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.
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.
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.
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???
Now if it sounded like this:
https://www.youtube.com/watch?v=BzNzgsAE4F0
we'd be on to something!
Quote from: StephenGiles on July 16, 2015, 03:39:48 PM
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!
Quote from: armdnrdy on July 16, 2015, 03:45:41 PM
Quote from: StephenGiles on July 16, 2015, 03:39:48 PM
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
Quote from: Mark Hammer on July 16, 2015, 10:02:06 AM
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??
It will be DSP Fv-1 based.
What makes you say that?
From my bed :icon_rolleyes: :icon_rolleyes: 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.
Quote from: Mark Hammer on July 16, 2015, 10:14:09 PM
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.
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 :icon_biggrin:
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?
Quote from: StephenGiles on July 17, 2015, 06:45:02 AM
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 :icon_biggrin:
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. :icon_wink:
Quote from: Ice-9 on July 17, 2015, 05:20:42 AM
Quote from: Mark Hammer on July 16, 2015, 10:14:09 PM
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. :icon_smile:
An article about Shepard Functions from Paia:
https://www.paia.com/talk/download/file.php?id=166
regards, Jack
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.
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.
Quote from: StephenGiles on July 16, 2015, 03:39:48 PM
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.
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.
I suggested a way of taking LFO sweep signals and rectifying them so they could be reused as the VCA mix controls here ...
http://www.diystompboxes.com/smfforum/index.php?topic=107739.msg979927#msg979927
but that was using 4 flangers not 2.
If you want to use just 2 flangers, then the delay CV for each flanger's BBD needs to be a saw-tooth (lets say repeatedly increasing from 1V to 5V).
I think it would be quite easy to convert that to a secondary control voltage for that flanger's VCA.
The problem is to find a nice analogue way of having the two sawtooth waveforms for the two flangers "delayed" with respect to each other.
Quote from: DrAlx on July 17, 2015, 02:46:56 PM
I suggested a way of taking LFO sweep signals and rectifying them so they could be reused as the VCA mix controls here ...
http://www.diystompboxes.com/smfforum/index.php?topic=107739.msg979927#msg979927
but that was using 4 flangers not 2.
If you want to use just 2 flangers, then the delay CV for each flanger's BBD needs to be a saw-tooth (lets say repeatedly increasing from 1V to 5V).
I think it would be quite easy to convert that to a secondary control voltage for that flanger's VCA.
The problem is to find a nice analogue way of having the two sawtooth waveforms for the two flangers "delayed" with respect to each other.
Yes, and the components of each LFO would need to be closely matched to ensure constant speed. Is there a dedicated dual LFO chip?
Quote from: DrAlx on July 17, 2015, 02:46:56 PM
If you want to use just 2 flangers, then the delay CV for each flanger's BBD needs to be a saw-tooth (lets say repeatedly increasing from 1V to 5V).
A 4013-based ramp oscillator should be able to do this, right?
Quote
The problem is to find a nice analogue way of having the two sawtooth waveforms for the two flangers "delayed" with respect to each other.
Send each ramp output into a comparator and send the comparator output into the CLOCK pin of the other 4013 ramp. When one ramp reaches the trigger point of the comparator, it will restart the other ramp. That way each ramp is reset from high to low voltage when the other ramp is at the halfway point.
Buchla synthesizers makes a barberpole phaser.
https://www.youtube.com/watch?v=lWHtIfUJ2gg (https://www.youtube.com/watch?v=lWHtIfUJ2gg)
I recall seeing an old hobby project - 'infinite flanger' or 'infinite phaser' - may have been PAIA Related. I'll dig around in the archives at home later, I'm wondering if the 'infinite' is a barberpole/shephards tone reference.
Strategy
Quote
Send each ramp output into a comparator and send the comparator output into the CLOCK pin of the other 4013 ramp. When one ramp reaches the trigger point of the comparator, it will restart the other ramp. That way each ramp is reset from high to low voltage when the other ramp is at the halfway point.
