Electric Guitar Tone Series: Phaser Effects Pedals

Electric Guitar Tone Series: Phaser Effects Pedals 

Having covered the more common effects of distortion and delay, we will now venture into the more peculiar territory of modulation effects.  The most common modulation effects are phase shifting, flange and chorus, which each split the guitar signal into two paths, shift the waveform of one path and then re-combine it with the original signal to create some degree of phase interference.  Each of these effects does so in different ways.  Phase shifting, the effect we will cover first, does so by inverting the phase (the pattern of peaks and troughs in amplitude of the wave) of certain frequencies.

How Does A Phaser Work?

A phaser pedal begins by splitting the guitar signal in two.  The first portion of the signal is left unaffected and thus called the “dry signal.”  The second portion is run through an “all-pass filter” which inverts the phase of a certain frequency in the the signal.  When a phase is inverted, the peaks of the altered wave occur at the point in time the troughs of the original wave once did, and vice-versa.  When the phase shifted signal is re-combined with the original signal, it results in phase cancellation (elimination) of that frequency from the overall sound wave.  The ratio of wet to dry signal determines the amount of cancellation of the given frequency.  A 50:50 wet/dry ratio results in full cancellation of the wave, while any less results in only partial cancellation.

A phaser uses a Low Frequency Oscillator to sweep which frequency or frequencies are phase shifted up and down the spectrum at the speed of the player’s choosing.  This results in the “swirling” or “whooshing” sounds associated with the phaser.  Multiple filters can be applied to the wet signal resulting in  multiple waves being cancelled at the same time, thus creating a “comb filter.”

Popular Phasers

MXR Phase 90- This four-stage phaser is perhaps the most identifiable and common on the market and will be forever associated with Eddie Van Halen.  With a single knob for speed control, it is also the easiest to use and therefore a great choice for beginners. 

Electro-Harmonix Small Stone Phase Shifter- Another classic four-stage phaser that contains only a single rate knob like the Phase 90, the Small Stone adds a color switch which controls the width of the notch placed in the frequency spectrum and the amount of wet signal fed back into the all-pass filters.  It can be heard on the many of the recordings of Smashing Pumpkins.

MXR Phase 100- This cousin of the Phase 90 is a ten-stage phaser  which contains the same speed potentiometer, but includes another knob to control the depth of the notch and width of the sweep.  This model allows an excellent balance of customization and simplicity. 

Boss PH-3 Phase Shifter- A digital phaser, this pedal allows for a large amount of customization.  While featuring the standard rate control, the also carries controls to manually set the depth, feedback and number of stages in the phasing effect, as well as a tap tempo function.  These controls will be expanded on in the next section.

Common Phaser Controls

Speed/Rate- Controls the pace at which the LFO moves the through the spectrum.  A faster speed results in more frequent oscillation, creating a warbling sound similar to a Leslie Rotary Speaker.  A slower speed creates a steady whoosh up and down the signal.  This is the only control on the Classic MXR Phase 90.

Depth- Controls the depth of the phase cancellation effect by controlling the ratio of wet to dry signal.  An even mix of wet and dry signal will result in complete cancellation of a given frequency.  If the wet signal is less than the dry signal, the cancellation will not be complete and only partially cancel the selected frequencies.

Feedback- Controls the amount of wet signal fed back into the all-pass filters.  This creates a wider notch in the frequency spectrum, thus making the peaks sharper.  Feedback can lead to a very dramatic phasing effect.

Stage- Some phasers have the ability to control how many notches are placed in the frequency spectrum at a given time. One notch is placed in the frequency spectrum for every two filters. Since analog phasers require a new piece of hardware for each stage, they typically do not have more than ten.  A digital phaser, however, can have stages a higher number as each filter does not take up any physical real estate.

Common Phaser Settings

Since phasers settings are highly dependent on the specific model, I have chosen to use the sample settings for the MXR Phase 100 as I feel if offers the best compromise of utility and ease of use.  There is also a virtual model of the Phase 100 in the Amplitube app called the Phase 10, which allows me to model these settings for my students. 

Photo Source: Jimdunlop.com

Slow and Deep- With the notches set deep and sweeping across the entire frequency spectrum, it becomes very easy to detect the phase effect in the sound.  This setting works well to create swirling chord sounds.

Spinning Speaker- Using a wide sweep with more shallow cancellation and a quick oscillation provides an imitation of a classic Leslie Rotary Speaker.

Medium Subtle- The short, shallow sweep at a medium tempo adds a little flavor to the guitar tone.  This setting pairs well with a light to medium overdrive.

Signal Chain Placement

Since phasing is a modulation effect it is typically placed after any gain-based effects such as overdrive, but before any ambient effects such as delay.  By placing the pedal after gain-based effects, the phase effect is applied to the added harmonics created by any distortion of the signal.  Therefore, when using amplifier distortion, phase can be run out of the effects loop on the amplifier.

Phasing is very versatile effect which has been used in many styles including country, rock, metal, funk, and pop.  It can be used equally well to layer rhythm parts or thicken solos.  When using a phaser, take the time to learn the capabilities and controls of your particular model as each will have a unique sonic responses.  Likewise, take care to balance anyother modulation effects with the rest of your signal chain, as they can easily become overwhelming or conflicting if not integrated to the appropriate degree.

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