single stage phase shift? who thinks this is worth building?

[Mark Hammer]

I think it would be important to distinguish between amount of phase shift (i.e., # degrees) and where the shift is applied across the spectrum.  The bandwidth of the signal being shifted might also make a difference too, I suspect.

If I've understood phase-shifting properly (and I hope Mike Irwin can confirm that I did), the phase shift applied varies in degree according to pitch, not unlike any other type of filter (phase-shift stages are allpass filters).  If I had a single-pole lowpass filter, I would expect  little impact of sweeping that filter up and down if the bandwidth of the input signal was narrow, or rather, too narrow for the amount of sweep and filtering applied.  I imagine the same thing applies here.  Without even looking at the circuit, I would guess that feeding it a bass and rolling off the tone control on the bass would yield diddley-squat in terms of any noticeable impact of the single allpass stage, except maybe at higher modulation rates (e.g., in the audio range; remember that faster modulation is generally perceived to be more "intense" because of the rate of change).
 Feed that same device a well-mic'd sample of a string section, modulate it at something a little faster than maybe 2hz, and I suspect you would be able to "hear something".

Is that a plausible compromise?[/i]

[R.G.]

You're on it, Mark.

1) phase shift is approximately the same as time shift for the small range of frequencies for which the phase changes.
2) single phase stages have a usable phase shift area of about 90 degrees +/- 45 degrees, and a frequency range of the shifted area of about one decade centered on the 90 degree phase point.

A single phase shift stage with no dry signal mixed back in will cause a vibrato effect in a single band of frequencies that moves around as the modulation moves. If the signal doesn't happen to have any partials in the effective frequency range, you hear nothing (except perhaps vibrato-ed hiss). If the signal is in the shifted range, you hear a slight vibrato effect. This is more noticeable the faster it moves (LFO speed) and the higher the frequency (human ear sensitivity).

From some experiments I've run, I have proven to myself that the reason the univibe phase stages have cap values strung out in that odd way is that the treble ones are 10:1 apart because of the effective range of the phase stage and get closer together at the bass because of the lesser effect at bass frequencies. They're different to spread out the vibrato over the audio range, not concentrate it at one point. This compromises the phasing sound a bit, but improves the vibrato a lot.

Nota bene: flipping a phase invert switch is not even close to what you'd hear from a single phase stage. The instant phase invert he heard as a transient, not any kind of modulation, unless the flipping is repetitive, in which case it starts sounding ring-modulator-ish, not phase-ish or vibrato-ish.

A single phase stage can give a slight vibrato in one frequency range if well done. If the spotting of the sweep range matches the frequencies of your signal, it's a useful effect, as Magnatone proved.

[Tim Escobedo]

FWIW, I just breadboarded a single stage, single transistor phase shift circuit modulated by a simple Phozer-like phase shift oscillator. Wet signal only yielded a OK vibrato. Actually, I was pleasantly surprised at the quality. One or more added in series with the staggered center frequencies I suspect would be quite nice.

[R.G.]

FWIW, I just breadboarded a single stage, single transistor phase shift circuit modulated by a simple Phozer-like phase shift oscillator. Wet signal only yielded a OK vibrato. Actually, I was pleasantly surprised at the quality. One or more added in series with the staggered center frequencies I suspect would be quite nice.

Yep. Once you find the path, you reach the univibe pretty quickly.

Magnatone would have done it years before if it didn't cost two 12AX7's per stage in that technology. The organ people did this long ago. See "Electronic Musical Instruments" (which meant organs back then.)

[puretube]

tnx, R.G. for xplaining w/ more words...
the "univibe" thingy is based - like noted sev. times -
on the findings of mr. Dome (!) (late 40`s),
who elaborated mr. Bode sr.`s (!) works.
(see EPO: "wide band phase shifter" a.o.).

R.G.: quite a while ago, I gave you a little riddle (    )
about a different way to produce the vib FX:
the solution is:
"AM" 2 quadrat.-signals, and mix them.
(that`s what the late great Dick Denney (VOX) lent from the
-copying each other- organ-guys that were inspired by Dome...)

-kudos for these guys that keep on inspiring me-

[zachary vex]

...Nota bene: flipping a phase invert switch is not even close to what you'd hear from a single phase stage. The instant phase invert he heard as a transient, not any kind of modulation, unless the flipping is repetitive, in which case it starts sounding ring-modulator-ish, not phase-ish or vibrato-ish....

ahh, all your years working as a recording engineer taught you this, i imagine.  8^)  

tell me, RG, have you ever, even once, listened closely to the sound of a phase switch?  i have, hundreds of times.  at the moment of phase switch, a pitch shift is heard.

[puretube]

Seen the current immense interforumal interest in Mr. Richard H. Dorf`s contributions concerning Wurl*tzer vibratos,
it`s about time to disclose his vibrato-invention here:
"Electrical Musical Instruments"

[puretube]

Seen the current immense interforumal interest in Mr. Richard H. Dorf`s contributions concerning Wurl*tzer vibratos,
it`s about time to disclose his vibrato-invention here:
"Electrical Musical Instruments"

Which is probaly not the one that`s built in this here Wurlitzer 44..., or?

[R.G.]

ahh, all your years working as a recording engineer taught you this, i imagine.  8^)  

tell me, RG, have you ever, even once, listened closely to the sound of a phase switch?  i have, hundreds of times.  at the moment of phase switch, a pitch shift is heard.

So zach, are you just looking to pick a fight? Slow day back at the office?

[Boogdish]

RG, you realize that post is from five years ago, right?

[frequencycentral]

Yeah. major necro-bump there! But this is the article being referred to: http://www.thermionic.info/dorf/Dorf_TheWurlitzerVibrato.pdf

[panterafanatic]

RG, you realize that post is from five years ago, right?

RG had the second post of today actually. he probably didn't read the post before when the thread previously died.

[R.G.]

Yep, you are correct. I'd like to say I was in a time warp, but what happened was that I saw the thread come up, read back a couple of posts and reacted.

I'll modify it if I still can. My bad.