points of the out of phase relationship, thereby resulting in a more oppressive effect than phaser.
  4. 4
    Flanger modulation pedals require special Integrated Circuits (IC’s) to create enough delay for a true flanging effect. This may be beyond the ability of basic discrete analog components. Phase effect can be created by purely analog circuits.
  5. 5
    Flanging requires much more complex devices and involved circuitry. Hence, even basic flangers invariably have more controls. Whereas, some of the basic 4 stage phasers may have only speed control on them.
  6. 6
    Phase modulation effects are commonly used to enhance the texture of the sound. Hence it may be used for the entire length of your music. Flanger modulator pedal on the other hand creates a dramatic sound effect and may be used only on a specific portion of your guitar playing.

What Is A Modulated Delay?

If we subject a piece of music to a fixed delay of 50 ms, we get an effect known as a slap echo.The delay unit will delay the entire piece by this set delay time. This is known as delay without modulation. Some beautiful, powerful and very interesting effects can be created by changing the delay times using modulation effects on it. Delay subjected to modulation controls like rate, depth and shape with continuously changing delay times is known as a modulated delay.

How A Flanger Pedal Works

In flangers also, like phasers, the guitar input is split and each part follows a different propagation path. The dry or unaltered part goes straight to the output, while the second part passes through a delay line, where it gets subjected to delay modulation effect before mixing with the original signal to create the effect. All modulation effects require a simple but effective array of controls. Let us look at the set of control parameters for flangers.

Flanger_Block_Diagram

Controls On A Flanger

Similar to the phasers, low frequency oscillator waveform parameters like amplitude, frequency and shape govern the modulation process. The difference lies in the fact that a fixed delay gets modulated in flanging instead of the phase. The main controls are:

  1. 1
    Rate Control: As pointed out earlier, flanger effect has its origins in modulation of delay. Rate is the speed at which this delay time is changed. This change is within the boundaries set by another control “Depth”, discussed next. The rate control essentially varies the frequency of the LFO waveform.
  2. 2
    Depth or Range Control: Range Control defines the extremes of the delay, i.e, the shortest and longest delay times allowed, as a result of modulation. It varies the amplitude of the LFO waveform. Constructive and destructive interference associated with the short delays (< 20ms) results in a comb filter effect that further leads to the flanging effect. A short delay time of 5 to 15 ms is must for the flanger to give expected results. 
  3. 3
    Shape Control: It is the path taken by the device in changing the delay time. The path can follow a perfect sinusoid, a triangular, a square waveform or anything in between. Some delay units allow you to choose a combination of these. This control changes the shape of the LFO waveform. In extreme scenarios, the delay may have a random setting instead of traversing an orderly path between the extremes. 
  4. 4
    Regen or Feedback: This controls exactly what proportion of the delay unit output gets fed back to its input. This fed back portion of the signal gets delayed further on passing the delay unit again and creates an echo effect. Increasing the feedback will increase the resonance. Feedback can be in phase or out of phase and is called as positive or negative feedback accordingly. 

How Do You Use The Flanger Effect?

As discussed earlier, the metallic, jet engine like whooshing sound, sets a flanger apart from the phaser. Though it is possible to carry out flanging on a clean tone, most music players prefer it on a driven tone. The flanging effect is very subtle and sounds natural, when you try it on a clean tone, but clearly stands out on a distorted tone. In fact, you can try the flanging effect on a white noise, where it is glaringly obvious.

You will find that at slow speeds, the effect does not go over the top. Crank up the depth and the speed, it starts to create interesting warbling sounds, where the pitch goes up and down emulating a plane flying past you.This distinct rise and fall sound is the main characteristic of flanging. Flanging may thicken or provide more stereo width to the sound. 

