FS and "AKO Phasing" update

[Haible Juergen]

Ok, first two corrections, after I tried several things last night.

First, the continuous risising phaser effect is really there, with
the FS alone. I noticed it as I listened closely: One "sweep" starts
at lof frequencies, rises, and fades out at high frequencies. Then
another one starts at the low end. Sounds like sawtooth modulation,
only without a reset glitch. The effect is a quite subtle one, however.
Maybe I had expected something like the continuously rising sound
at the end of Floyd's "Echos" - this is not.

Second, another look into Bode's patent showed that he uses
a configuration with a pure all pass filter in front of the FS, and
not a whole phaser/comb filter as I thought. Sorry Don - you
were absolutely right. The effect is there (slightly). And you can
further increase the effect with additional phase shift in front of the
hilbert transform network. I tried pure all pass, a complete phaser,
and a phaser with its own resonance. All different, and all interesting.
(This was just one feedback path from the FS output to its input.
Haven't tried bode's more complicated structures yet.)

Now, to clarify one possible misunderstanding which came up
on AH: Of course my FS has a dome filter / hilbert transformer
as well. It's just not included into the set of my schematics on the
web, because it's identical to the Electronotes Frequency Shifter's
one. Reason not to publish it? I want to avoid legal trouble,
I want you to buy the original EN, and (more serious), I was too
lazy to redraw it. But it has to be connected between the
compressor output of the Noise Reduction, and the 2 Signal
inputs of the Modulators. You need capacitive coupling for the
later connections (1uF) to avoid a bad DC offset. (This is *not*
GND referenced!) If you want a pure sine/cosine VCO without
the modulation, you can simply short these inputs to GND, providing
the necessary DC offset without an external voltage.

	>This is similar to the Lesley dual doppler effect where you
would have
	>an table close to this:
	>
	>Number	Original	Horn1	Horn2
	>1	100		99.8	100.2
	>2	200		199.8	200.2
	>3	300		299.8	300.2
	>
	>And so on... 
	>
	>Horn1 - moving away from you
	>Horn2 - moving towards you
	>
	>This is shifting...

About Lesley: I always thought the doppler effect would really cause
a pitch shift, not frequency shift, but I am not sure at all, so I have
to
think of this again.
Most important is if you try to approximate it with delay lines, you
have
to modulate the clock *period* with a sine wave, not the clock
frequency. The famous Dynacord CLS-222 does this.
On the original Lesley there is only *one* Horn (the other one is
a fake, and only needed for mechanical balancing!), but with all
the reflections inside the cabinet it probably ends up with two
(or more) shifts in opposite directions nevertheless. (The CLS-222
uses 2 BBD lines for the rotor, too.)
BTW, there's an excellent article about the Lesley at

http://theatreorgans.com/hammond/faq/mystery/mystery.html

	>The Hammond Scanner Vibrato where Hammonds attempt to get the
Lesley
	>effect without the Lesley cabinets, this was not such a great
thing so
	>Hammond ended up bying the Lesley company to get the right
effect
	>along with their organs... (if I recall things rigth, I am sure
	>someone will correct me if I am not right).

Yes, Hammond actually did *fight* against these Lesleys,
so I was told. But the Scanner Vibrato is a classic as well,
and a gem of its own. Well worth building a clone without
oil and migrating metal particles inside.

>  JH.