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TZP - Through Zero Phasing?

Started by frequencycentral, July 31, 2010, 08:07:56 AM

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frequencycentral

July 31, 2010, 08:07:56 AM
So, if we take an 8 stage phaser and process the dry signal through 4 fixed allpass/phase-shift stages before mixing it with the wet signal?
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earthtonesaudio

#1
July 31, 2010, 09:01:24 AM
...This seems like something Moog would have done.  ...Which means it is probably a great idea.



Of course you could really turn the tables and send the "dry" signal through a short, fixed digital delay line.   :icon_mrgreen:

frequencycentral

#2
July 31, 2010, 09:11:11 AM
I'm guessing that delaying the dry through half the number of stages that the wet passes through would be most desirable, and also using the same capacitor values as are used it the wet stages. That way real time (dry) is delayed by half the time of the wet. So real time is always late, and the wet signal can be delayed into the past or prelayed into the future with respect to real time. Will I need a DeLorean do you think?
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nelson

#3
July 31, 2010, 09:16:16 AM
Quote from: frequencycentral on July 31, 2010, 09:11:11 AM
I'm guessing that delaying the dry through half the number of stages that the wet passes through would be most desirable, and also using the same capacitor values as are used it the wet stages. That way real time (dry) is delayed by half the time of the wet. So real time is always late, and the wet signal can be delayed into the past or prelayed into the future with respect to real time. Will I need a DeLorean do you think?

No, but the allpass stages in the regen path will need flux capacitors.
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Mark Hammer

#4
July 31, 2010, 09:23:52 AM
TZF works because ALL frequencies are delayed by the same amount of time.  In the case of phasing, the notches are produced because SOME of the frequencies are phase-delayed more than others.

In the case of flanging, the number of notches produced vary as a function of delay.  In the case of phasing, the number of audible notches may alter slightly, depending on where you are in the sweep, but the number of actual notches produced remains constant.  So, at the very top end of its sweep, a 12-stage phaser will produce 6 notches, but maybe only 3 or 4 of them will fall within the passband of the pedal, the frequency spectrum of the instrument itself, or the speakers.  (Of course if you set the sweep width suitably, it won't sweep high enough for those other notches to disappear.)  As it starts sweeping downward, you may begin to hear all 6 notches, but no matter how low it sweeps, 6 is all you're going to hear.

In the case of TZF the entire passband is delayed by the same amount.  If the delay is anything OTHER than zero, even at the highest point in the sweep (shortest possible delay) there will be notches/cancellations produced, but they will be so high up in the spectrum that you won't hear them.  Should the minimum delay become zero, however, there can be a point at which - if the modulated signal is opposite phase - the dry and wet cancel each other out completely.  The point where the modulation passes "through zero" introduces that confusing hey-where-did-it-go sensation.

There is, as I understand it, no equivalent in phasing, simply because the amount of delay is not identical across the entire passband.

I'm not saying it wouldn't produce something interesting, but it won't do what some here may be thinking.

StephenGiles

#5
July 31, 2010, 01:03:53 PM
Eventide did this with their Instant Phaser. The circuits are kicking around somewhere.
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