Some popular songs With flanging:

  1. 1
    Are you Gonna Go My Way - Lenny Kravitz
  2. 2
    Barracuda - Heart
  3. 3
    Life In The Fast Lane - Eagle
  4. 4
    Bold As Love - Jimi Hendrix
  5. 5
    Cherub Rock - Smashing Pumpkins
  6. 6
    Run Like Hell - Pink Floyd
  7. 7
    Keep Yourself Alive - Queen
  8. 8
    Cowboys from Hell - Pantera
  9. 9
    Unchained - Van Halen
  10. 10
    Stockholm Syndrome - Muse.
  11. 11
    The Spirit of Radio - Rush
  12. 12
    Itchycoo Park - Small Faces

Listen to the iconic flanging tone having shimmering oscillations of the galloping guitar riff in the track Barracuda by Heart below

Things To Consider Before Buying Flangers

Many of the aspects like size, Digital or analog, adjustability & ease of use, inputs & Outputs, true bypass and other considerations are similar to those discussed for phaser pedals with very minor variations. Hence we will discuss aspects that are specific to flanger modulation effects.

  1. 1
    Subtle Vs Drastic Change: Flanger pedal is not for players looking for subtle effects.If you have the desire to experiment with big and drastic changes to create some fun sounds, go for it.
  2. 2
    Where to use the Flanging effect - It is commonly used in the following scenarios
  • In small portions of the song at the chosen moments, to recapture the interest of the audience.
  • While it is possible to use the flanger throughout the entire mix, it is done only on a limited number of bars to reinforce the dramatic aspect of the break.
  • To create a sense of movement.
  • It works well with modern metal, grunge and funk
  1. 3
    Pedalboard placement: The purists will advise you to put the modulation effects towards the end of the signal chain, but before the delay and reverb effects. However,  you can always be adventurous and try other placements. You may be able to extract more abstract sounds from your flanger.
  2. 4
    Voicing: This relates to the flavor of overall sound you want from your flanger. You can choose between the vintage flanging sound or the modern one.
  3. 5
    Tap Tempo: If you are an intermediate or advanced player, you may prefer the ability to tap in the tempo of the music you are playing. The effect then aligns itself to work in line with that tempo.

Read Our Reviews of Flanger Effect Pedals

Chorus

Best way to visualise the phenomenon of chorus is by imagining multiple guitarists playing the same part of the music together. In Spite of their best efforts, the players can never be in perfect sync with each other and will be out of time, ever so slightly. Even when playing the same note, the force applied on string by each of them will vary, inducing miniscule differences in the pitch.

This produces the Chorus effect, where different sounds played at almost the same time and very similar pitches appear to converge and perceived as one by the listener. This ensemble effect of many guitar players playing together is what a chorus modulation effect pedal tries to mimic. The successful implementation of chorus effects should ensure that none of the constituent sounds appear to be out of tone.

Some of the popular chorus effects pedals include TC Electronic Corona Chorus, EHX Small Clone, Boss CE-5 Chorus and MXR Analog Chorus. 

Is Chorus A Modulation Effect?

Delays are classified as long (more than 50 ms), medium (20 ms to 50 ms) or short (less than 20 ms). With short delays we get the radical comb filter effects, that on modulation gives rise to flanging. Longer delays result in a broad range of echo based effects. Medium delays are too fast for echo based effects and too slow for flanging effects and sounds like two players playing the same track. 

Chorus effect also uses the common multitrack technique of signal splitting into two copies like other modulation effects discussed so far. By adding a signal delayed by 30ms to the original signal, the chorus pedal creates a slightly asynchronous sound of two instruments playing simultaneously. 

When the delay times are modulated continuously, it’s length changes with pitch shifting as a side effect of the process. Constant increase in time delay results in downward shift of the pitch and vice versa. 

Chorus pedal varies the delay using a LFO. The back and forth variation of delay gives rise to the shimmering effect. At the same time, the consequential pitch shifting is equivalent to a small vibrato effect on the signal.