Comparator measuring one ramp and causing it to reset the other (and vice versa) sounds like it will work, but don't you still need to match the slopes of the two ramps?
e.g. Lets say Ramp1 voltage increases at a rate of 1 V/s (volt per second) but Ramp2 increases at a rate of 2 V/s.
Lets assume both voltages start off at 0 at switch on, and we set a reset trigger level of 4V.
Ramp2 reaches 4V first (at t = 2 seconds) and causes Ramp1 to reset to 0.
Then 4 seconds later at t = 6 seconds, Ramp1 reaches 4V and causes Ramp2 (which is now at 12V) to reset to 0.
Then 2 seconds later at t = 8 seconds, Ramp2 reaches 4V and causes Ramp1 (which is now at 6V) to reset to zero.
So overall we have Ramp1 going from 0 to 6V, and Ramp2 going from 0 to 12V, and the threshold of both ramps (at 4V) is not at the centre of either ramp. (Which translates into the two ramps not being correctly delayed with respect to each other).
So I think we need to be match the slopes of the two ramps for this triggering scheme to work properly.
I can't think of a way of matching the slopes of the two ramps (and being able to keep those slopes matched as we turn the "Rate" pot).
The rate of each 4013 ramp oscillator can be controlled with a single R-C combination, at least if I'm imagining that circuit right. A dual gang pot can change two of them at once, keeping them matched closely enough for this purpose I would think. You're right that they need to be the same speed (at least roughly), but if you only need two ramps I don't think it's a problem.
It's important for the comparator threshold voltage to be no more than half the 4013 supply voltage, though, otherwise one ramp will get stuck at its max voltage for a bit before resetting.
What`s that mysterious 4013 ramp oscillator?
Here's a page with info: http://www.edn.com/design/analog/4313895/Turn-a-set-reset-latch-into-an-astable-monostable-multivibrator
(http://m.eet.com/media/1126484/11429-figure_2.pdf)
This is a generalized monostable circuit that generates square pulses of a fixed width. Note that if you take the output from the R pin, you get not a square pulse when Q goes high, but a gradually rising voltage as the cap is charged up, with the rise time determined by the R1C1 time constant. When pin 1 changes to a low state, the cap is discharged quickly through D1.
Also, as shown it's not specific to the 4013, or to the needs we're discussing. We'd want the SET pin high, the DATA and RESET pins grounded, and R1/D1/C1 not connected to RESET. The CLOCK pin is triggered by the comparator, which is triggered by the opposite ramp. That way, as the chip powers up in the SET state, the cap begins charging. When one ramp reaches the comparator trigger point, it causes the flipflop to switch states momentarily, discharging the cap through the diode, then the process starts again.
I actually don't know how smooth of a ramp this would give. It seems to me that as the cap voltage rises, the rate of change would slow due to less current through R1. Also, the fall of the ramp depends on how fast the cap can discharge through D1/R1, so it might need a short time delay before it begins rising again, but that could be done easily by using an R/C combination on the SET pin.
It's late, so someone please check everything I just said. I think it can be made to operate, though.
It occurred to me over a late breakfast just now, (and I was in trouble of course for losing track of what my wife was saying to me :icon_rolleyes: :icon_rolleyes:) that the Barberpole effect would mainly tend to be used with a slow LFO rate - because it sounds dreadful at faster rates (ducks for cover!). I don't know if that would affect any design considerations.
I'm sure I've seen a synth circuit, perhaps even a modded one which perform this trick. There may be something useful in the H&SR Dual Gate control circuitry
https://www.dropbox.com/sh/2aedsoafmaa3bc7/AACiigi5aVYTjrPP1ybQMO_oa?dl=0
- it's always worth another read, there all manner of clever triggering, rising & falling voltages and electronic switching going on in there.
