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Barberpole phaser


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6/23/1998 4:00 PM
Mark Hammer Barberpole phaser
One of the niftiest ideas in phasing is the late Harold Bode's "barber-pole phaser" (Harold was Buffalo-based inventor of the vocorder).  
 
If you've ever seen a barber-pole (yes, barbers still exist, frayed fishing mags, strops, harware-store calendars, and all), you are familiar with the illusion of stripes that seem to keep going up and up ad infinitum. The illusion relies on the staggered red, white and blue stripes that are "out-of-phase" with each other, such that when one coloured stripe "ends" at the top of the pole (from whatever vantage point you are looking at), there is another just on its way. As the pole turns, the stripes keep on coming and coming.  
 
Bode's idea was to have two independently-controlled phasors (and I'm not sure if they were in parallel or series, or if that even matters), driven by a quadrature oscillator (an LFO that generates several versions of the exact same waveform, each somewhat out of phase with the other; the general form is 90 degrees out of phase, but some are configured to generate 45, 90, 135, and 180 degree-out-of-phase versions of the waveform), in this case a sawtooth/ramp generator. The version of the waveform that "lags" (i.e., the one 90 degrees behind the other) would always be driving one phase-shift section in the direction that the other section had just finished going in. The end result is that the two phasers always seem to be endlessly going "up" (or down, depending on the waveform). I haven't actually heard it, but it's supposed to be a neat effect/illusion.  
 
The Barber-Pole Phaser actually WAS a commercial rack-mount product, and I saw ads for them in POLYPHONY magazine, circa 1980. The knobs alone would bankrupt most DIY-builders. This is NOT something you can run off of a 9-volt battery or stuff into a 1590BB box, using off-the-shelf components... or IS it? Gentlemen, start your engines.
 
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6/24/1998 1:27 AM
Preben Hansen
This one looks to me as some sort of sytheziser controlled phasor, with all that knobs, --- (jusk a joke).  
 
But--- in the synth-wold there are a lot of interresting ways to add/substract "standard" waveform to special and complex waveforms.  
Maybe it could be a (big) project to construct some sort of "programmable" sequencer, that could be used to control phasors, and chorus/flangers as well.  
Preben.
 
6/29/1998 10:51 PM
Mark Hammer
Well, you're right in some ways; this is a BIG phaser, probably bigger than the Castle rackmount dual phaser, and the Mutron Bi-Phase, put together.  
 
As well, because the barber-pole illusion requires sophisticated voltage control, the LFO section probably IS as complex as a synthesizer.  
 
Now that I've got my scanner working, I can send you a picture of it (from an ad).  
 
As for porgammable sequencers instead of LFO's, the Blacet PhaseFilter kit ad exactly that: a "digital pattern generator". Near as I can tell, it had 14 steps/sections to generate a cyclical control voltage pattern, and s lsg circuti to generat degrees of steppiness. I suppose high resonance steppy settings get a sample-and-hold kind of sound.
 
7/1/1998 5:18 AM
paul perry

On the Blacet phase filter kit, you could probably get John Blacet himself to comment, if you post a query on the synth-diy mail list.. he is a frequent contributor, and has re-released some of his famous creations from 20 years ago or so.  
 
paul perry melbourne australia
 
7/1/1998 9:39 PM
Mark Hammer
Thanks, Paul, I may just do that. Blacet had some extremely interesting kits and design ideas at a time when I was unable to afford them. (Of course, now I can afford them but I just don't have the time to build them or even use them!)
 
7/2/1998 6:08 AM
GFR

These are the three phases of a man's life.  
 
When you are young you have the time, the disposition but don't have the money.  
When you grow up you have the disposition, the money but don't have the time.  
When you get old you have the time, the money but don't have the disposition.  
 
The above applies to sex, also.  
 
GFR
 
7/1/1998 8:39 AM
R.G.
From what little I understand of the barberpole audible illusion, the thing uses both VCA's and LFO's. The LFO is set up as a ramp, most of the sweep up, quick recovery. The VCA is a triangle, to fade the sound of one effect section up, then down. The phases are set up so that the VCA starts fading in one section of effect as the LFO ramp is going through its long up section, then fades it out as the LFO nears the end of the up section, so the volume is down while it does recovery. Then there are multiple sections with LFO/VCA's synchronized so that there is always one or more faded in at any time, and so the audible result is that you only hear an up sweep.  
 
PAIA sells a kit for a digital barberpole LFO/VCA control voltage generator last time I looked.  
 
It is NOT a 9V battery stompbox, although a 1U rack chassis should handle it nicely.
 

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