Chorus Pedal Controls

The main controls on the chorus pedal are:

  1. 1
    Rate or Speed: This control is similar to the one on flanger and controls the speed or the frequency of the LFO waveform. 
  2. 2
    Depth: This setting controls the amplitude of the LFO and consequently the intensity of the chorus effect. This defines how extreme the chorus warble is. It may also be called as the subtlety control on the pedal.
  3. 3
    Level: Most modern chorus pedals allow you to choose the proportion of wet signal in relation to the unaffected sound. This setting allows you to avoid that 1980’s over the top feel in the chorus effects.
  4. 4
    Equalization: Some of the pedals allows you to add brightness to your tone through the EQ control Knob. 

What Does a Chorus Effect Sound Like

Chorus enhances the clean tones to add texture and movement to your guitar audio. It also helps to bulk up the overdriven tones. You can add a little bit of the chorus effect to the lead tone to add color and thicken it up. 

Chorus pedals were very popular in the 1980's for rock as well as heavier genres. Metallica used them exclusively on the clean tone to contrast it against their high gain sounds. Steve Vai and Joe Satriani often used chorus on the overdriven portions of their tones to add some character to it. 

The level setting gives you an option to choose a more subtle and transparent effect in the low settings, while attaining a really thick sound in the higher ones.

Midway setting on the rate and depth controls will usually provide the characteristic chorus sound that gives your chords and tones a dream quality. Increasing the depth setting to ¾ position will give a semi effective Leslie rotating speaker effect.

Increase in the speed setting will result in faster shimmer or wobble of the effect. Very high setting will make the chorus pedal sound like a vibrato giving a very supernatural and haunting feel. “Black Hole Sun” number from Soundgarden with a very fast rate on its chorus effects gives a very unsettling and creepy feeling.

Chorus effect gets enhanced in a stereo rig, making the tone sound much fuller. Chorus has been one of  very widely and heavily used modulation effects, to the extent of being overused.

Some Popular Songs With Chorus Effects

  1. 1
    Welcome Home (Sanitarium) - Metallica
  2. 2
    Spirit of Radio - Rush
  3. 3
    Come As You Are - Nirvana
  4. 4
    Get Lucky - Daft Punk
  5. 5
    Walking on The Moon - The Police
  6. 6
    Don't Dream It's Over - Crowded House
  7. 7
    Master of Puppets - Metallica
  8. 8
    Purple Rain - Prince
  9. 9
    Paradise City - Guns 'n' Roses

Things to Consider Before Buying A Chorus Pedal

Many of the points to consider are the same as in the case of flanger or phaser. We will discuss the aspects that are different from the other two

  1. 1
    Use of Chorus Pedals: Some of the ways, you may make good use of the chorus effect in your music are:
  • It can be used to add subtlety, color, saturation or atmosphere to your clean tone, without being too overpowering
  • It can also provide some sustain and feedback to your soft guitar riffs.
  • As already pointed out in the Chorus sound section above, it can help you to get your lead stand out over the rhythm by thickening your tone and adding color to it.
  • It works really well with arpeggios by adding character to each note.
  • It is one effect that sounds really good with many acoustic-electric guitars.
  • They are considered to be ideally suited to pair with reverb and delay effects and usually works well with overdrives, phasers, flangers, and tremolos
  1. 2
    Analog Vs Digital: Analog chorus effects impact the full frequency band of your guitar signal resulting in a deeper sound. Digital pedals on the other hand are more versatile and can be tweaked to provide a greater range of sounds. Some players however consider their sound to be more synthetic. It is a matter of personal preference. 
  2. 3
    Position in the signal chain: General rule followed by most guitar players is to place modulation effects after the gain pedals, as stated in our discussion on flanger and phasers above, but before time based effects. This is due to the reason that modulation effects tend to smoothen the distorted signals and are more pronounced in this configuration. If you mostly play clean tones, you have the flexibility to place them before the gain pedal. However, traditionally chorus pedals have been placed in the effects loop of the amplifier, if it has one. This provides transparent sound retaining part of the unprocessed tone.