What about the LFO in a Standard Electric Mistress, could that be adapted to trip a second identical one at the right time?
Quote from: StephenGiles on July 18, 2015, 09:00:19 AM
What about the LFO in a Standard Electric Mistress, could that be adapted to trip a second identical one at the right time?
Maybe, but it's not a ramp, in the sense we're talking about. It would fall at the same speed that it rises, so it wouldn't be very useful for the barber pole effect without modification.
Anyone know if this type of oscillator can easily be converted to a ramp? I'm wondering if a diode in parallel with the resistance between opamp stages would do it.
Quite a few years back Gez (remember him) made a clever circuit that gave you dual LFOs locked at the same speed where you could vary the phase between them, that would do what you need for barber pole flanging. It used a load of CMOS chips and some other stuff. I'll see if I can find the thread but there's always the risk that the schematics have been lost in the mists of time.
Failing that I'd be very surprised if the DIY synth guys don't have something suitable.
Well that was easier than I thought and it looks like all the info is still there http://www.diystompboxes.com/smfforum/index.php?topic=72676.120 (http://www.diystompboxes.com/smfforum/index.php?topic=72676.120)
It was to create a sine LFO but by tweaking the 4051 stages you could do saws or triangles.
Today, i'd go for a hybrid solution: digitally generated waveforms, bunch of DACs, some filtering, level/amplitude adjustment to drive whatever you want to use in the barberpole FX.
A 10$ dev kit like this one:
http://www.cypress.com/documentation/development-kitsboards/cy8ckit-059-psoc-5lp-prototyping-kit
would be able to generate enough perfectly synced, phase shifted waveforms (DDS with multiple outputs) using its PWM blocks or built DACs.
Example:
Let's say we want an LFO with 8 pairs of outputs, 1st ramp-up to control the delay line, 2nd triangle to control the VCA of the channel.
I've made simple hardware config project to test if it works (compiles):
(http://i236.photobucket.com/albums/ff176/314_tr/Schematics/hdw_schm_zpsclzxx1yh.png)
The ADC reads the pots and supplies parameter values for the DDS. 8 two channel PWM blocks are used as DA converters, working at 12bit/about 20kHz in 0-5V range. A typical DDS algorithm is perfect for generating multiple synced waveforms, you just use as many read pointers with offsets as you like. To drive a BBD it would be even better to generate a clock signals in opposite phase to spare additional VCOs for each path. No problem for a 80MHz Arm MCU. Yeah, it's probably an overkill, but hey it's 10 bucks, the chip itself costs more in single quantities as this dev kit.
I think it would be the most compact and cost effective solution for a serious barberpole effect device. That PSoC has a current output DACs, too (8bit, though). Something that could drive a VCA or an OTA directly.
Quote from: free electron on July 18, 2015, 03:52:45 PM
Today, i'd go for a hybrid solution: digitally generated waveforms, bunch of DACs, some filtering, level/amplitude adjustment to drive whatever you want to use in the barberpole FX.
A 10$ dev kit like this one:
http://www.cypress.com/documentation/development-kitsboards/cy8ckit-059-psoc-5lp-prototyping-kit
would be able to generate enough perfectly synced, phase shifted waveforms (DDS with multiple outputs) using its PWM blocks or built DACs.
Example:
Let's say we want an LFO with 8 pairs of outputs, 1st ramp-up to control the delay line, 2nd triangle to control the VCA of the channel.
I've made simple hardware config project to test if it works (compiles):
(http://i236.photobucket.com/albums/ff176/314_tr/Schematics/hdw_schm_zpsclzxx1yh.png)
The ADC reads the pots and supplies parameter values for the DDS. 8 two channel PWM blocks are used as DA converters, working at 12bit/about 20kHz in 0-5V range. A typical DDS algorithm is perfect for generating multiple synced waveforms, you just use as many read pointers with offsets as you like. To drive a BBD it would be even better to generate a clock signals in opposite phase to spare additional VCOs for each path. No problem for a 80MHz Arm MCU. Yeah, it's probably an overkill, but hey it's 10 bucks, the chip itself costs more in single quantities as this dev kit.
