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Comb filtering?
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| Arudius |
I'm curious if anyone has any recommendations for good VST or AU plugins for comb filters?
I'm a Mac user, so head's up, hehe |
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| Derivative |
emmm. You dont need a VST to make a comb filter effect.
Just bounce a stereo sound. On either the left or right channel (doesnt matter which one really) add a short delay of a couple of milliseconds. Just dont add the same delay to both channels.
What this will do is put the delayed channel slightly out of phase with the other channel in the stereo pair. If its a dual mono sound source, both the left and right channels will be identical and you get a comb filtering effect.
Alternatively you can take one of the channels in the pair and tune it out by a few cents. You will get that classic phasing 'sweep' sound instead. Tuning it out more, makes the sweep faster and more pronounced. |
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| Arudius |
| Ah very cool...I am going to try this now. I am wondering though...because I want to have full control over the comb filtering, so I can slowly sweep down and maybe hold before sweeping back up, or anything else I might want to do...how do you manipulate it that way? Thanks a lot Deriv. |
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| Derivative |
Comb filtering is not something you really 'control' like a conventional filter. By its very definition it causes alternating destructive phasing and amplitude spikes where both sounds move in and out of anti phase, across the entire spectrum of the sound.
Just delaying an audio channel is how a 'stereo widener' works. In order to create flanging/phasing sweeps, this can be done with an LFO and a high pass filter. Usually, alot of phasers and flangers have an LFO built into them so its not so much of an issue. Chorus, flangers and phasers are all basically comb filters with a few extra bells and whistles on. The difference in their application is determined by the amount of delay on the channel. A flanger is a phaser with a longer delay. A chorus is a flanger with a longer delay. And a digital delay effect is a comb filter with a delay long enough that the difference is heard as two separate sounds. |
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| Arudius |
All this time I've been asking here how to do this and that, all these effects BT does...and a lot of it was basically comb filtering...and with these very detailed explanations, i've mimicked very closely in Logic what I was going for.
You really helped me out Deriv...thank you very very much.:) |
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| -mk- |
Ahm.. Thats not a comb filter :confused: hmm, or it is kindof but when you do it on left and right channels its just "delay on the other channel". And it sounds wacky when played in mono... and thats not good.
You can control comb filters in a normal manner... doing sweeps etc. If it is a comb filter effect, not just delay on the other channel. I have no idea what vst's have comb filters but i use them daily on my Waldorf microQ and Clavias Nord Modular G2. You can do some crazy effects with them. |
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| Mikk |
Well that's exactly what it is from a technical view :)
From Wikipedia:
"In signal processing, a comb filter adds a slightly delayed version of a signal to itself, causing phase cancellations."
If you do it on stereo sound, the comb filter effect will take place after the sound leaves your speakers. (Don't really know how that would sound on headphones..) Also it will produce some out of phase stereo effects. If you combine the delayed sound with the other into a mono sound, the effect will be on your audio data. But it's basically the same thing anyways.
If you have comb filter effect on a synthesizer or as an effect I suppose it may have some other adjustments so you can control the effect better. |
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| Derivative |
Comb filtering is the basis of alot of effects. As mentioned before, choruses, digital delays, phasers and flangers are all based on comb filtering.
Someone mentioned in another thread how BT gets these lush pluck sounds - hes basically adding a long reverb tail to the synth and gating the output so it colours the sound with the verb but cuts off the reverb tail which would otherwise muddy subsequent notes and cause all kinds of phasing problems to occur somewhere further down the line, in the mix.
Alot of these neat sounding tricks and effects all come back to the same principles. Phase modulating processors (based on comb filters), frequency attenuation (based on filters) and dynamics processors (compressors and gates).
You can add various other modules like these to the signal chain to create more complex effects.
A phaser for instance is typically a comb filter with a phase splitter to generate a +LFO and -LFO. Changing the Phase init changes at what point along the horizontal axis of the waveform, it starts its oscillation from. Then you can put a high pass filter in series after the +LFO to limit the destructive phasing to certain frequency ranges.
And yea, you can build a crude phaser just by generating a stereo sound, delaying one of the channels in the stereo pair by less than 1 millisecond to get a comb filter then sticking a phase splitter straight after it. If your synth building or coding is good you can even build a basic FIR filter (i.e. write the entire process on DSP) and stick it in series after the the +LFO or -LFO and you have a rudimentary phaser without using any plugins or buying any expensive stompboxes.
The biggest problem with VST effects and outboard, all in one processors is that people grow up making music on these things and they have no idea of the signal chain inside these things. I would say it can be damaging because you get alot of people that dont realise that all these complicated phaser plugins are simply comb filters, LFOs and FIRs. There is a tendancy to think of all these things as separate processors - a phase, a comb filter, a filter, an oscillator. But really you can boil everything down to modules which alter the 3 properties of sound - amplitude, frequency and phase.
The most basic of these modules is the gate, the filter and the comb filter, respectively.
Ever use a multimode filter before? IF you have, you will know that you can build pretty much any frequency/phase modulating effect on one. Wah Wah pedal effects, phaser effects, chorus effects, stereo delays, wobbling sounds etc etc.
The genius of it is that it is all incredibly simple when you work out how its done - like most of the great inventions when shown how they work - 'if only I had thought of doing it like that!'. The important thing that separates them from us is that they thought of doing it on initiative and we didnt.
I recommend reading as much as you can on the subject and peripheral subjects. Its a cliched expression but knowledge really is power. If you do the homework, you will find using all of those tools makes much more sense later on and you start to learn every tiny detail in the sound and what you are affecting by changing a variable.
