Modulation Effects

• DAW


  Digital Audio Workstation
• Modulation sources


  • Low frequency oscillator (LFO)
  • Input signal amplitude
  • ADSR style envelope generator
  • Expression pedal
  • MIDI data
  • CV signal
• It's sometimes possible to combine modulation sources for more complex control signals, or to modulate modulation sources
• You can use DAW automation to modulate almost any plug in parameter very precisely
• Tremolo


  Modulation of signal level
• Tremolo has been built into many guitar amps and pedals and produces a pleasing 'undulation' at low modulation depths, but a stronger pulsing or even a 'chopping' effect when the depth is greater
• Tempo sync'ing the modulation rate

  Makes it easy to use tremolo to reinforce or contribute to the rhythmic feel of the track
• Sine wave modulation


  Produces the familiar pulsing effect
• Square wave modulation


  Provides that more strongly defined chopping character
• Offsetting the modulation waveform in time (often by adjusting a 'phase' control) means you don't necessarily have to have the loudest sound sitting right on the beat
• Where a deep tremolo's LFO is configured in opposite polarity on the left and right channels of a dual mono signal it will create an auto pan effect
• Vibrato


  Modulation of pitch, not volume
• At the heart of the vibrato effect is a very short delay line, and modulation of the delay time creates the familiar effect
• Chorus


  Mixing the dry signal with a slightly delayed version of the pitch modulated signal to create the illusion of two or more instruments playing the same part at the same time
• Chorus was used extensively in the 1970s, through the '80s and into the early '90s in pop, new wave, shoe gazing and glam rock to grunge
• Ensemble effect


  Multiple subtle chorus effects running at the same time but at different modulation rates to disguise the cyclic nature of the more basic chorus
• Ensemble effects were based on the chorus/vibrato circuit found in the Roland JC-120 amp, the Roland SDD 320 Dimension D processor, and the Yamaha SPX90 processor's Symphonic patch
• Flanging


  Modulating the playback delay time for a duplicate of the source, creating a comb filter that moves up/down the spectrum as the delay changes, causing the familiar 'whoosh' sound
• Flanging can create a very psychedelic trippy sound on vocals but it can work its magic on anything that has a rich harmonic content such as distorted guitar or synth parts
• Genuine tape flanging can result in a 'delay' moving before the dry signal, which requires a delay in a plug-in or stompbox flanger to emulate the 'through zero' flanging effect
• Using a flanger to affect only a reverb or delay send, with the flanger before the reverb, can add a useful texture to the reverb without the flanger's sweeping sound being obvious
• Genuine tape flanging


  • Modulating the speed of two tape machines can result in a 'delay' moving before the dry signal
  • Requires a delay to emulate the 'through zero' flanging effect
• Overt flanging


  Used more sparingly or subtly in modern productions
• Using a flanger to affect a reverb or delay send


  1. Put the flanger before a reverb so the reverb will smear the effect

  2. Adds a useful texture to the reverb without the flanger's sweeping sound being obvious
• Switching off the flanger's internal LFO modulation and adjusting the delay time


  • Produces a static comb filtering effect
  • Metallic ringing tone, especially at higher feedback settings
  • Useful treatment for some rhythm parts, such as drum loop 'toppers'
  • Feature of the original EHX Electric Mistress Flanger
• Phasing


  • The phaser's wet signal passes through a number of phase shifting stages
  • Fewer peaks and troughs than in a flanger's comb filter
• Uni Vibe


  Smooth, watery sounding variation on the phaser effect
• Artists who used the Uni Vibe

  • Jimi Hendrix
  • David Gilmour
  • Robin Trower
  • Pearl Jam
  • Smashing Pumpkins
  • Queens Of The Stone Age
• 'Barber's pole' effect


  Impression of perpetual motion in one direction, with the filtering effect always moving up or always down in pitch
• Rotary speaker


  • Low frequencies directed by a rotating drum
  • High frequencies directed via a rotating horn
  • Drum and horn run at different speeds
  • Doppler shift, amplitude modulation and complex filtering
• Less complex rotary speaker designs

  • Vibratone
  • Gibson Maestro Rover RO 1
• Plug-ins can offer interesting variations on the rotary speaker effect
• Artists who used rotary speakers

  • George Harrison
  • Dave Gilmour
  • Alan Parsons (on Pink Floyd's Dark Side Of The Moon)
• Slow rotary speaker emulation


  Interesting alternative to a chorus or phaser effect, including to process a reverb or delay aux channel
• Fast rotary effect


  • Rapid trilling sound
  • Lends an organ-like quality to most keyboard sounds
• Modulated filters


  • Can be controlled by LFO or envelope
  • Wah wah pedal is a modulated band pass filter effect
  • Envelope filter of a synth works in a similar way
  • Dedicated pedals like the EHX Q Tron can control the filter from the input signal's envelope
• Uses of modulated filters

  • Funk rhythm guitar or bass parts
  • Soft attack effect on notes or chords (as used by Mike Oldfield)
  • Alternative to phasing or rotary speaker effects
• Ring modulator


  • Takes two inputs and outputs their sum and difference frequencies without the fundamentals
  • Can produce an alien, unmusical sound
• Vocoder


  • Imposes the spectrum of one input (the modulator) as a complex filter on the other (the carrier)
  • Produces the 'talking keyboard' sound
• Talkbox


  Instrument sound is routed through a tube into the performer's mouth, allowing the instrument to 'talk' by mouthing vowel shapes or words