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How Guitar Pedals Work

Make It Weird: Modulation Pedals

Back in the 1940s, Don Leslie developed a speaker cabinet that split a signal between a 15-inch drum speaker and a high-end horn. The drum and horn rotated at different speeds in opposite directions, producing sounds which revved from slow to shimmering as the speakers rotated in and out of phase with each other. Attempts to reproduce these sounds resulted in the first modulation effects. Studio trickery, such as the kind of manual tape flanging the Beatles used on "Lucy In The Sky With Diamonds," also provided inspiration for future modulation pedals [source: Hunter].

Modulation effects work by disturbing a signal's pitch and/or frequency to create everything from spaceship sounds to classic vibrato. Popular types of modulation pedals include:

  • Phasers. A phaser pedal splits a signal and plays back the two paths at different wavelengths to produce a spacey sound, like the one on the drums in Tears For Fears "Head Over Heels." (Listen for the drum fill as the song heads into the bridge.)
  • Flange. Flange is a lot like phaser, but with more of a sweeping effect. Eddie Van Halen used flange so often that Dunlop eventually engineered a flange pedal, the MXR EVH-117, based on his guitar sound.
  • Vibrato and tremolo. Though they sound similar, vibrato and tremolo are two completely different effects. Tremolo is actually a dynamic effect, relying on variations in a note's volume to produce a shuddering sound. Vibrato is modulation's answer to tremolo; small, fast pitch changes result in a vibrating sound. Guitars with whammy bars enable players to produce vibrato manually.
  • Octave divider. Octave pedals output your signal in a higher or lower octave. Jack White uses a DigiTech Whammy octave pedal to make his guitar sound like a bass on the White Strips song "Seven Nation Army."
  • Ring modulator. Used by avant-garde musicians in the 1950s, ring modulator effects mix a source sound with sound from an internal oscillator to create signals that are mathematically related. Ring modulation results in a variety of noise ranging from dissonance and grinding to metallic or bell-like tones.

Modulation effects produce some of the most interesting and bizarre sounds available for guitar. However, if you think pitch and frequency effects are fun, time-based effects will really blow your mind. Do you hear an echo? Head over to the next page and find out.