Multi-voice vibrato

[Steben]

Two BBDs running anti-phase makes a *wonderful* Leslie-like sound, BTW, running at a slightly higher rate than Dim C Mode 4 at a lower mod index.

Ok, definitely worth trying then. But is it a way to get jet-flanging? Or is it better to use a set-delay BBD with a modulated delay so you raise the delay ratio. (like in MN3207 2.5msec to 50msec, but with a fixed one at 3msec for example and a modulated one at 3.5msec to 50msec, you would get real good flanging, no (resulting in 0.5msec to 47msec)?

[Mark Hammer]

One needs to distinguish a couple of things more clearly, here.

1) There is the total range of pitch deviation obtainable.  Let's say plus-minus two semi-tones as an example, for argument's sake.

2) There is the starting and end point of the deviated pitch, within the range possible; the deviation width/depth, if you will.

3) There is the synchrony of any deviated pitch.

4) There is the relative amplitude of any concurrently-derived pitch deviation.

If one had a multi-tapped BBD like an MN3011 or an MN3214 (where ARE those suckers?  Have any of you ever seen a real live one?), and the taps were employed/mixed-down in the absence of any dry signal, then modulation of the BBD would yield multiple pitch deviations, coming from each tap.  What I can't wrap my head around is whether what comes out of them is the same amount and range of pitch deviation, just sightly staggered in time according to tap, or whether what comes out of each tap is a different amount/range of pitch deviation, plus a time stagger.  In principle, if I whip a 256 stage BBD into the socket previously occupied by a 1024-stage BBD, the time-delay produced is divided by 4, and the amount of pitch deviation head is reduced by that proportion as well.  But that assumes that each device results in different amounts of real time modulation.  When a multi-tapped device enters the picture, things may or may not be different.  Like I say, I'm still trying to wrap my head around that.  Certainly, you can't modulate any of the taps by different degrees, the way you might be able to with separate BBDs.

Let's say, however, that the various taps produce different amounts of pitch deviation (longer taps producing greater pitch deviation), plus the time stagger introduced by the difference in tap points (stagger = #stages at tap point B minus #stages at tap point A times clock rate).  The pitch deviation you hear *most*, however, can still be altered, by adjusting the relative amplitude of each tap at the mixing stage.  Fade taps 4 through 6 to the background, and subtler pitch shift should dominate.  Reverse that mix, and more robust pitch shift should be heard.

In the case of allpass stages, though, there are simultaneous outputs available.  I realize that fixed delays can be introduced by complex allpass stages, but for all intents and purposes, the simultaneously available outputs of taps from an 8-stage phaser at stages 2, 4, 6, and 8 would be heard as simultaneous.  If these are all modulated by the same source, and by the same amount, my sense is that each tap would yield greater amounts of pitch deviation.  You could still mix them down as in the tapped-BBD example above, and get different emphasis, but without the time stagger.

On the other hand, cascaded allpass stages don't HAVE to be modulated by the same source or by the same amount.  So, for instance, it is theoretically possible (though I'd certainly never find the bench time to do it anywhere in the next decade or so) for the amount of modulation from a source to be staggered across the stages.  You have, no doubt recognized that most FET-based phasers have a fixed resistor in parallel with the drain and source to set a maximum resistance to ground.  Change that resistor across stages or pairs of stages, maybe add another small one in series between source and gnd, and you have stages that are modulated by different amounts and having different "starting points".  I'm sure there are many other ways to do it, but that's one.

This should, in principal, yield several simultaneously derivable outputs that produce non-overlapping changes in pitch-deviation.  I'll make up some numbers here.  Tap 1 after 2 stages yields 0-2 cents of shift, tap 2 after 4 stages yields 2-5 cents of shift, tap 3 yields 5-9, and so on.  Keep in mind that is all in the realm of the hypothetical.

Now, is one system any better than the other?  No.  Both are musically valid, though whether one is more listenable without fatigue than the other, I cannot say.  Certainly time-staggered pitch-shift ought to, in principle, give a better illusion of a multi-source ("chorus") signal.  The phase-shifter method ought to deliver a more parametrically controllable multi-vibrato.  Whether the possibility to directly control how much pitch-deviation is introduced within each tap should improve the apparent distinctiveness of each tap swhen mixed down, the simultaneity would, on paper, reduce the illusion of multiple sources.

All of this is very tentative, but nevertheless well worth experimenting with.  The easiest way to determine how true it is would be if someone out there with a multi-VCO modular synth and bank of trigger-delays could do the experiment.

[Fp-www.Tonepad.com]

A test of this could be made with pluggins on cooledit or other audio software, just to have an idea on how it'll sound.