I think it would be the most compact and cost effective solution for a serious barberpole effect device. That PSoC has a current output DACs, too (8bit, though). Something that could drive a VCA or an OTA directly.
I'm sure you are right, but I was under the impression that an analog solution was being sought :icon_biggrin:. Compactness and smallness of box is not a consideration, certainly not to me anyway :icon_biggrin:!
https://www.youtube.com/watch?v=d35o1G1fMr8
This is the sound!
Quote from: StephenGiles on July 18, 2015, 04:23:34 PM
https://www.youtube.com/watch?v=d35o1G1fMr8
This is the sound!
Yes That was the link I found a yesterday and though, wow.
Quote from: StephenGiles on July 18, 2015, 04:14:57 PM
I'm sure you are right, but I was under the impression that an analog solution was being sought :icon_biggrin:. Compactness and smallness of box is not a consideration, certainly not to me anyway :icon_biggrin:!
Oh, i just wanted to throw in another idea.
You said no dsp only. The output of the circuit i proposed is an analog control voltage. Which, in case of a BBD based flanger, in the end is converted into a digital one anyway (clocks).
Ah yes I see now :icon_biggrin: sorry, my mistake!
I think at the end of the day it will be a combination of various technologies, and if it isn't - then we haven't reached the end!
Thinking about Keppy's suggestion. Not quite sure I understand how the capacitor starts recharging after it has been discharged. As long as the discharge diode is switched on the cap can't be recharged. So the discharge diode needs to stay conducting just long enough to empty the cap and no longer. Problem is that the comparator that switches on the discharge diode leaves it switched on for 25% of the overall cycle (unless I've understood things wrong). Also the cap voltage doesn't charge linearly as pointed out by Keppy.
So was thinking about another approach:
1) Start off with a (low frequency) square wave with 50% duty cycle. There are lots of ways to generate this.
I'll assume that this square wave comes from the Q output of a flipflop, and so we have inverse square wave available at the other flipflop output (Q*).
2) The rising edges of Q and Q* are interleaved evenly in time (i.e. rising edge Q, rising edge Q*, rising edge Q, rising edge Q*, ...).
3) Now feed Q into an edge-triggered one-shot multivibrator whose job is to take the rising edge on Q and convert it to a short duration output notch. See waveforms here.
http://www.electroschematics.com/11032/edge-triggered-555-monostable-multivibrator/
We can choose component values to decide the duration of the output notch, and we'll use that output notch to control when a discharge diode is switched on.
Similarly Q* drives its own edge-tiggered one-shot multivibrator that controls a second discharge diode.
Edit: A CD4528 dual multivibrator chip would do the trick with minimal extra components. (Just one R and one C for each one-shot to set set the notch width).
4) To get the linearly rising control voltages, take two capacitors and charge them up using constant current sources (e.g. put each cap on the collector arm of a PNP transistor like in the deluxe electric mistress VCO). The cap voltage is the ramp voltage we are trying to generate.
Hook each cap to its own discharge diode, and each diode is controlled by its own one-shot.
Thinks to note:
a)Overall flanger rate is governed by the rate of the initial square wave.
b)You can never fully discharge the cap (because of the voltage drop across the diode). Shouldn't be a big deal in practice.
c)The current sources cause the cap voltages to increase mostly linearly but there is also a rapid initial charging of each capacitor due to diode reverse recovery current when the discharge diodes switches off. I think this will not be a major effect if caps are suitably large.
d) Flanger sweep range is governed by the current sources that charge the caps. Not sure of the best way to keep those sources variable yet matched. Current mirrors?
I refer you to the H&SR Dual Gate linked above for capacitor discharge and recharge circuitry!
