Barberpole Through-Zero Flanging

[DrAlx]

This product recently appeared...

http://www.mrblackpedals.com/products/shepards-end

I remember Stephen Giles suggesting barberpole TZF before,  and I also remember saying that I could see how a barberpole flanger could work, but not with through-zero too.

My thinking was that you would implement the barberpole effect by mixing together several flanger sounds.
All flangers would have the same rate sweep but be at different stages of the sweep. 
Each flanger would be gradually faded into the mix (starting as the the bottom of its upward sweep) and gradually faded out of the mix as it reaches the top of its upward sweep.  So the whole effect would be a never-ending upward flanger sweep that never actually reaches the top.
Therefore you could never get a true zero point (cos you would always have to fade out a flanger as it approached its zero point).
So I am intrigued about what this pedal does.

The first short clip on the above link sounds like a set upward flanger sweeps to me, almost glued one after the other.  It doesn't have that "constantly sweeping upwards but never getting there" effect that I was expecting, but that might just be down to the clip.  Hopefully a better demo will be posted.

[DougH]

I'm not hearing the sweep very well in either one of those clips. Flanger demos like that should use wide-band material like a mix, instead of the typical guitar/bass noodling. A sustained sound with a wide freq range will really show you what the sweep is doing.

[Mark Hammer]

The Wave control appears to provide for continuous adjustment of the skew of a triangle wave, from a symmetrical up/down sweep, to one where there is ONLY up, or only down.  What makes a barberpole a barberpole is that there is never any point where there is an identifiable start-point to a sweep.  If the LFO was a quadrature type, with variable skew of two synced (but staggered) outputs, such that one BBD was being swept upwards while the other was ending its sweep and coming back to the starting point, that could work.

Not sure if that's what I'm hearing in the samples, though.

[StephenGiles]

I'm sure Ton has played around with this - I haven't seen him lurking around here for a while! Pity the samples are less than useless, simple sustained chords would have been much better. Why is it that these pedal demonstrators never demo the pedal, just their flash playing???

[StephenGiles]

Now if it sounded like this:
https://www.youtube.com/watch?v=BzNzgsAE4F0

we'd be on to something!

[armdnrdy]

Now if it sounded like this:
https://www.youtube.com/watch?v=BzNzgsAE4F0

we'd be on to something!

Okay....who's going to engineer the circuit to do this! Very cool!

[DrAlx]

Now if it sounded like this:
https://www.youtube.com/watch?v=BzNzgsAE4F0

we'd be on to something!

Okay....who's going to engineer the circuit to do this! Very cool!

Ton already has. He posted this a while back on another thread ...
http://youtu.be/Jf6WpL_e4NI

[StephenGiles]

The Wave control appears to provide for continuous adjustment of the skew of a triangle wave, from a symmetrical up/down sweep, to one where there is ONLY up, or only down.  What makes a barberpole a barberpole is that there is never any point where there is an identifiable start-point to a sweep.  If the LFO was a quadrature type, with variable skew of two synced (but staggered) outputs, such that one BBD was being swept upwards while the other was ending its sweep and coming back to the starting point, that could work.

Not sure if that's what I'm hearing in the samples, though.

Sweep generator 1 (for BBD1) is say a triangle quadrature LFO at 0 degrees. Consider an "Adaptive Sweep Detector" applied to the LFO CV - one which is configured to output a suitable CV to a VCA for muting BBD1 audio at the end of its upward sweep, through its downward sweep, and then opening the VCA again at a point just after the start of its upward sweep.

Sweep generator 2 (for BBD2) lags Sweep Generator 1 by an appropriate amount, which is applied to Adaptive Sweep Detector 2 in the same way, thus opening and closing a VCA on BBD2 output, but at different times. The lag is set within the quadrature to control the timing gap between heard sweeps of the BBD outputs.

I wonder if the Flanger Hoax could be modofied to do this?  Ton where are you??

[Ice-9]

It will be DSP Fv-1 based.

[Mark Hammer]

What makes you say that?

[StephenGiles]

From my bed  The word I was looking for is "lag". now amended my previous post!

I think that the synth boys over at electro-music.com use a frequency shifter for barberpole phasing.

[Ice-9]

What makes you say that?

Having built many FV-1 based pedals myself, the DSP has a sound of it's own that is quite recognizable, and can be spotted a mile off, then there is the fact that a lot of the pedals in his great range are based on this chip. I am talking about the pedal demo in by OP not the you tube effect.

[StephenGiles]

I'm sure that the you tube effect was processing a synthesiser.

I am of the opinion that my idea would need a substantial amount of circuitry which is unlikely to fit in your favourite tiny box - so bring out your racks !!

Perhaps my "adaptive sweep detector" could be achieved with a combination of various cmos chips - I can certainly see a 4016 in there for switching. You could hit lucky with a patent trawl, I can't be the first to think of this

Could synthesiser gate signal technology be borrowed? You press a key down (event 1) which generates a gate signal, staying on until you release the key (event 2). So our event 1 is the LFO reaching the end of it's upward sweep, and event 2 is after its downward sweep and just after the start of its upward sweep again. Are we looking at a type of "window comparator" perhaps?

