Moog Theremini Theremin

NO! - Skywave H1 is NOT a digital theremin!

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Posted: 5/22/2012 6:46:00 AM
FredM
From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................
Joined: 12/7/2007

threads posts

Thanks Jason, for adding my H1 schematics etc to TW's collection!

But I need to protest at the title! - Not because I have any pretentions about "digital" being "inferior" or the like - If I could build a digital theremin which sounded as good as the H1, I would be well pleased.

The reason for my "protest" is that the Skywave H1 was/is, in the truest sense, a hybrid of analogue and "Mixed Signal" pitch-only theremin..

The H1 had LC Oscillators driving into a MC1496 Analogue 4 quadrant multiplier, the output of which went to the audio mixer - Not a "digital" entity anywhere in the whole signal path!

Then there was a Mixed signal (wrongly, IMO, referred to as "digital" by many - "Digital" IMO means "number crunching" and not simply logic-level.. And I know, in the past I have made this astronomical mistake) "heterodyner" (not an XOR, but a D-Latch) which produced a square wave, and a divider to give a "sub octave" square wave - and these were mixed to taste in the audio mixer.

Effectively, one could accurately say that the H1 combined a fully analogue heterodyning theremin with a seperate mixed signal theremin - but even this is not precise, as both shared the same (LC) oscillators.. The two analogue LC oscillator signals are mixed (heterodyned) in a standard analogue way producing a completely analogue audio difference frequency, and, seperately, these same oscillators are squared and 'heterodyned' using logic, to provide seperate "mixed signal"audio which is mixed, to taste, with the conventional "analogue" audio.

Only the "Wrong-side of null point" indicator and muting was truly digital, and consisted of comparing the frequencies from the reference and variable oscillators, and outputting a high logic state when the variable frequency exceeded the reference frequency, and this digital aspect of the instrument does not affect the signal path at all, except to mute the audio when the thereminist moves away from the instrument.

I feel that we need to be clearer about how we catogorise theremin technologies, or we will start to create great confusion..

Truly digital theremins are only just starting to appear - Dewster is developing a truly digital theremin, and some other truly digital theremins are appearing on the market..

Most "digital" theremins (The "Glasgow" Digital theremin for example) are not "digital" at all - in the main, they are called "digital" because they use logic gates as oscillators and/or mixers - But these are "mixed signal" because they do not "crunch" numbers - they do not use the logic to perform binary computation, and their mode of operation is essentially analogue but uses signals of fixed shape and amplitude (logic level pulses) to produce the analogue output waveform.. It is a bit like saying the Mini Moog was digital because it had a keyboard which output binary states (on of off) and that only resistive keyboards which respond to pressure are analogue.

The Glasgow digital theremin is a sub-group of its own - using logic gates for oscillators and using the difference frequency to produce a voltage which drives a VCO.. It does not actually use heterodyning of any kind to produce the actual audio output.

At the end of the day, for a thereminist, the technology should be unimportant - as long as the theremin performs as they want..

And this is what bothers me - Standard logic gate RC oscillators are inferior to LC oscillators, and "digital theremin" has sadly now been equated to nasty cheap theremins which are unplayable and sound horrible, because they are equated to anything using RC logic gate oscillators! - most of these type of oscillator are unsuitable for use in theremins due to their nonlinearity.

"real" Digital theremins designed for high performance will probably use good LC oscillators at the front end, in order to obtain maximum stability and SNR on which to perform the computations required.

Digital theremins, like Dewsters project, have the potential to be good musical instruments meeting all the requirements thereminists want, as do mixed signal theremins (as proven by the E-Pro).

But, at this time, Digital theremins have not yet "come of age" - and the theremins which are being labelled "digital theremins" are usually awful, and the reason for this is not, or may not be because they are "digital", it is because most of them are just cheap sh*t using cheap logic gate RC oscillators.

Fred.

 

Posted: 5/22/2012 1:31:19 PM
Jason
From: Sammamish, Washington
Joined: 2/13/2005

threads posts

Whoops!  Thanks for pointing this out.  I will correct the title. 

Posted: 5/22/2012 2:38:20 PM
RS Theremin
From: 60 mi. N of San Diego CA
Joined: 2/15/2005

threads posts

Fred I understand all your frustration after yesterday. The Doc says he needs to do a Digital examine and when he was done you argued it was Anal og.

For me analog is found in nature the same as AM radio waves. Where digital is unnatural man made square waves (logic levels) or as unnatural as FM radio waves. My use of pulse width modulation I would call unnatural and slightly digital.

So if Digital is unnatural or one finger then I guess the Doc was correct?

What is disturbing about having so many tests, barium, scopes, cat scan, etc and your in "extreme discomfort" and now worse shape from all the tests is when the Doc comes back and says you can go home as there is nothing wrong with you!#$%^&

Yes, I have been there also in the past year.

Did you hint about a theremin curse?

Christopher

Edit: Fred it may be my diabetic imagination but I eliminated all artificial sweeteners from my diet and sugar substitutes like corn syrup. The irritation seems less severe on the "complete" dietary tract. Not healed but better. (-:

Posted: 5/22/2012 2:49:21 PM
dewster
From: Northern NJ, USA
Joined: 2/17/2012

threads posts

"Logic gate oscillators are inferior to LC oscillators..."

Picking a highly tangential nit and almost certainly putting words in your mouth, but CMOS logic gates (inverters) are used literally everywhere for sense & drive in very stable crystal oscillators.  I was using this same configuration as an LC oscillator in my AFE (before I switched to DPLL sense & drive) and was very reluctant to leave that circuit because it worked so well.

Posted: 5/22/2012 11:30:08 PM
FredM
From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................
Joined: 12/7/2007

threads posts

Thanks Jason - Yeah, I know I am a pedantic grumpy old man! LOL.

dewster - You are right, I have edited my posting to make things a little clearer (I hope) and a little less emphatic!

Ok - the following is medical rubbish probably only of interest to fellow sufferers and those who are not squeemish - Nothing about theremins!

Christopher - "Fred it may be my diabetic imagination but I eliminated all artificial sweeteners from my diet and sugar substitutes like corn syrup..."

I dont take artificial sweeteners unless by accident, and yes, some people can have really bad 'subtle' reactions - particularly to aspartame (IMO, aspartame should never have been licensed).

"What is disturbing about having so many tests, barium, scopes, cat scan, etc and your in "extreme discomfort" and now worse shape from all the tests is when the Doc comes back and says you can go home as there is nothing wrong with you!#$%^&"

Yes, I know that one! - But this time I am extremely happy to have been sent home without them finding what they were expecting to find!!

Fred.

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