What's the technical difference between a Phaser and a Chorus? What are they actually doing?

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I'm almost embarrassed to ask this question. I've been producing music for half of my life. I consider myself a decent authority on the depths of signal processing and generation.

But one thing I've never really known, and have been too embarrassed to ever ask, is what is technically going on in a phaser or a chorus. The sonic effect of either is obvious - anyone who has worked with either for very long will be able to immediately identify it when heard (except for some particularly ambiguous cases). But as far as what's technically going on, I've never been able to comprehensively wrap my mind around it.

Most explanations leave quite a bit to be desired - A phase shifter duplicates a signal and "shifts the phase" of the wet signal - okay, what does that mean? How do you shift the phase of a waveform without effecting it otherwise? I know (or at least, think I know) what the phase (its dynamic ("Y axis") value) of a waveform is, so shifting it outside of a delay function doesn't make sense to me. Apparently an all-pass filter is used to achieve this task but what does it actually do?

Opposed to a chorus or phaser, a flanger seems straightforward by comparison. It's a feedback loop with a short delay and the length of the delay is modulated. But that's what most chorus explanations make it sound like and chorus definitely has more going on.

Meowingly,
Chase

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Choruses work by constantly shifting the pitch of the signal just a little bit. I think BBD based choruses do it by changing the sample rate with an LFO and digital choruses do it by modulating the point in memory that a delay line is reading from.

Phasers change the phase of the signal with an allpass - which sounds like it's just a delay line, but the key is that allpass filters don't have the same phase response for all frequencies, higher frequencies might end up delayed by a millisecond whereas bass frequencies will be completely unchanged.

The flanger difference is more to do with the amount of delay time - the delay time for choruses will be a couple of milliseconds at most whereas flangers will be like 20ms, and the rate of change of the delay line will be slower than choruses. I think if you could put the delay time on a flanger to like 50ms you'd perceive it as a short delay rather than a flanging.

Not an expert so I'm probably not very informative on some stuff here, but I think it's worth trying to recreate some of these effects in Puredata or MAX, I did that when I was learning Puredata and it's pretty eyeopening how simple to make these effects are

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AFAIK, technically, the basis of flangers and choruses are actually pretty similar; a chorus just has a longer delay, so its perceived as 'thickening' the signal whereas the shorter delay of a flanger causes notch filtering that's more intrusive into the timbre.

Phasers generally are similar in result (notch filtering) to Flangers, though the mechanics of it might be different. A reasonable distinction, from geofex.com:

http://www.geofex.com/article_folders/p ... phase.html
Phaser vs Flanger

Given that both these devices produce their tones by causing notches in the frequency response of the device and sweeping those notches up and down, which is best? And what else does something similar?

It turns out that anything that gives you a moveable notch will come off sounding like either a phaser or a flanger. There have been devices that used multiple voltage controlled notch filters of various technologies to simulate a phaser's notches. Everything that does notches works. Some of these are more elaborate than the phaser they emulate.

The real difference between a phaser and flanger is that a flanger always produces a large number of notches that are an even multiple of frequency apart. Even phasers with large numbers of stages (I've heard of 20 stage devices!) can't compete with the multiple notches that a flanger puts out. The spacing of the notches is also audible as a change in tone, and it takes some careful trimming to get phaser notches spaced the same regular spacing as a flanger.
edit : oops just realised manducator linked to the same article. neffermind.
my other modular synth is a bugbrand

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Good shit, everyone. I wasn't aware how allpasses affected phase like that. That clears up phasers completely for me.

It looks like chorus is the most complicated of the 3. I'm reading up on how old guitar pedals cleverly used delay-lines to fake a pseudo pitch-bend to create that detuned double of the input.

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whyterabbyt wrote:AFAIK, technically, the basis of flangers and choruses are actually pretty similar; a chorus just has a longer delay,
Correct and a flanger normally has an amount of feedback.

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The Chase wrote: It looks like chorus is the most complicated of the 3.
Au contraire I would say it's (in its most basic form) the simplest of the bunch.

After all it's just a delay which has its length modulated by an LFO.

Think of it this way:

you have (say) some melody played by guitar. Now you record the exact same melody again with the exact same guitar. As good as you may ever play, without being a robot there will constantly be some slight timing differences between the two tracks, which will make it sound fuller than the single track. This is what a chorus does. Orchestras work exactly that way - ten (eg) violins play all the exact same thing and of course they usually play extremely tight, yet it still sounds very rich (okay, of course they also have slight intonation variations in addition to the timing variations).
"Preamps have literally one job: when you turn up the gain, it gets louder." Jamcat, talking about presmp-emulation plugins.

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jens wrote:
The Chase wrote: It looks like chorus is the most complicated of the 3.
Au contraire I would say it's (in its most basic form) the simplest of the bunch.

After all it's just a delay which has its length modulated by an LFO.
That's a flanger, my man :) Find a delay that allows super short times and where you can modulate the delay time with an LFO, and you'll recreate a flanger exactly.

In the research I've done recently it really seems like chorus is a blanket-term for a variety of pseudo-doubling effects that appeared in the 70's and 80's. Some are similar to flangers with feedback loops, others have staged voices like phasers, some have filters to avoid the jet-passing-by artifact that flangers have, some are feedback loops with an inversion stage in the loop for an interesting cancellation effect that also avoids this artifact.

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The Chase wrote:That's a flanger, my man :) Find a delay that allows super short times and where you can modulate the delay time with an LFO, and you'll recreate a flanger exactly.
Yeah, I said they could be very similar earlier. cf Datorro 'Effect Design' Part 2, Zolzer 'DAFX', et al
my other modular synth is a bugbrand

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