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Through Zero Oscillators
MUFF WIGGLER Forum Index -> Modular Synth General Discussion Goto page 1, 2, 3, 4, 5, 6  Next [all]
Author Through Zero Oscillators
southphillysynths
Through zero oscillators are something that I totally forgot about until just now. hihi

I have a few questions about it, Not how to patch it/what to use it for, more about the history and stuff.

What does it look like on a scope?

Where did this idea come from? In the new modular stuff, yes there are a lot of new ideas, but a lot of the time it is trying to bring back old stuff. (which is awesome and totally cool if theres new ideas I'm not arguing that) But to me, it does not seem that there was this old monosynth that had through zero and they put it in a module and everyone copied it. So what is the history behind the first designes and where did this idea come from? Was there one osc/ format that started it all?

Can we get a list going of oscs that have it? I know the Intellijel Rubicon does, and there was a blue lantern osc that I vaguely remember with TZ (does ayone have one?) But I don't know beyond that...
stk
Hertz Donut does it too.
I don't know much about the technical side of TZ, only that the Donut's FM spoiled me for FM, none of the other oscillators I've tried can get that lovely glassy tone (although from what I've heard the Rubicon can, so I guess it's probably a TZ thing).
Luka
Search and ye shall find
Dr. Sketch-n-Etch
There are currently three analog options for through-zero FM:

Intellijel Rubicon (euro)
Cynthia Zeroscillator (various formats)
Fritz Teezer (5U, others?)

There are also various digital options:

Intellijel Cyclebox
Harvestman Hertz Donut
others?

It's a fairly old idea, but not one which is very easy to implement, and therefore has not seen much use. However, given the amazing sounds of which TZFM is capable, the situation is changing now.
Dcramer
So on the original HD will it do TZFM when being modulated by its second oscillator ?
frijitz
southphillysynths wrote:
What does it look like on a scope?

Three videos with scope traces:
http://www.youtube.com/user/frijitz001

Quote:
Where did this idea come from?

Radio communications.

Quote:
So what is the history behind the first designes and where did this idea come from?

There were early synth circuits in Electronotes from Bernie and from Jan Hall. Other diy versions came from Don Tillman and Henry Wamsley. These all used different methods!

Ian
Agent86
frijitz wrote:
There were early synth circuits in Electronotes from Bernie and from Jan Hall. Other diy versions came from Don Tillman and Henry Wamsley. These all used different methods!

Thanks for the lead on Henry Wamsley, I found an article in EDN from 2003. (I assume this is the one? http://www.edn.com/design/test-and-measurement/4330221/VCO-produces-po sitive-and-negative-output-frequencies)

I had read Don's article some years ago (seems he still hasn't finished writing it) and I just skimmed Henry's. Some day I hope I'll actually understand what I read!
hmmm.....

I'm dredging through my old brain for a connection... Years ago, I remember reading a comparison of frequency shifters that used either digital or analog oscillators and I was wondering if this is related...
Dr. Sketch-n-Etch
frijitz wrote:
These all used different methods!

Yes, and the Rubicon uses yet another different method to all of these.

BTW, I wish we didn't call it "through-zero FM". It is much better understood as "balanced FM" because it is then analogous to "balanced AM".
sonicwarrior
Dr. Sketch-n-Etch wrote:
"balanced AM".


Is that the same as ring modulation? If yes, I am not sure if even that is widely known.
frijitz
sonicwarrior wrote:
Dr. Sketch-n-Etch wrote:
"balanced AM".

Is that the same as ring modulation? If yes, I am not sure if even that is widely known.

Never heard the term "balanced AM" used. "Balanced modulation" usually refers to AM, AFAIK. TZ FM is used in an unbalanced condition most of the time. Plus the term "through zero" carries the implication that special circuitry is used to allow negative frequencies and the attendant richer spectrum.

Ian
neil.johnson
Balanced amplitude modulation used to be done with a device known as a ring modulator. It is useful in comms design as you don't get (in an ideal balanced system) any carrier signal, just the side bands. Take the double side band (DSB) output of the balanced modulator, then filter out one side band, and you get the familiar single side band (SSB), or include a little bit of the removed side band for vestigial side band (VSB) used in analogue TV systems.

Neil
Dr. Sketch-n-Etch
This is just how I think about these things.

The Intellijel uMod has a "Q Balance" knob which gives balanced (four-quadrant) AM in the centre, and unbalanced (two-quadrant) AM at the extremes.

The Symmetry knob on the Rubicon does exactly the same thing in the FM realm.
wellurban
Dr. Sketch-n-Etch wrote:
There are also various digital options:

Intellijel Cyclebox
Harvestman Hertz Donut
others?


Braids has three digital FM models. Am I right in presuming they'd be TZ?
BTByrd
Dcramer wrote:
So on the original HD will it do TZFM when being modulated by its second oscillator ?


Yep! And the external FM input can be switched between exponential FM and linear thru-zero FM.
101010oxo
BTByrd wrote:
Dcramer wrote:
So on the original HD will it do TZFM when being modulated by its second oscillator ?