Fp

[DiyFreaque]

Let's say, however, that the various taps produce different amounts of pitch deviation (longer taps producing greater pitch deviation), plus the time stagger introduced by the difference in tap points (stagger = #stages at tap point B minus #stages at tap point A times clock rate).  The pitch deviation you hear *most*, however, can still be altered, by adjusting the relative amplitude of each tap at the mixing stage.  Fade taps 4 through 6 to the background, and subtler pitch shift should dominate.  Reverse that mix, and more robust pitch shift should be heard.

With a BBD, the intensity of the modulation (IE, the perceived range of pitch deviation) is determined by how much delay is introduced in the modulation and the speed of modulation.  A large delay range produces a more dramatic pitch shift than a small delay range for a given delay modulation depth and rate.  The higher modulation rate and rate, the more intense the effect.  In this case we're looking at vibrato, which is usually around a 6.5 Hz modulation rate.  A large delay range will render an apparent pitch shift much more readily than a shorter delay range, because the perceived pitch shift is much greater for a given modulation index. 

So, for the MN3011 the worst case example would be the following, using a modulation intensity of +/- 5 kHz clock deviation from a center point of 15 kHz clock frequency:


Tap 1 = 396 Stages

10 kHz = 19.8 ms
20 kHz = 9.9 ms

Deviation range is 9.9 ms
Modulation +/- 4.95 ms from center point.

Tap 6 = 3328 Stages

10 kHz = 166.4 ms
20 kHz = 83.2 ms

Deviation range is 83.2 ms
Modulation = +/- 41.6 ms from center point.

So, from tap 1 to tap 6, there's nearly a tenfold increase in modulation index, which is a lot when it comes to perceived frequency deviation.

Obviously at tap 6, 10 kHz to 20 kHz clock range is going to give a lotta slapback.  If you cranked the initial clock frequency to eliminate the slapback, tap 6's vibrato would still be apparent, but then tap 1's would probably be such a shallow range as to be imperceptible, or barely perceptible, vibrato-wise.  Probably more interesting in this case would be the flanging aspects of it all.  We're basically looking at an STD-1 here, only without the inclusion of the dry signal in the final mix.  In any event, I think the difference between the tap extremes would result in too wide of a spread of effect - IE, fading tap 1 out and tap 6 in to alter the level effect would actually result in an altering of the perceived effect itself - say go from a nice vibrato to a more obnoxious, heavily bent sound .  In other words, it depends on what one means by more robust  .  Fading through the first two or three taps perhaps would be more of a variation of the vibrato intensity itself.

All in all , using all the taps, it's gonna sound cool, but perhaps not in the way expected.

Ok, definitely worth trying then. But is it a way to get jet-flanging? Or is it better to use a set-delay BBD with a modulated delay so you raise the delay ratio. (like in MN3207 2.5msec to 50msec, but with a fixed one at 3msec for example and a modulated one at 3.5msec to 50msec, you would get real good flanging, no (resulting in 0.5msec to 47msec)?

I think you can get the same jet sound whichever way you apply it - as long as the delay times of the two BBD's 'cross' at some point.  I think what will differ is in what shape you will want the modulating waveform to be.  With a fixed delay and a moving delay, the moving delay would probably sound best with a parabolic LFO.  With both delays moving, you could probably get away with a linear triangle waveform.  Note that with both delay lines moving in complementary directions, your perceived flange sweep will be double than that of only one delay line moving using the same modulation frequency.

[DiyFreaque]

Note that with both delay lines moving in complementary directions, your perceived flange sweep will be double than that of only one delay line moving using the same modulation frequency.

I should qualify that by stating "if you sweep each BBD through its entire range, which is equal to the range of the opposite BBD".  IE, until they meet in 'center field, the flange sweep is sweeping up.  After center field, and they pass each other, the flange sweep is sweeping down - one half cycle of the LFO has created an up/down sweep.

Dave - did you get my reply?

Chario,
Skawt

[puretube]

just a little food for thought
for shifting (phase...) into 2 different directions
the other way... :
http://www.pat2pdf.org/patents/pat2624041.pdf

[Mark Hammer]

Scott,

Thanks for doing the math and answering my question.  My hunch was what you eventually demonstrated (which was initially prompted my interest in multi-vibrato), but at the last moemtn, in the absence of the math, I started wonderinf whether the taps wouldn't just shift the pitch by the same amount, just staggered in time.  Clearly, that doesn't happen.