Quote from: DrAlx on July 19, 2015, 09:40:19 AM
Thinking about Keppy's suggestion. Not quite sure I understand how the capacitor starts recharging after it has been discharged. As long as the discharge diode is switched on the cap can't be recharged. So the discharge diode needs to stay conducting just long enough to empty the cap and no longer. Problem is that the comparator that switches on the discharge diode leaves it switched on for 25% of the overall cycle (unless I've understood things wrong). Also the cap voltage doesn't charge linearly as pointed out by Keppy.
That's why the comparator is hooked to the CLOCK pin. That pin is triggered by a sharply rising voltage that causes the state of the DATA pin to be transferred to Q. I had been thinking the SET pin would then retake priority after the pulse and begin charging the cap. Upon checking the datasheet, I think I got that wrong, not because the SET pin wouldn't take over after the clock pulse, but because the SET pin would cause the clock pulse to be ignored in the first place and the cap would never discharge. So yeah, I don't think my idea will work. Thanks for checking me.
You seem to be thinking along the same lines as me, only with more clarity. :) Edge-triggered one-shots with the ramp voltages taken from the timing caps seem like a workable, non-microcontroller way of generating offset ramp voltages from a single LFO.
An advantage of generating the ramps indirectly (i.e. by having a square wave set the overall timing, rather than having the "ramp caps" set the timing) is that if you generate the initial square wave using the common triangle/square wave LFO, then the triangle wave gives you the mix control signal for the VCA.
See waveforms in pic here:
http://1drv.ms/1HEqEEf
I've assumed the one-shots as being triggered on the downward slopes of the square waves and this gives the notches that control the discharge diodes for the ramp caps.
The peaks of the triangle wave correspond to the middle of the ramps.
Something else just occurred to me (and should have been obvious from the start).
For a barberpole flanger based on 2 BBDs as described above, you only need a single VCA and single triangle wave control signal for the mixing.
Assuming the VCA gives a gain factor "G" that varies from 0 to 1, then you can mix things by taking a simple 2-input op-amp adder circuit with equal mix resistors.
Input 1: FlangerA
Input 2: ( FlangerB - FlangerA ) * G
So when G is zero we get all FlangerA at the output and when G is 1 we get all Flanger B.
A bit of thought shows that you don't need to pre-create the flanger sounds before mixing them.
Breaking each flanger sound down into its component Clean and Delayed parts...
FlangerA = Clean + DelayA
FlangerB = Clean + DelayB
and we can write
(FlangerB - FlangerA) * G = (DelayB - DelayA) * G
Therefore instead of having a 2-input op-amp adder, we can use a 3-input adder (with equal mix resistors) as follows
Input 1: Clean
Input 2: DelayA
Input 3: (DelayB - DelayA) * G
So the single VCA just needs to operate on the difference between the two delayed signals.
As before, we get the FlangerA sound when G is zero and the FlangerB sound when G is 1.
I LTspiced some stuff.
I think you can get both ramp voltages as well as a control voltage for the VCA with a single quad op-amp (LM324), a dual multi-vibrator (CD4528), and a dual analogue switch.
http://1drv.ms/1DqIpTk
As I pointed out above, a single triangle wave is all that is needed for the mix control, and a triangle wave with a trough in the middle of ramp can be made to work just as well as one with a peak in the middle of each ramp.
I took a regular square/triangle LFO using an LM324.
I couldn't find a model for the CD4528 one-shot multivibrator so substituted something else that gives a short duration pulse on every rising edge of the square wave from the LFO. (The other half of a CD4528 would be wired to give short pulses on each falling edge of the square wave).
A linear ramp voltage can be produced using a simple integrator, and it should be clear that when we use two of these to give two ramps we can match the ramp gradients by trimming the R values.
I haven't used an analogue switch before, but I've assumed that the one-shot can be used to close an analogue switch to reset the cap.
