From sdiedrichsen@b-three.de Wed Apr 06 07:47:07 2005
Subject:Re: Chorus/ vibratoeffect Way to go. - a divergent view


Am 06.04.2005 um 15:47 schrieb Kevin:

> I'm an electrical/electronic/computer engineer of 28 years and for
> the first 10 years of that career I was involved in the design of
> magnetic measurement equipment which made extensive use of inductors
> and capacitors in the production of magnetic fields, tuned circuits,
> and low and high pass filters.

That sounds good. I'm senior software application engineer with an EE
degree.

>
> Build one - a single node with a series inductor, and on the other
> side of the inductor a shunt capacitor to ground, inject a sine wave
> into the inductor, and measure the input and output voltage waveforms
> with a 2-trace oscilloscope.  Take a function generator and vary the
> frequency of the sine wave and you will see the phas shift vary with
> frequency.  That is unless somehow the laws of physics have been
> redefined :)

This is the same with a time delay. Take your soundcard in's and Out#s
, launch a recording software, that allows monitoring, and repeat the
experminet above.
The phase will vary and rotate vs. frequency. In contrary to an LP,
where phase shift ends at 10*cutoff frequency (not exactly), phase
shift goes on.
>

> A simple analysis takes one node of the delay line.  This is an LC
> low pass filter.  The entire delay line is a series of these with a
> given frequency having a small delay at the beginning of the line and
> the same frequency having a larger delay at the end of the line.  But
> the phase and thus delay as a function of frequency will be different
> for another frequency. The effect is cumulative as you travel down
> the line.

This is the error in the thought experiment: We have a passively
coupled system here, cumulation might occur, but not as desired. Phase
response is flattened as the amplitude response.

>
> As you progress along the taps in the line at any given instant there
> is an increased time delay for the same signal.  If you had a true
> TIME delay the delay would be constant regardless of frequency.

And this is the case. Believe me. The delay is (of course not
perfectly) constant. In the case og the hammond delay line, we have 18
inductors and caps,

>
> Summing the delayed signal with the dry signal results in the
> modulation which we know as "Hammond chorus"

Right.

>
> Have you ever BUILT one of these and heard it??
>
I implemented those things in software. The phase shifter design
doesn't sound like Hammond vibrato. The time delay thing does, with a
few tweaks.
If you want to have a look at my SPICE simulations results, email me
privately.

Best,

Steffan

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