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Every Multi-effects pedal comes with a bunch of different Phasers and Flangers. While I can hear the difference between them when comparing directly, I could never point out what it is that makes them different.

What is it that they do differently while processing the signal?

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3 Answers 3

up vote 8 down vote accepted

A flanger adds a delayed version of the input signal back into itself. This produces a theoretically infinite series of equally spaced notches in the spectrum of the output signal (the spacing is 1/delay-time). Often this is referred to as comb filtering since a graph of the spectrum looks like a comb with downward pointing teeth. Usually flangers vary the delay time periodically; this shifts and spreads the locations of the notches while keeping the feature that there are a whole bunch of them all across the audio spectrum.

A Phaser achieves a similar effect but uses specialized electronics (often all pass filters) to put a smaller number of notches at specifically placed locations in the spectrum; how many and where depends on the make/model of the phaser. As with the flanger, the circuitry often involves a modulator that continuously (e.g. sinusoidally) varies the locations of the notches by shifting and/or spreading them.

To me, the main difference is that a flanger always produces notches everywhere across the spectrum, while a phaser only produces a limited set of notches.

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Going by this explanation and the examples provided by Alexander's answer, I think I got the picture of the differences. The main thing that I noticed is how the phaser seems to "cut" the sound, while the flanger kinda goes on in the background. Thanks! –  Gabe Aug 15 '13 at 16:55
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Good approach on touching the physics of both effects. But you've missed an important point: in the delay-based flanger, the periodical variation causes a substantial Doppler shift, so the flanger will "smear out" the frequency spectrum in addition to notching it. This doesn't happen much at all with the phasers, and that's what I would call the main difference. In a chorus, which is basically a special type of flanger, the focus is almost exclusively on the smearing, while the notches are mostly unwanted byproduct. –  leftaroundabout Aug 20 '13 at 0:08

Both phasers and flangers are "synth" effects. The incoming signal is analyzed, and additional waveforms, based on the source, are combined with or substituted for the "clean" signal to produce the effect. This makes them distinct from "gain"-based effects that work primarily by altering the amplitude of various components of the original signal directly, such as overdrive/distortion, equalization, notching (wah-wahs) etc.

The difference is that a phaser works on a phase delay, while a flanger works on a time delay. Similar in theory, but one is frequency-based, the other is solely time-based.

A phaser takes in the signal and splits it into at least two paths. One path is left unaltered, to be recombined before exiting the effect circuit. The other is put through an "all-pass filter". Its basic idea is not dissimilar from the tone pot on passive instruments in that it uses a capacitor, except here, instead of using the reactance qualities of a capacitor to create a "high-pass" or "low-pass" tone-altering filter, another property is used; the fact that AC current passing through a capacitor is phase-shifted by 90 degrees. The sound output from the all-pass filter is roughly the same signal strength as the input, thanks to a negative-feedback op-amp that corrects for the frequency-dependent attentuation through the capacitor, but each frequency component of the waveform is delayed by a different amount of phase with the original signal (with the "corner" frequency, typically controlled by the ratio of the capacitor's rating and the setting of a potentiometer, being altered by 90*). When recombined, the various frequencies combine constructively and destructively. Phasers often also include a modulating feedback loop, which varies the inputs to the all-pass filter and thus changes the corner frequency of the phase shift over time, producing a cyclical sweeping effect.

Phasers are the extreme of "chorus"-type synth effects, which use a similar circuit design, but the amount of variation produced is smaller (but often deeper; the circuit is split and phase-shifted more) to sound more natural.

A flanger works similarly, but instead of an all-pass, phase-shifting circuit, the altered branch of the signal is fed into a delay circuit that feeds it back out, more or less unaltered, after a specified number of milliseconds, regardless of frequency. In this regard, it's identical to an ordinary delay or reverb pedal, which are also time-based synth effects, but the delays are short (closer to reverbs than full delay pedals) and like the phaser, flangers include a modulator which varies the timespan of the delay, and the rate of change of that delay, producing a sweeping cyclical effect to the sound.

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I've never learned the science, There's definately a sonic distinction, I found a few videos with the difference, where they've been used in songs.

the difference explained and a practical demonstration:

Whenever I think of a phaser sound I always lead back to Satch(lead guitar in this song)

As for a flanger, I turn to Dream Theater's Goodnight kiss

Hope that helps! (note: if there are too many videos here let me know and I'll cut it down some)

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