VC Phaser using the LM13600

[Don Tillman]

   From: jorgen.bergfors at idg.se
   Date: Thu, 7 Jan 1999 9:35:26 +0100

   Well, I suppose my question should have been: Which of the
   commercial phasers use lagging and which use leading filters? Can
   the Hammond scanning vibrato be considered leading or lagging? 

The Hammond scanner lags, but it's a delay line, not a phase shifter.  

   From: Haible Juergen <Juergen.Haible at nbgm.siemens.de>
   Date: Thu, 7 Jan 1999 12:24:58 +0100 

   I have a stupid question: Does this leading / lagging distinction
   make any sense at all ? 

No difference at all.  It's just signal inversion (and individual
circuit peculiarities, of course).

   Date: 07 Jan 1999 14:46:00 +0200
   From: fa_diy at fa.camelot.de (Florian Anwander)

   To my knowledge you are theoretically right, but practically a
   "phaser" is not a perfect delay. It is an allpass filter, which
   makes a delay, but only below the centerfrequency. 

Phase shift and delay are very different and should not be confused.

A phase shifter circuit really has no delay, above or below the center
frequency.  It just shifts the phase.  This is important: any change
at the input of a phase shifter will always show up in the output
immediately.

The amount of phase shift in a phase shift circuit below the center
frequency is roughly equivalent to the measured phase shift of a delay
line, but that's a case of two different processes measuring
similiarly on some arbitrary gauge.

  -- Don