AW: AW: LDR experiments & questions

[Haible Juergen]

	>> One of the good things of LDR based phasers (besides the sound,
	>> of course)
	>
	>Can you elaborate on this please? What does sound different
compared to
	>other phasers?

Got me ! Sure there are other things than the choice of the voltage
controlled
resistor elements that are responsible for the sound of a phaser. One thing
that can make a great difference is the feedback loop: How does it limit
high amplitudes, and is there a rolloff for high frequencies - such things.

There are a few things that are special to LDRs which will make a difference
to other methods: Compared to FETs, cheap OTAs (like 3080 or 3094)
or diodes, they are quite linear at high amplitudes, which is a good thing
for the SNR. But then again, you can build very quiet phasers when you
pack these other circuits inside a compander. But in general one can
say that LDR's are very "well tempered" regarding distortion. 

Another typical thing about LDRs is their slow response, especially 
on decrease of light. So a fast rectangle or sample&hold modulation
will result in fast attack / slow decay transients. Or modulation with a
triangle
will not be much different than modulation with a sine wave at medium
rates. And often it is pleasant  to reduce the modulation depth with
increasing
modulation rate - a LDR-based phaser will do this without extra circuitry.
These are a few points that will make a LDR-based phaser different. That is
not necessarily better. Sometimes I love fast S&H modulation with sharp
transients, and then I use a transistor-ladder all pass inside a fast
compander
(the ARP Quadra phaser). For very smooth and slow timbre changes nothing
beats the LDR-based Korg PS-3100 resonator section (or the clone of the same
thing from MAM). (Admitted, this is not strictly a phaser, because it does
not
use all pass stages, but the result - several resonant peaks - can be very
similar.)
Use something different than LDRs here, and you'll loose the character
completely.

JH.