Read Our Reviews of Chorus Effect Pedals

Tremolo

Tremolo is a type of modulation effect in which the volume level of the sound is rapidly turned on and off at a particular speed and intensity. This gives rise to a pulsing effect that creates a sensation of oscillating volume control. To use purely technical terms, it means the amplitude modulation of the input guitar signal.    

Before we proceed further, let us first clarify two common confusions in the mind of beginners related to the Tremolo effect.

  1. 1
    The Tremolo effects unit has no relation with the Tremolo bar, found on many of the electric guitars like the Stratocaster. As a matter of fact, what the Tremolo bars on these guitars does is to create a Vibrato effect.
  2. 2
    The Tremolo effect does not raise or lower the pitch of the sound as the Tremolo bar does, which is actually a frequency based effect. It has nothing to do with amplitude modulation. The confusion exists in the industry as a result of mixing of the terms by Leo Fender who named the Vibrato effect creating bar on his guitars as the Tremolo bar and the Tremolo effect on his amps as the Vibrato effect.

These two effects were built into the tube amps much before their standalone effects versions. Tremolo has made a major comeback in recent years and is used in many numbers these days. Some of the very popular Tremolo pedals are Boss TR-2 Tremolo, EHX Super Pulsar and Wampler Latitude.

How Does A Tremolo Work

To conceptualize the working of a Tremolo, consider that your guitar signal is connected to an amp directly. If you turn the volume knob on the amp from OFF to ON position and back to OFF continuously, while somebody else is playing the guitar, you will get a fading in and out type of pulsing guitar sound. The speed of knob turning will govern whether the effect is smooth or an abrupt one.

Like in other modulation effects, the properties of the LFO waveform govern how the effect impacts your music. In this pedal, you will have at least the rate or speed knob and depth or the intensity knob. Many pedals in the market have additional controls than these basic controls like wave shape control knob, tap tempo etc to manage the finer details.

Tremolo Controls

  1. 1
    Rate or Speed Control: It changes the frequency of the LFO to vary the speed at which the volume will rise and fall. You can adjust the setting to match the speed with the tempo of your song.
  2. 2
    Depth or Intensity: This knob alters the amplitude of the LFO waveform and helps you fix the lowest volume or the limit of volume loss in your effect. You can go for a subtle variation or completely cut off the volume.
  3. 3
    Waveform Control: Waveform shape can play a massive role in how the sound from this effect finally turns out to be. The common choices in most stompboxes are Sine, Triangle or Square wave or any combination of these by blending. The impact of the common shapes of the waveform on the sounds produced by the effect is detailed below:
  • Sine wave: The rise and fall is faster compared to the triangular waveform but the volume stays near the maximum and minimum values for more time.
  • Triangular Waveform: The volume increases and decreases at a steady rate. Rise is immediately followed by the fall and vice versa, with no gap in between.
  • Square Waveform:  Use of square waveform makes the volume transition instantaneously from MAX to MIN value based on depth settings. It stays there for the half time period of the waveform and then goes back instantaneously to the MAX position. If the depth is set to maximum, the effect will make the volume alternate between ON and OFF, making for a very dramatic effect. This is akin to using a kill switch on your guitar that cuts the original signal from the guitar completely on activation. Only difference in this case is that you have to switch ON manually by releasing the kill switch.

Sound of a Tremolo

Tremolo creates a rhythmic effect that can work equally well on a clean tone, driven tone or in conjunction with other guitar effects. It works better with the longer chords and may not appear ideally suited for strumming, as the rhythm may not synchronize with tremolo speed. Though tap tempo is provided in many of the Tremolo pedals, it is difficult to use with strumming, particularly if you are a relatively inexperienced player and best left to experts.

