Changes

''Modulation Effects'' cover a variety of effects that use a low-frequency oscillator (LFO) to alter the tone over time in a cyclic manner.

''Phasers'' use a (often variable) number of all-pass filters (called ''stages'') to reverse the phase of certain frequencies, combining this phase-altered signal with the original signal to create nulls throughout the frequency spectrum. An LFO modulates how the stages operate and at what frequencies the nulls occur, sweeping them back and forth. Phasers can also use feedback on the phase-altered line to alter the make the nulls wider and less sharp. Some additionally have a mix parameter to determine the proportion of the dry (unprocessed) signal vs. the phase-altered signal.

* MXR Phase 90

''Flangers'' provide a very similar sound to phasers, but use delay and comb filters to create the nulls. The signal is split into 2 lines, with one line being delayed by a variable amount. When the lines are recombined, some frequencies will be out-of-phase, creating nulls at regular intervals (a comb filter). The delay time is linked to an LFO that changes the amount of delay cyclicly, so that the nulls sweep back and forth along the frequency spectrum.

The most important thing to be aware of is the ''manual'' control - properly setting this parameter is crucial to getting the sound you want.

* Boss BF-2

* Boss BF-3

* Electro-Harmonix PolyChorus

''Chorus'' effects provide a very spacious, slightly out-of-tune sound. They operate in one of two ways (or both). One way operates exactly like a flanger; however, it uses longer delay times and no feedback. Sometimes this is taken a step further by using stereo output, with both signals being delayed at different rates, creating a very spacious sound. In the case of stereo, there is no need to mix the signals back together, which can create a more natural sound.

Some choruses may combine both techniques.

* Boss CE-1

* Boss CE-2

The ''tremelo'' effect alters volume via an LFO, causing the sound to shimmer in and out. Generally, the only controls on these effects relate to the LFO, altering its rate, depth, or waveform. The waveform generally ranges from a Triangle or Sine wave where the sound fades in and out, to a square wave that sounds like someone is toggling an on/off switch quickly alternating between silence and full volume.

''Auto-Wah'' is simply wah pedal circuitry attached to an LFO, generating a constant wah-wah sweep. It is used to get wah movement that is generally faster and more rhythmically consistent than you'd want to produce manually with a traditional wah pedal.