comb filters, flangers, phasers? anyone else think the terminology sucks with "phase" fx

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Hi - trying to get my head around "phase" fx. ie flangers, comb filters, chorus and phasers.

Seems like the terminology is all over the place and makes it all unneccessarily confusing to understand. First thing I learned. "Comb filters" aren't filters. They're delays that create the effect of a comb on the frequency response. As far as I can tell a flanger is just a "comb filter" with an lfo attached to the delay period. A chorus is also the same, however unlike a flanger you usually see a longer delay time, and (often) a partial polarity flip in the delayed signal to create a stereo effect.

Phasers are in fact the least similiar effect in this category, because they use "all-pass filters" which are filters that don't actually filter frequency, but stretch the "phase" (have i got this right?). Otherwise however they again use the lfo to move the delay period.

There doesn't seem to be a lot of standardization in the terminology, and when stereo effects and (real) filters are introduced into the design then we get a lot of variation between the plugs.

Have I got this right? What do you guys think?

This thought chain started as I was messing around with Melda's Mcomb.

ps: One more thing - it seems like "comb filters" as they are popularly used in electronic music etc - usually means an effect with much slower delay time than chorus/flanger - down to 100ms or so where it becomes very audible as a repetition.

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First thing I learned. "Comb filters" aren't filters. They're delays that create the effect of a comb on the frequency response
All the digital filters include delays as their principle of operation. Also, what defines filter better than it's frequency response?
because they use "all-pass filters" which are filters that don't actually filter frequency, but stretch the "phase" (have i got this right?).
Well, yes. It would be more precise to think about how these effects are made (using filters) and not what they really are. No one cares what phaser does with phase, it's all about modulated frequency response.
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All the digital filters include delays as their principle of operation.
Maybe I need to investigate what digital filters really are. Where do the similarities lie between a delay and a filter? And what really does an all-pass filter do? I have some research to do it seems, but please feel free to help me if you're feeling generous with your time. :-)

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rosko12 wrote:
All the digital filters include delays as their principle of operation.
Maybe I need to investigate what digital filters really are. Where do the similarities lie between a delay and a filter? And what really does an all-pass filter do? I have some research to do it seems, but please feel free to help me if you're feeling generous with your time. :-)
All-pass filter is a filter that causes a phase-shift, but does not have effect on the amplitude response: it passes all frequencies through equally, just possibly delaying some frequencies more than others.

A pure delay is really just a special case of all-pass filter where the phase-shift is linear (all frequencies delayed by the same amount), though it's typical to use the term "all-pass" to refer to the case where the filters have actual non-linear phase-shift (instead of pure delay).

In the technical sense, a lot of other stuff (including most reverbs too) is a "filter" but people usually use that term in the narrow sense to refer to the traditional EQ-type filters (or sometimes even more narrowly to low-pass/high-pass etc types) and other types of filters (where the primary effect isn't just shaping the spectrum) are called something else.

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Actually the comb filter is pretty clear way to explain relation between delay and frequency response.

The more advanced approach, how the people actually do it, is digital signal processing (DSP). This involves complex maths and in general is difficult to explain or learn on your own. That's why software synths are so expensive ;)

There are also analog-modelled filters, but these involve purely mathematical description and have no simple interpretation that I know of, unlike digital filters.
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I understand that a comb filter fits the description for both a delay and a filter, but as far as the rest goes I'm quite lost.

Is it possible to describe a high-pass filter as a sort of delay?

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I think you're looking at it the wrong way round: delay is used to implement a number of perceptual effects. But for most of these effects, it's lots of little delays acting in concert. This SOS article may help explain why it works: http://www.soundonsound.com/sos/apr11/a ... eption.htm

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What always trips me up is phasing vs. flanging.

I've always called the (originally) tape based delay filtering effect heard in psychedelic music as phasing, as did everyone else I met at college in the late 90's, and to us, flanging was basically phasing with feedback (usually done digitally).

These days, since the term "flange" refers to the edge of the tape, which was pressed to cause the tape to lag, I think what we CALLED phasing was actually flanging, and phasing these days seems to refer to using allpass filters to create a delay in certain frequency bands but not others.

It's a bit like the term "wavetable" which always meant "scannable waveforms" until synth design became a more open process (thanks in part to places like KVR where developers and players can connect) - then we realised "wavetable" in that sense was a sort of marketing term, and technically a wavetable is any kind of table (memory) with a wave in it :hihi:

Gah, words!
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Sendy wrote:What always trips me up is phasing vs. flanging.

I've always called the (originally) tape based delay filtering effect heard in psychedelic music as phasing, as did everyone else I met at college in the late 90's, and to us, flanging was basically phasing with feedback (usually done digitally).