EDIT: In case anyone is wondering why I have modelled the op-amps with a negative supply set to Vee = 0.65V, it is because I found that a real world LM324 with 0V at the negative supply pin actually swings no lower than 0.65V. I found the spice modelling works more accurately if you pretend the negative supply is 0.65V rather than 0V.
A better demo video clip has been posted on the original link.
http://www.mrblackpedals.com/products/shepards-end
The first 10 seconds shows the barberpole effect quite well (the rest of the video not so much).
It sounds to me like the sweep goes back down a bit after the zero point has been reached.
I am wondering if each component flanger (I reckon there are just 2 of them) is only faded out of the mix after its zero point has been passed?
That would make sense to me since if you fade it out AT the zero point then you won't hear the zero.
If I'm right it means not all the notches in the frequency response are moving upwards for the whole cycle.
I can't see any other way to get both barberpole and through-zero though.
Still sounds pretty good.
You can hear it at the end as well. The rate is just faster. You hear the flanging continuously "going up" but...you don't hear a downward sweep.
But...I agree...the beginning of the sound sample is a much clearer example.
Yes, the first 10 seconds is just the demo we need - but the rest is rubbish, a complete mess :icon_rolleyes: :icon_rolleyes:
Quote from: DrAlx on July 21, 2015, 02:18:20 PM
A better demo video clip has been posted on the original link.
http://www.mrblackpedals.com/products/shepards-end
The first 10 seconds shows the barberpole effect quite well (the rest of the video not so much).
It sounds to me like the sweep goes back down a bit after the zero point has been reached.
I am wondering if each component flanger (I reckon there are just 2 of them) is only faded out of the mix after its zero point has been passed?
That would make sense to me since if you fade it out AT the zero point then you won't hear the zero.
If I'm right it means not all the notches in the frequency response are moving upwards for the whole cycle.
I can't see any other way to get both barberpole and through-zero though.
Still sounds pretty good.
I would think that perceptible through-zero requires that there be somewhere to pass through
TO. IN other words, some time has to be spent on the other side of zero, in order for the zero-point to be detectable. Like yourself, I find it hard to imagine barberpole and TZF co-existing, at least in any way that can be clearly heard.
Quote from: DrAlx on July 21, 2015, 02:18:20 PM
It sounds to me like the sweep goes back down a bit after the zero point has been reached.
I am wondering if each component flanger (I reckon there are just 2 of them) is only faded out of the mix after its zero point has been passed?
That would make sense to me since if you fade it out AT the zero point then you won't hear the zero.
If I'm right it means not all the notches in the frequency response are moving upwards for the whole cycle.
I can't see any other way to get both barberpole and through-zero though.
Quote from: Mark Hammer on July 21, 2015, 03:11:22 PM
I would think that perceptible through-zero requires that there be somewhere to pass through TO. IN other words, some time has to be spent on the other side of zero, in order for the zero-point to be detectable. Like yourself, I find it hard to imagine barberpole and TZF co-existing, at least in any way that can be clearly heard.
Check out the documentation: http://www.mrblack.jackdeville.com/manuals/shepards-end-manual.pdf
The WAVE control goes from Upward Cycle (CCW) to Thru-Zero (center) to Downward Cycle (CW).
That makes it seem like it doesn't do Barberpole and TZF at the same time.
I'm guessing the WAVE control doesn't change the gradients of the two parts of a triangle wave, but rather changes the amount of upward time vs amount of downward time. e.g. there will be a setting near the end of that control that gives a long sweep (where delay goes from 7ms to 0ms) followed by a very short sweep in the opposite direction (e.g. where delay goes from 0ms to 0.2ms) before the whole cycle repeats. That would explain why I'm hearing the zero point near the end of the cycle but not at the very end.
Actually come to think of it, a much more plausible implementation is that the two ramped delays actually only ever go in one direction (e.g. always ramping upwards to give increasing delay) and for the WAVE pot to actually control a FIXED delay for the "clean" signal.
