Modulation Effects
Thu, 23 Feb 2012

Modulation boxes, old and new
WHEN ANTHONY JACKSON LAID down the bass line for the 1973 O’Jays hit “For the Love of Money,” he created one of the most iconic bass moments in recorded history. The song’s signature lick, played on a Fender Precision through a Maestro PS-1 Phase Shifter, still sounds way cool 38 years later, and it helped usher in an era of bass players using modulation-based effects.

Phasers, flangers, choruses, tremolo, and vibrato are all considered modulation- based effects. Producing phase, flange, and chorus effects—the big three for bassists— involves splitting the input signal and modulating part of it with a low-frequency oscillator (LFO). Although they can sometimes obscure note defi nition in the lower registers, these three effects sound best when applied to harmonics, chords, slap-and-pop, or pickstyle techniques. Let’s take a look at some of the most popular modulation effects for bass players and see if there’s a swooshing sound that’s right for you.

While the general public first got hip to the phaser when it debuted as a handheld personal security device on the ’60s show Star Trek, the music world had to wait until 1971, when Maestro introduced its PS-1 Phase Shifter pedal. Phasers split the incoming signal and run a portion of it through an all-pass filter that reproduces a full-range copy while changing the phase relationship of various frequencies to the original. When the two signals are mixed, the out-of-phase frequencies cancel each other out, resulting in troughs and peaks in the frequency spectrum that change over time, creating a characteristic swirling effect. One important spec you’ll see listed for phasers is the number of stages they have, which indicates how many allpass filters the unit employs. The more stages, the more complex the effect. The Maestro is a 6-stage unit, while the classic MXR Phase 90 is a 4-stage effect. (Compare that to the Moog Moogerfooger MF-103, which has a whopping 12 stages.)

The controls on phasers can range from the ultra-simple, solitary speed knob on the Phase 90 to the Moog, which has controls for LFO (amount, frequency range, and rate), as well as sweep, resonance, drive, output, and switching between 6- and 12-stage modes. Phasers affect the fullrange signal from your bass, and it’s not unusual for them to take some of your low end. One solution is to use it in a parallel effect loop, which will make sure you’ll always have an uneffected clean signal at the same time.


To the casual listener, flangers sound similar to phase-shifters, but there are significant differences in how each effect produces sound and reacts. Both phasers and flangers split the input signal, but fl angers add a delay (less than 20 milliseconds) to part of the signal and then assign an LFO to the delayed signal, which modulates it up and down.

Because of the delay, the peaks and troughs that occur follow the harmonic series—essentially, what you hear when you pluck the harmonics on one open string, in order: 12th fret, 7th fret, 5th fret, etc. The sweeps passing through the harmonic series give the flanger that “jet plane taking off” swoosh that every bass player needs once in a while. Flangers typically have controls for rate (the speed of the LFO sweep), depth (the distance or width of the sweep), delay time (the length of the delay between the dry and effected signal), mix (the blend between the wet and dry signals), and resonance, also known as feedback or regeneration, which controls the amount of wet signal that gets re-routed back through the effect.

The evolution of features can be seen in these modulation effects.
Some of the more popular flange pedals include the Boss BF-3, a stereo flange with separate inputs for guitar and bass; the reissue of the classic Ibanez FL9; the MXR 152 Micro Flanger, a basic, small footprint model; the Electro-Harmonix Electric Mistress, which has a “Filter Matrix” mode that disengages the automatic sweep; and the TC Electronic SCF Stereo Chorus Flange pedal, which can operate in chorus mode as well.

Like the phase shifter, the fl anger affects the full frequency range of the signal, so you may want to try it through a parallel effect loop to preserve your bottom.

Chorus pedals, a staple in many a bass player’s collection, are undoubtedly the most popular effects in the modulation category. Chorus and flange effects are similar in concept, but chorus uses longer delay times on the split signal to achieve a discernable pitch change. The result can evoke the sound of multiple voices singing in unison, hence the name. Chorus effects can simulate the sound of the famed Leslie rotary speaker, mate of the Hammond B3 organ, so bassists use chorus to capture the vibe of that legendary keyboard. The shimmering quality of chorus, which lends itself nicely to fretless bass tracks, is a mainstay texture for ballads, jazz-fusion, and ambient music. It brings depth and dimension to harmonics, and does a nice job of hiding suspect intonation.

Chorus and flange both share similar features— effect level, speed, and depth controls are standard—but many chorus pedals incorporate other features that add to the tone palette. The DigiTech XBC Bass Multi Chorus, for example, has a VOICE control that splits the input signal up to 16 times for a thick, lush, multiple-voice chorus effect. The EBS UniChorus has simple DEPTH and RATE controls, but it also includes a switch that puts the pedal into flange mode, as well as pitch modulation mode—which increases the initial delay time, resulting in a more dramatic chorus effect. The Tech 21 Boost Chorus Bass pedal adds a tone control to warm up the effect, a DETUNE knob that produces a chorus sound without modulation (when speed and depth controls are set to minimum levels), and a level control with a healthy gain boost.

Like phase and flange, chorus affects the full frequency spectrum, and it can sometimes compromise your low end. Due to its popularity with bass players, however, many manufacturers offer bass-specific units that employ a built-in crossover that sends the chorus effect only to the high frequencies, leaving the bottom unaffected. The Boss CEB-3, for example, has a low-filter knob that varies the crossover point, allowing you to tailor the effect better for different situations; MXR’s Analog Chorus, which has separate wet and dry outputs, adds shimmer while retaining the bottom.

Digital effects use digital signal processing (DSP) to recreate the various delayed voices, resulting in more accurate, cleaner reproduction, while analog effects are generally thought to sound warmer and more organic. Modulation effects are yet another battleground for the ageold “digital vs. analog” forum threads, but perhaps it’s just a question of when and where: In a high-volume rock situation, with multiple effects daisy-chained, you might find that the pristine clarity of digital helps the effect cut through, while analog warmth might help you tame a bright, active bass or match a passive bass on a mellow gig. Ultimately, it’s best to try several models and judge for yourself. If you use multiple effects, bring them with you when you test-drive modulation effects, and keep your ears open for that elusive effect—overhead jet or underwater gurgling, for example—that’ll give you a special thrill.

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