These days, since the term "flange" refers to the edge of the tape, which was pressed to cause the tape to lag, I think what we CALLED phasing was actually flanging, and phasing these days seems to refer to using allpass filters to create a delay in certain frequency bands but not others.

It's a bit like the term "wavetable" which always meant "scannable waveforms" until synth design became a more open process (thanks in part to places like KVR where developers and players can connect) - then we realised "wavetable" in that sense was a sort of marketing term, and technically a wavetable is any kind of table (memory) with a wave in it :hihi:

Gah, words!
I always thought that "flanging" is an analog technique used with tapes, and "phasing" is a pretty generic term for an effect - desired or not - which cancels out some frequencies. Which means that phasing even occurs if you don't use a "phaser"...

Anyway, I rarely use "flangers" because they make everything sound so glitchy... :(
Last edited by Tricky-Loops on Tue Apr 22, 2014 3:04 pm, edited 1 time in total.

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Sendy wrote:What always trips me up is phasing vs. flanging.

I've always called the (originally) tape based delay filtering effect heard in psychedelic music as phasing, as did everyone else I met at college in the late 90's, and to us, flanging was basically phasing with feedback (usually done digitally).

These days, since the term "flange" refers to the edge of the tape, which was pressed to cause the tape to lag, I think what we CALLED phasing was actually flanging, and phasing these days seems to refer to using allpass filters to create a delay in certain frequency bands but not others.
When Itchycoo Park was recorded, the terms flanging and phasing were pretty much interchangeable I believe. Where things separated (I think) was when Mutron etc wanted to stick the effect into a pedal. Doing it with a delay in analogue electronics was trickier and more expensive than using an allpass, which looks very much like a Sallen-Key circuit and needs only a few active and passive components. But it still sounded like phasing, which was what guitarists wanted. Flanging was still more evocative of the tape-based trick. Also, by adding more to the circuit, you can do complex allpass filters that give you more control over the phasing sound, so the effects diverged even further.

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I like to call the "out of phase" delay with no feedback phasing because... well... that's what it is - messing with phase. It's also connected to the Steve Reich type of phasing, just on a millisecond/timbre level as opposed to the phrase level, so it makes sense that they're both types of phasing.

I guess at the end of the day the effects are all so similar that their terminology is going to have a lot of overlap. I tend to try and adapt to whatever convention the plugin/studio/people around me are using.
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Last time I checked, flanger was modulated comb filter. But this is pretty same effect as mixing two tapes at varying speed.

Phaser, however, is made of a number of all-pass filters with modulated delay, resulting in swirling, chaotic notches. It is different in a sense it's supposed to be unpredictable, while flanger has well-defined bahavior.
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rosko12 wrote:Hi - trying to get my head around "phase" fx. ie flangers, comb filters, chorus and phasers.
Seems like the terminology is all over the place and makes it all unneccessarily confusing to understand. First thing I learned. "Comb filters" aren't filters. They're delays that create the effect of a comb on the frequency response. As far as I can tell a flanger is just a "comb filter" with an lfo attached to the delay period. A chorus is also the same, however unlike a flanger you usually see a longer delay time, and (often) a partial polarity flip in the delayed signal to create a stereo effect.
Phasers are in fact the least similiar effect in this category, because they use "all-pass filters" which are filters that don't actually filter frequency, but stretch the "phase" (have i got this right?). Otherwise however they again use the lfo to move the delay period.
There doesn't seem to be a lot of standardization in the terminology, and when stereo effects and (real) filters are introduced into the design then we get a lot of variation between the plugs.
Have I got this right? What do you guys think?
This thought chain started as I was messing around with Melda's Mcomb.
ps: One more thing - it seems like "comb filters" as they are popularly used in electronic music etc - usually means an effect with much slower delay time than chorus/flanger - down to 100ms or so where it becomes very audible as a repetition.
A comb filter is the result of mixing a time delayed copy of a signal with the original one.
So you are mostly right:
Flanger is the name of an effect based on a time modulated short delay (3ms), causing a one-comb filter effect in the mixed output.
Chorus is an effect based on a time modulated medium delay (20ms), causing a detuned signal doubling (no audible comb filter).
A phaser is working by delaying the signal for (frequency-depending) fractions of ms (phase shifting of the waveform) - this is done with modulated "all-pass-filters" (despite of the name they may do filter some frequencies), giving the effect of several comb filters when mixing with the original signal.
All these effects can be done with analog or digital technique. Only the first two can be done with two tape machines, as there is only one delayed signal.
A phaser could be done with several short delay lines, but in hardware it's cheaper to use filters. And because the filters "delay" (phase shifting) is frequency dependend, the effect is more interesting.
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Have I got this right? - a digital all-pass filter has a value in ms/hz like any other filter (?). Increasing this value affects how "stretched" the phase becomes in time (?). Do the higher frequencies "stretch" first, or is the relationship more complex than that?

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