In other words, each of the 2 flanger sounds are not made by mixing a clean signal with a (ramped) delay,
but rather by mixing a fixed delay with a ramped delay.
See the three slides here...
http://1drv.ms/1g4HqDD
Quote from: DrAlx on July 22, 2015, 08:57:58 AM
Actually come to think of it, a much more plausible implementation is that the two ramped delays actually only ever go in one direction (e.g. always ramping upwards to give increasing delay) and for the WAVE pot to actually control a FIXED delay for the "clean" signal.
In other words, each of the 2 flanger sounds are not made by mixing a clean signal with a (ramped) delay,
but rather by mixing a fixed delay with a ramped delay.
See the three slides here...
http://1drv.ms/1g4HqDD
That makes sense.
This fascinating thread seems to have died a death when it was getting very interesting. :icon_cry:
Quote from: StephenGiles on August 08, 2015, 05:51:59 AM
This fascinating thread seems to have died a death when it was getting very interesting. :icon_cry:
I have a feeling that DrAlx hasn't given up on it. I would imagine that he's working diligently on a build. :)
Quote from: armdnrdy on August 08, 2015, 08:49:46 PM
Quote from: StephenGiles on August 08, 2015, 05:51:59 AM
This fascinating thread seems to have died a death when it was getting very interesting. :icon_cry:
I have a feeling that DrAlx hasn't given up on it. I would imagine that he's working diligently on a build. :)
Aha, I'll keep quiet then - back to the manual for my new Tascam DR-05!
U.S. pat. # 2846913 (https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCIQFjAAahUKEwiZjOLyrqvHAhWC2xoKHYRFAlg&url=http%3A%2F%2Fpatentimages.storage.googleapis.com%2Fpdfs%2FUS2846913.pdf&ei=wlXPVZmjJIK3a4SLicAF&usg=AFQjCNHM7aqzV9nkGWGIPehBUr4CLYRZfQ&bvm=bv.99804247,d.d2s)
:icon_eek:
(65 years ago...)
Any developments on all this ?
The link I posted no longer works. Here is the doc shared again.
https://1drv.ms/p/s!AvrH61utWEtEg3EMUPPypvZwGLUj?e=jTx4l8
If I was going to do this I would do it on the FV1 since I know how to code one now (I posted a DIY Tonewoodamp project on the forum).
It should actually be a no-brainer on the FV-1 because of the way that pitch-shifting is typically implemented on that chip.
http://www.spinsemi.com/Products/appnotes/spn1001/AN-0001.pdf (http://www.spinsemi.com/Products/appnotes/spn1001/AN-0001.pdf)
You achieve pitch-shifting on the FV-1 by taking two offset ramp waveforms (like in my document).
Each ramp sweeps though the delay line memory, reads it, and dumps it to the output. The faster the sweep, the bigger the pitch shift you get at the output.
You repeatedly fade between the two ramp outputs to avoid discontinuites at the ramp ends.
So at the beginning and at the end of a ramp's sweep, the output signal is faded to zero, and at the middle of the ramp's sweep the output signal is not faded at all. The end result is a pitch shifted signal but with a tremolo in the volume (due to the repeated fading between ramps).
All you need to do to get "barberpole flanging" is mix that pitch shifted signal with a (fixed) delayed version of the clean signal.
And to make it "barberpole TZF" you just need to choose the fixed delay appropriately. (i.e. read from the middle of the delay line).
See http://www.spinsemi.com/knowledge_base/effects.html (http://www.spinsemi.com/knowledge_base/effects.html) and you will even see it mentions barberpole flange.
Thanks for reposting.
I found this recently while working on a related project,
https://www.researchgate.net/publication/286861511_Barberpole_phasing_and_flanging_illusions
It shows the LFO and VCA waveforms. It also has a lot of details which you probably don't need to know if you use the FV-1 pitch shifter.