[Ice-9]

I'm sure that the you tube effect was processing a synthesiser.

I am of the opinion that my idea would need a substantial amount of circuitry which is unlikely to fit in your favourite tiny box - so bring out your racks !!

Perhaps my "adaptive sweep detector" could be achieved with a combination of various cmos chips - I can certainly see a 4016 in there for switching. You could hit lucky with a patent trawl, I can't be the first to think of this

Could synthesiser gate signal technology be borrowed? You press a key down (event 1) which generates a gate signal, staying on until you release the key (event 2). So our event 1 is the LFO reaching the end of it's upward sweep, and event 2 is after its downward sweep and just after the start of its upward sweep again. Are we looking at a type of "window comparator" perhaps?

No doubt the youtube effect was processing a synth,  My observation was about the pedal in the original first post and not the youtube link. 

[Mark Hammer]

What makes you say that?

Having built many FV-1 based pedals myself, the DSP has a sound of it's own that is quite recognizable, and can be spotted a mile off, then there is the fact that a lot of the pedals in his great range are based on this chip. I am talking about the pedal demo in by OP not the you tube effect.

Fair enough.  Not quite as familiar with that chip myself, apart from the various pedals that use it for stock effects.  So there was nothing about it that said "Ah, one of those" to me.

Once upon a time, one could gauge the technological engine underlying something by how big the chassis was.  More complex effect = more complex circuit = more chips = more real estate.  I guess, with SMD, tiny pots, and VLSI chips like the FV-1, judging circuitry on the basis of size is a fool's game. 

[amz-fx]

An article about Shepard Functions from Paia:

https://www.paia.com/talk/download/file.php?id=166

regards, Jack

[DrAlx]

I've done an "animation" of the frequency response of a simple barberpole flanger as it sweeps upwards.

http://1drv.ms/1TGWDZO

Each slide shows the frequency response plot of the flanger notches between 0 and 10 kHz. 
If you run through the slides quickly enough you will see how the flanger notches sweep upward in a never-ending repeating pattern. (Repeats every 10 pictures).


I calculated all the pictures using Excel.  This is the overall design:

The barberpole effect is produced by mixing together 2 flanger outputs.
Both flangers sweep upwards from 1ms delay to 0.2 ms delay over some fixed time period.
When the delay for a flanger reaches 0.2 ms then that flanger will jump back to 1ms delay and start another sweep towards 0.2ms delay.

The 2 flanger sweeps are staggered, so that when one flanger is at the midpoint of its sweep (i.e. has delay time of 0.6 ms) then the other flanger has just reached the end of its sweep (0.2ms delay) and is jumping back to the start (1ms delay).

The two flangers outputs are mixed together in a time varying way as follows:
The gain for a flanger varies linearly according to where it is in its sweep, with the middle of the sweep (i.e 0.6ms delay) getting a gain of 1 (no attenuation) and the start/end points (delay 0.2ms and 1ms) getting a gain of 0 (i.e. complete attenuation).


EDIT:  One thing to notice from the pictures.  Although the peaks and notches always sweep upwards, the total number of them varies.
e.g. there are more peaks and notches in the 5th picture compared to the 1st.
Therefore the total number of peaks and notches will go up and down, even though they only ever sweep upwards.
I am not sure what this will sound like, but I am guessing that for a slow sweep you are more likely to notice the direction that the notches are moving rather than the total number of them.

[DrAlx]

In case anyone is interested the spreadsheet for creating the pictures is shared here...

http://1drv.ms/1ObWDx1

Hit the "Edit in Browser" button to change the three numbers in red, and it will redraw the graph.

The maximum and minimum delay in milliseconds are the min and max delay that each flanger sweeps between.
The "cycle position" is a number from 0 to 100.  As you increase the cycle position, the flanger notches will move right.  The picture for position 100 will be the same as the picture for position 0 since the cycle repeats every 100.

[DougH]

Now if it sounded like this:
https://www.youtube.com/watch?v=BzNzgsAE4F0

we'd be on to something!

Yes, this is what I was expecting. Yet I get fooled almost every time.

[StephenGiles]

I am not interested in dsp, only an analog solution.

Another idea -

Same BBD 1 and BBD 2 with VCA 1 and VCA 2 on respective outputs.

LFO 1 is a triangle oscillator, sharing a rate pot with an identical LFO 2. At rest, assume LFO output is low. When power is applied, LFO 1 starts to sweep high which is detected by control circuitry at the point where LFO 2 is required to start, in order to send appropriate gate/pulse or whatever to energise it. This needs to be a one off event so that a constant lag is maintained between the two LFOs.

LFO1 would control BBD1 and LFO 2 would control BBD2 as in normal flangers.

Clever bit - LFO 1 output might also control VCA 2 with LFO 2 controlling VCA 1, in such a way that all of the falling sweep and the first part of the rising sweep from each BBD are attenuated.