It can provide dramatic effects using squarer waveforms for shorter durations. Triangular waveforms at low intensity settings can provide a subtle effect, more so at higher speeds. Tremolo’s have been used for full songs, but in fewer cases. Songs that highlight excellent use of Tremolo Effect are
  1. 1
    “Crimson and Clover” — Tommy James and the Shondells (1968)
  2. 2
    “Crush with Eyeliner” – R.E.M. (1995)
  3. 3
    “Born on the Bayou” – Creedence Clearwater Revival (1969)
  4. 4
    “Gimme Shelter” – The Rolling Stones (1969)
  5. 5
    “Rebel Rouser” – Duane Eddy (1958)
  6. 6
    “Howlin’ for You” – The Black Keys (2011)
  7. 7
    “How Soon is Now” – The Smiths (1984)
  8. 8
    “Between the Eyes” – Love Battery (1992)
  9. 9
    “Baby, Scratch My Back” – Slim Harpo (1966)
  10. 10
    “Bones” – Radiohead (1995)

Read Our Reviews of Tremolo Effect Pedals

Vibrato

Vibrato Effects are rhythmic modulation effects like Tremolo in which the pitch is slightly increased above or decreased below the original pitch. This change is at a particular speed or intensity to give rise to a warbling, underwater type of sound. It is like an oscillatory frequency control. 

Vibrato effects are readily available today in the following forms:

  1. 1
    In the standard stompbox style
  2. 2
    In the form of an expression pedal that allows you to control the intensity of the effect, much in the same way as you will do in a Wah pedal.
  3. 3
    Built into a multi-effects unit.

Vibrato effect is more aggressive sounding in comparison to Tremolo. It is best to use the Vibrato effect in a subtle fashion as an extreme vibrato effect starts to give a sickening feeling after you hear it a few times. The effect is characterized by the amount of pitch variation called the “extent of the vibrato” and the speed at which the variation in pitch is done, known as “rate of the vibrato”. 

The terms used to describe a subtle Vibrato effect are shimmer, swell, chorusey, or wash, while in more aggressive settings, it is known as warped or seasick. 

It is very essential to fully understand how much effect is necessary to complement the song and is not too less or too more. It is best used in moderation with very subtle applications. 

Some of the very popular Vibrato pedals are TC Electronic Shaker, Fulltone MDV3 Mini Deja Vibe 3 V2 and Boss VB-2W.

Chorus Effect Vs Vibrato

In Chorus effects also, modulation of medium delay results in pitch shifting like vibrato. The difference lies in the fact that in chorus pedals, the modulated signal is mixed with the original signal to get a blend of the two signals, while in vibrato, we only have the modulated or wet signal without any blending. 

If you set up the pedal correctly, you get much more natural sound in comparison to a Chorus pedal. However, due to inherent similarity between the two, many manufacturers produce combo pedals in which they offer both these audio effects.

Why do we use Vibrato Effect

The modulation creates a sense of movement and rhythm due to oscillatory variation in the pitch. Also, with the change in pitch, the notes may appear richer and stronger, adding expression, depth, ambience and color to the music. 

The basic controls on any vibrato unit are the same as those on a tremolo pedal - Level, Rate and intensity with the same functions. Low intensity settings will provide a more subtle effect, while higher settings deliver a warped sound.

As already noted above, the effect is best used subtly and occasionally and should not be overused or kept on all the time. Analog vibrato pedals are usually more expensive than the digital ones.

Some Popular Songs Featuring Vibrato Effect

  1. 1
    Knights of Cydonia - Muse
  2. 2
    Grown Up Wrong - The Rolling Stones
  3. 3
    Born on the Bayou - Creedence

Read Our Reviews of Vibrato Effect Pedals

Uni-vibe

Univibe has been a very popular effect that has created many iconic tones in the hands of players like Jimi Hendrix, Robin Trower and David Gilmour. 

In the 1960’s, many guitarists started going for large Leslie cabinets.These cabinets contained a rotating drum and a speaker that created a big swirling sound for compact Electronic Organs like Hammond organ. Many effect designers of the time tried to emulate the effect of the Leslie speakers in a compact pedal. As a result, Uni-vibe was created in 1968 by Japanese company Shin-ei.

These effects did a poor job of what they had originally set out to do, i.e. emulating rotary speakers, but what came out was so inspiring and special, that it continues to fascinate the new generations of players with its hypnotic tones till today. On the negative side, the original uni-vibe lacked the true bypass switching and produced a lot of noise.