The substantial discrepancy in pitch-deviation between earlier and later taps suggests a few things.  First, it suggests that an MN3214 might be a more suitable chip than an MN3011 for such an application.  Second, it suggests that allpass stages might be a more suitable method fo multi-vibrato than BBDs.  Certainly the tapped-BBD presents a more compact and cost-effective solution for multi-vibrato, but one is stuck with the predetermined taps and their associated spacing.  Use of allpass stages allows you to cluster them more closely, producing less inter-tap discrepancy in range of pitch-deviation, and have as many taps as you feel like having.

(Incidentally, even numbers of allpass stages are needed to produce a notch.  But when you're primarily interested in pitch wobble, rather than notches, are even numbers a requirement, or can 3 allpass stages be suitable for yielding pitch wobble?)

Those allpass taps might well sound terrific if staggered a bit in time via BBD, but even without time stagger, the issue of where your attention ought to be directed at this moment or that is less of a problem when discrepant pitch-deviations are not THAT discrepant.  Splitting your attention between pitch-jiggle and pitch-roller-coaster is hard to do.

[DiyFreaque]

Hi Mark,

I still think it would be worth it to wiggle an MN3011 around and see what you did come up with.  I've been planning on that since, what, last spring?  My projects have been sliding due to increased demands from work, home life, and an overactive project planner lobe I have buried somewhere in my ganglia.

Getting back to the MN3011 - if one did ramp up the clock and give the longer taps decent but not overactive vibrato, I still wonder if the shorter taps would still contribute something to it, vibrato-wise.  Chorus and flanging is a no brainer, absolutely yes, but vibrato.  Hmmmm.....

All pass stages may be the way to go, though.  I've still got my 12 stager situated on a breadboard.  Ah, but this weekend is to be dedicated to Tiger Scout popcorn sales, and I've got a project for a friend on the books that takes supreme importance, which hopefully some Thanksgiving vacation time will help get going.

Take care,
Scott

[puretube]

1 stage can wobble, also...

[Mark Hammer]

Enough to be audible?  If so, that could be the basis of a ridiculously simple vibrato circuit.  The Phase45/90 uses a 1-op-amp LFO.  That plus a single FET-based allpass stage, a FET input buffer, and that's pretty much it.  A dual op-amp, 2 FETs, and a couple of passive components.  Kind of the Bazz Fuss of vibrato.

[puretube]

some sources say:
phase-shift = frequency-shift;

the thing with allpass-shifters is their frequency-dependancy...

so you can get 180° shift out of 1 stage - however only for a certain
(limited) frequency range;
that`s why you want more stages, to shift all frequencies by at least this amount
(or more);
my everloved/mentioned Dome staggers various continuous ranges throughout the wanted bandwidth
to be shifted by at least that amount...
(to get the whole st*ff moved...)

[puretube]

btw: although this doesn`t neccessarily fit into the topic of this thread,
Mark being the starter of it, will forgive me (soon),
it`s about time to mention once again
that the expression "chorus" in the "FX-scene"
has not been connected to "delay" at all,
when it came up;
it was rather related to "pitch/frequency-altering",
like the other frequently used ancient expression: "celeste",
which used to be used for the mentioned (slower )pitch-alterations
in combination with a dry signal,
(nowadays commonly known as "Phasing")...

[Mark Hammer]

Correct.  the Uni-Vibe's "chorus" setting is no delay-based chorus at all, but a phase-shift effect of a certain kind/flavour.

[amz-fx]

Mark,

Along these lines, I built a circuit that had four filters from the Quadafuzz that were run to 4 Small Stone phasers and then mixed back togther for the output.  This was about 20 years ago and all I can remember about it is that I was disappointed in the sound and it turned out to be a lot of work for not much in the way of results.

regards, Jack

[donald stringer]

I cant shed any light on how to do what you want mark. But I can say there is something to be said for  a subtle vibrato and delay mix. I have an rp-300 on which you can obtain  this sort of preset. Also on my crate dx212 a very similiar response can be had utilizing there vibrato and playing with the tap tempo. One interesting thing is the magic of the sound dissappears if it goes beyond the point of being subtle. So what I am saying is less is more in this case. To much and it just degenerates into sounding like another lousy factory preset. Good luck and I hope you figure it out.

[A.S.P.]

information lost...

[puretube]

nice reading for those, who always wanted to know more...
http://www.pat2pdf.org/patents/pat2254284.pdf
http://www.pat2pdf.org/patents/pat2276389.pdf
http://www.pat2pdf.org/patents/pat2382413.pdf
http://www.pat2pdf.org/patents/pat2830481.pdf
http://www.pat2pdf.org/patents/pat2905040.pdf

[David]

All I can say is... WOW!

How come I never heard of this Hanert dude before?  His name should be mentioned in the same breath as Messrs. Hammond and Leslie!

[puretube]

Hanert was the sound behind Hammond...