EHX octave/harmonic generators?

Dozius · 18 Jan 2012

I would imagine it uses a frequency dividing circuit. Typically done with flip-flops.

a good start would be something like:

in -> wave shaping -> frequency divider -> octave down signal

trogluddite · 19 Jan 2012

Dozius wrote: Typically done with flip-flops

Spot on...

EHX tone tips wrote: The Octave Multiplexer uses an analog flip-flop circuit to produces a unique, fat, grainy sub octave tone

Careful how you model that "analogue" flip-flop though - the high/low bi-stable output is probably created using a special arrangement of "analogue" transistors - quite unrelated to those horribly un-musical digital transistors used in your CPU. It's well known that binary on/off signals generated with analogue circuits (preferably with valves/tubes) sound much more "fat and grainy"! 😉

There's a good description of the principle on this site...LINK

Leslie147 · 12 Mar 2012

The 'Eureka moment' for me came when I realised that in many of the 'octave dividers' they multiply the input audio signal by the (bipolar) square wave(s). Then there's no question of having to make the amplitude of the square wave(s) track the amplitude of the input signal. The resulting DSB modulation of the input signal can sound like 'ring modulation' with some input signals, for obvious reasons.

Chris

oddson · 12 Mar 2012

There are lots of octave dividers that rectify the input, DC shift, and then filter the nastiness of the sharp change at what was the zero-crossing.

But how it adds other harmonic series elements and lower octaves I don't get.

And there's also how it manages to claim to be polyphonic. I can see how some of this might work with a single note but not really how they can track chords from a single input. 😕

Leslie147 · 12 Mar 2012

I wouldn't have thought adding harmonic series particularly difficult. Many years ago I made a hardware gadget using a 4046 PLL and a divider chain, phase locking to to a filtered, compressed, squared input guitar signal. Having a clock at 256 times (or whatever it was) the dominant input frequency provided lots of scope for creating harmonic series.

The extent to which the recent EH devices are truly polyphonic seems a bit vague from the material on YeweToob, although there certainly seems to be a few notes' worth. With devices out now like the TC Electronic PolyTune (http://www.tcelectronic.com/polytune.asp), that can analyse six notes at a time from the input signal, it would seem that scanning correlators and suchlike are becoming commonplace. If you know the frequencies of the (up to) six notes from a guitar signal, creating harmonics of each should be straightforward. I recall there are other threads on this forum concerning pitch detection.

Chris

oddson · 12 Mar 2012

That's really my question... does EHX use dsp and pitch detection algorithms or are these analog devices that uses analog signal processing tricks to generate harmonic signals.

(I'm nearly certain the TC Polytune would be digital but EHX seems to eschew dsp in their boxes.)

EDIT - answered. I saw a gut-pict from their forum showing what looks to be a DSP chip in the POG. I guess I could have aske the question there! 😊

Leslie147 · 12 Mar 2012

Indeed, and the downloadable instruction manuals for devices such as the HOG contain text such as 'Ideally, you want to set the INPUT GAIN slider so that you have maximum signal level at the A/D Converter but does not clip the A/D.'

Digital all the way it would seem nowadays, at least for these complicated effects. I've read that the TC tuner is DSP-based as well and, although they may not state as much on their web site, the offer to 'Download PolyTune Drop-D Software' is a bit of a give-away.

I wonder when all the patents pending will be filed, so we can take a look. Mind you, if they're anything like what Line-6 got away with, concerning the Pod, they won't tell the full story.

Chris

infuzion · 12 Mar 2012

Leslie147 wrote: I wonder when all the patents pending will be filed, so we can take a look. Mind you, if they're anything like what Line-6 got away with, concerning the Pod, they won't tell the full story.

Doesn't mater in the USA anymore; patent law has been changed to "first to file". So if I can figure out how EHx did it, & I file before they do, then I get the patent! They can legally keep using it for free, but I get to charge everyone else who tries to make their own. MUHAHAHA 😈

This is why Apple, Google, IBM, MicroSoft, Samsung, & their cat are having law-suit orgies now.

cyto · 13 Mar 2012

Just to clarify...

Yes, the new ones (POG, HOG, etc) are digital. The older ones on that page (all the micro-synths, the frequency analyser (RM), the octave multiplexer, etc.) are completely analog. Granted, they don't have the sophistication (ie poly-tracking) of the newer ones, they are cool devices nonetheless.

-cyto