Uni-vibe pedal gained tremendous popularity, with its use by Jimi Hendrix on songs “Voodoo Chile” and “The Star Spangled Banner” in his Woodstock performance. 

What is a Uni-vibe?

Uni-vibe is a phase based modulation effect similar to other modulation effects discussed above, in the sense that it also splits the original into two signals. Second part is phase shifted similar to a phaser and combined with the original part in the end. 

It is basically a four stage analog phaser but sounds different from most phasers. It makes use of an LFO to produce a sweeping effect and a pulsating light bulb with four photocells to control the speed of sweeping. The speed of pulsing of the bulb is controlled by the rate knob and brightness by the depth. Brighter the pulse of the bulb, more dramatic is the effect. Speed of the effect could also be controlled by an external expression pedal. 

The earliest implementation of the pedal used discrete transistors as against the op amps that most phasers use. Uni-vibe’s unique sound is often attributed to imperfections of the discrete transistors and residual distortion of the transistor stages.  

Some of the popular Uni-vibe pedals include - TC Electronics Viscous Vibe, MXR M68 Uni-vibe, Moen Shaky Jimi Vibe, EHX Good Vibes and Fulltone Custom Shop MDV - 3.

Sound of a Uni-Vibe

It is very common for people to mistake a Uni-vibe with chorus or phaser effect, as all of them are modulation effects that have some level of similarity in their operation.

Most of the earlier Uni-vibes had a toggle switch to choose between chorus & vibrato. However, modern Uni-vibes usually replicate only the chorus mode.

Uni-vibe produces a characteristic throbbing sound when set at sufficient volume. This  swirling and throbbing sound is the give away to identify Uni-vibes from these other effects. Chorus and phasers sound a lot more subtle and while they can get close at some settings, they can almost always never match the Uni-vibe.

  1. 1
    At a chorus setting with low speed, level and intensity, Uni-vibe may sound like a phaser.
  2. 2
    In vibrato mode with low speed, level and intensity,, the effect is barely noticeable. 
  3. 3
    With medium speed and intensity in chorus mode, throbbing sound, begins to appear.
  4. 4
    In the same settings in vibrato mode, the effect, though noticeable, is still very subtle in comparison to the chorus mode.
  5. 5
    Towards, the higher speed and intensity settings, the effect really starts overwhelming the original tone. In earlier times, players used an expression pedal to increase and decrease the speed. Most modern Uni-vibes don't offer expression pedals any more. 
  6. 6
    You will get full vibrato effect at these higher speed and intensities

Placement of Uni-vibe in the signal Chain

When it comes to the placement of modulation effects on the pedalboard in general, you will find varying opinions and Uni-vibe is no exception. Many players feel that Uni-vibe performs best before the gain effects as it makes them sound harsh and thin, particularly the heavy overdriven tones or fuzz sounds. You get warmer and natural sounding tones by using it before the gain pedals. 

Gilmour used Uni-vibes with mild overdrive on a clean sounding amp. Jimi Hendrix on the other end of the spectrum, used a Fuzz pedal before the Uni-vibe and fed them to a cranked up Marshall, generating dark overdrive tones.  

This effect works best with a fair bit of volume.Throttle the volume and you get muffled, thin and even flat tones out of your Uni-vibe. Higher volumes on your amp and adding a clean booster gives you a more dynamic sound with a lot of bite.

Popular Songs Featuring use of Uni-Vibe

  1. 1
    Machine Gun - Jimi Hendrix
  2. 2
    Bridge of Sighs - Robin Trower
  3. 3
    Breathe - Pink Floyd.
  4. 4
    Woodstock Performance - Jimi Hendrix.

Conclusion

I hope that the above article on the modulation effects has provided you with all the information that you were looking for. I had tried to present all the essential and relevant information about these effects at one place. If you would like to know further or have any doubts about them, please put your comments below and I would be happy to answer in a reasonable time frame.

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