I recommend reading this mini article on the subject of phasers:
http://www.harmony-central.com/Effe...Phase_Shifting/
| quote: | | Ahm.. Thats not a comb filter hmm, or it is kindof but when you do it on left and right channels its just "delay on the other channel". And it sounds wacky when played in mono... and thats not good. |
Yes, phase modulation to a greater or lesser extent destroys mono compatibility. But if you listen to alot of modern records there is alot of dynamic stereowidth and phase modulation going on. Theres a soundclip of the end of flaming june somewhere around here (very recent) and if you take a listen to that pretty much every sound (bar 1 or 2) in that clip is panned off centre. Quite a few of those sounds have phase modulation effects on them and even more of them are progressively widened in stereo. I think I can even hear some sounds getting wider and narrower in stereo too.
Its so difficult to create the illusion of 'real space' without working with stereo width and phase. you cant really do it with just amplitude and frequency alone. And whether you like BT or not, he is very good at making his records sound as if they are playing from a real live space. Sounds are swooping around all over the place and coming at you from all different directions. Thats part of the great art of mixing - having all of these instruments moving around each other and coming at you from all angles without sounding weird or causing so much destructive phasing you completely lose mono compatibility.
Nine Inch Nails did that alot with 'Broken' and it comes with a 'not mono compatible warning.' Sure enough, sum both channels for the song 'happiness in slavery' to mono and take a listen. Whole parts of the track disappear mid mix! Thats some serious destructive phasing. However in stereo it doesnt really sound weird and you dont really get that 'brains being sucked out of your ears' sensation when you listen to a record thats phasing all over the place. Thing is, theres never an instance in that tune where the destructive phasing is so complete you are left with a 'hole' in the centre channel. Its very well mixed and theres alot of dynamic elements moving around so you never get that brainsucking sensation for very long.
In the end, it still comes down to how you plan your mix and how you keep a balance of all the instruments from left to right and quiet to loud, front to back. |
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| -mk- |
| quote: | Originally posted by Derivative
Yes, phase modulation to a greater or lesser extent destroys mono compatibility. But if you listen to alot of modern records there is alot of dynamic stereowidth and phase modulation going on. Theres a soundclip of the end of flaming june somewhere around here (very recent) and if you take a listen to that pretty much every sound (bar 1 or 2) in that clip is panned off centre. Quite a few of those sounds have phase modulation effects on them and even more of them are progressively widened in stereo. I think I can even hear some sounds getting wider and narrower in stereo too.
Its so difficult to create the illusion of 'real space' without working with stereo width and phase. you cant really do it with just amplitude and frequency alone. |
There's other methods for stereo widening that dont affect the mono compatibility. Personally i think the very very very old trick to delay the other channel from a stereo pair is useless and a very bad mixing technique. It destroys the tracks mono-, radio- and club-compatibility. Not a nice equation.
I wouldn't even count that technique as a comb filtering... referring to the definition, you don't add the signal to itself. Not even if you think of the space around you as the place for mixing signals.. remember that stereo has two different signals(ok they could be the same too, but thats basicly mono then).
Better techniques:
1. Normal "Chorus" effects(like kjaerhus classic chorus vst, check it out, very good.. and free)
2. Different osc's of a synth sound play on left and right channel, or stereo unison etc.
3. Two comb filters, one on each channel of a stereo pair, filter intensities modulated with an lfo to opposite directions... |
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| Derivative |
| quote: | | you don't add the signal to itself. Not even if you think of the space around you as the place for mixing signals.. remember that stereo has two different signals(ok they could be the same too, but thats basicly mono then). |
Yes you do. Comb filtering is a result of phase shifting. For that you need 2 discrete waves.
Stereo and Dual Mono, You can use either and both will have different results in terms of what gets filtered but thats to be expected if the left and right channel isnt identical.
*All* stereo wideners are based on comb filters. Theres no getting around it. Widen any sound enough using any widening/comb filter plugin or the method I described above and you will get destructive phasing.
Also, you are vastly overstating the effect of stereo widening and phase modulation on mono sound sources and making them unplayable. Thats far from the truth. It does not make the tune unplayable in clubs. You can listen to suburban train in a club and most of the song has some element peaking in antiphase - its almost inevitable when you have enough instruments in the mix and you need to fit in under 0 dB.
The only time phase modulation becomes a problem is if it is applied to bass and only bass. Sub and bass is omnidirectional and widening it makes it sound strange. The only other time it becomes a nuesence is when you have have too much destructive phasing going on, such that when the track is summed to mono, certain parts of the sound disappear. This is as much down to poor mixing rather than anything else. Its common for dance tracks to have the kick drum and bass centred and all the other instruments panned and widened around them. |
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| -mk- |
| quote: | Originally posted by Derivative
Also, you are vastly overstating the effect of stereo widening and phase modulation on mono sound sources and making them unplayable. Thats far from the truth. It does not make the tune unplayable in clubs. You can listen to suburban train in a club and most of the song has some element peaking in antiphase - its almost inevitable when you have enough instruments in the mix and you need to fit in under 0 dB.
The only time phase modulation becomes a problem is if it is applied to bass and only bass. Sub and bass is omnidirectional and widening it makes it sound strange. |
Yeah maybe i am overstating the effect. Just don't use that delaying technique mentioned before on anything imortant in the mix, as it will not be heard in clubs, or mono-radio.
Btw. I widen my bass sounds.. |
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| Derivative |
Yea some artists do. I notice that Infected Mushroom started to do it on IM the Supervisor - check out Muse Breaks. I think it sounds odd though and listening to it on headphones is a very odd experience.
Cosma widens some of his basses in stereo too - like on Cusanem but again, Im not sure if I like the effect. Cant complain really, as I dont know what would happen if it was centred and whether it would cause other issues in the mix. I love the song either way so I'd say he got away with it.
Further proof that any rule can be broken if you know what you are doing and know what effect you want to go shoot for. |
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