Synth-DIY Yahoo! Groups Archives

Thread

S&H random modulation generation.

2010-01-05 by Russ

"A high frequency sine wave sampled at low frequency will resemble a random number generator.

An infinitely high frequency sine wave sampled at infinitely low frequency would be a true random number generator. Except that since the sample rate is infinitely low, it would take an infinite amount of time to prove it.

;-)

Mike"

Isn't this why a lot of random number generators are called quasi random?
I know on my Moog MG1 if I pull up the random modulation and lopass it just right at certain speeds it is definitely a repeating pattern. I have read elsewhere that the random mod is a S&H circuit. (my aoplogies for bringing up a synth other than the Poly 800, both my polys get used a lot even with a moog and a DX in the studio).
I still plan on getting one of the hawk mods off of you Mike, I have just had a roller coaster of a year. 2010 looks to be better already though. I already fixed a DX27, a realtube preamp andI discovered a stash of vacuum tubes I forgot I had. Found some nice RCA 12ax7's that I cannot believe were just sitting there!

Re: [korgpolyex] S&H random modulation generation.

2010-01-05 by Atom Smasher

On Tue, 5 Jan 2010, Russ wrote:

> Isn't this why a lot of random number generators are called quasi
> random? I know on my Moog MG1 if I pull up the random modulation and
> lopass it just right at certain speeds it is definitely a repeating
> pattern. I have read elsewhere that the random mod is a S&H circuit.

=================

i'm not familiar with that synth in particular, but having a fast wave
sampled by a slow wave is a "random" LFO design that i recall from 555
timer cookbooks, and similar circuit design tutorials.

these things are sometimes called "quasi random" (or similar) because
that's what they are. true random, in any engineering sense, is hard to
implement. and bob moog was more of an engineer than anything else.

> (my aoplogies for bringing up a synth other than the Poly 800, both my
> polys get used a lot even with a moog and a DX in the studio). I still
> plan on getting one of the hawk mods off of you Mike, I have just had a
> roller coaster of a year.

==============

i don't think anyone here expects you to use only one synth ;)

mike and i have certainly mentioned other synths. it's where we steal
ideas^H^H^H^H^H^H^H^H^H^H get inspiration from. you won't loose points
just for that.

> 2010 looks to be better already though. I already fixed a DX27, a
> realtube preamp andI discovered a stash of vacuum tubes I forgot I had.
> Found some nice RCA 12ax7's that I cannot believe were just sitting
> there!

================

i'm with ya on 2010 looking better... already... ;)

--
...atom

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Re: S&H random modulation generation.

2010-01-05 by gordonjcp

--- In korgpolyex@yahoogroups.com, Russ <russdaren@...> wrote:

> Isn't this why a lot of random number generators are called quasi random?
> I know on my Moog MG1 if I pull up the random modulation and lopass it just right at certain speeds it is definitely a repeating pattern. I have read elsewhere that the random mod is a S&H circuit. (my aoplogies for bringing up a synth other than the Poly 800, both my polys get used a lot even with a moog and a DX in the studio).

"Pseudo-random". The Moog MG-1 used a single-chip pseudo-random noise generator, the MM5837. Since its output *does* repeat, then sampling at a low rate would give you a fairly long cyclic pattern. There are a couple of sites out there with replacements for this chip based on cheap off-the-shelf microcontrollers.

Gordon MM0YEQ