Yep! And the external FM input can be switched between exponential FM and linear thru-zero FM.


Damn, I should _really_ read the documentation! thumbs up
101010oxo
101010oxo wrote:
BTByrd wrote:

Yep! And the external FM input can be switched between exponential FM and linear thru-zero FM.


Damn, I should _really_ read the documentation! thumbs up


And so I did: Holy sh*t! This has some serious complexity under the hood. I'll be happily busy for quite some time smile
buddard
And according to the recently released manual (www.theharvestman.org/pistonmk2.pdf), the Piston Honda mk2 also seems to support external TZFM:

Quote:

CV is a unipolar, exponential frequency input, and FM is an AC-coupled audio
input for thru-zero frequency modulation.



Cool, huh?
drumsofd00m
Just a quick note off the top of my head (I posted this before in another thread and no one corrected me, so I hop I'm still getting this right after many years):


AM (amplitude modulation) = four quadrant multiplication (output = both original signals + sum of all frequencies/ partials in either signal + difference of...)

Balanced modulation/ Ring modulation = two quadrants (only sum + difference, original signals oppressed)

Frequency shifting/ single sideband modulation (SSB) = "single quadrant" I guess, although I haven't read that term I think. Separate outputs for upper & lower sideband (sum and difference).

Through zero frequency shifting/ "barber pole phasing" = when the reference input in SSB, well, crosses through zero. No, I don't know what that means, technically ^^
All the classic frequency shifters (EMS, Bode, Buchla) had different problems doing that (either stepping because the reference "LFO" was digital or the output just stopped below a few Hz). - I have no idea how modern units do. The Buchla 297 seems to implement only the infrasonic part/ the barber pole phasing quite well, and there are now through zero FM VCOs, so maybe things changed.

Hope that helped a little bit in understanding the concept of "through zero modulation", even though it's not about FM directly.

There's also some confusion about PM (phase modulation) and (Yamaha-style/ linear/ potentially through zero) FM. Contrary to what some people think and write all the time, they are not the same. Someone else would have to epxlain that though.
blooma116
Through-zero oscillators simply flip phase when the frequency is negative... which is what makes them through-zero; whereas a normal oscillator simply outputs silence when the frequency is 0 or less. Also, I know that FM creates sidebands (harmonics above and below the carrier frequency governed by a bessel function) based on the frequency relationship between the carrier and the modulator and the index, i.e. depth of modulation. When the index is high enough, the sidebands below the carrier will eventually reach zero, and the difference between a non-through-zero oscillator and a through-zero oscillator is that the through zero oscillator will generate the phase flipped frequencies which will dynamically cancel the other sidebands based again on the bessel function math and the index (true FM). I assume that ideally, with a low enough index (where the sidebands don't cross zero) a through-zero oscillator and a non-through-zero oscillator would sound the same, though I don't have any practical experience here. How useful are high index sounds created with non-through-zero oscillators compared to through-zero oscillators? Can anyone with else comment on this?

DX7-style FM is actually phase modulation synthesis, which from what I understand gives technically the same results as FM, but is practically implemented in a different way... a topic which is currently beyond my understanding. I also know that a big reason why FM didn't really make it big until digital became more common is because of tuning stability, and the difficulty of getting clean FM sounds from analog (which is a big reason for the tonal differences, and why I'm sure many people prefer one to the other). I always thought the digital FM was a bit sterile-sounding and love the vibrancy of analog FM, especially now that an analog oscillator can be pretty accurately tuned, but I'm sure there's cool digital implementation of FM out there nowadays as well. Some people say it sounds really cool on the Hertz Donut, just not a big fan of DX7-type sounds. What I'm curious about is whether whether any of the complex oscillators available out there are through-zero or not? Skimmed through a few manuals but didn't immediately come across this distinction in anything except single oscillators which specifically claimed to be through-zero.
slow_riot
Mine is...

https://aether-machine.com/oscilloplasm/

It's not in eurorack format though. The tuning stability is a good as you can do in analogue. Couple months away from taking sales.

Most of the complex analogue oscillators in euro are based on the Buchla 258 or 259 and are not TZ.

To be honest, I prefer gentle FM, and the way i use the oscillator the TZ part is not life changing. At lower frequencies where the rate is close to 0, the extra dynamic range that TZ brings to FM helps keeps things tonal. And occasionally it is nice to drive the FM into more abrasive territory.

For me, the more important features in a complex oscillator are very clean modulation oscillator, and ability to generate complex harmonics in the carrier osc.
Abyssinianloop
Sounds a lot like middle out compression oops seriously, i just don't get it oops
ndkent
The Cyndustries Zeroscillator was I believe the first commercially sold unit though I understand the concept in a synth context first appeared in Electronotes.

It's worth noting that nothing vintage does it

How I explain it to people (fairly) simply is every voltage controlled oscillator is capable of some sort of frequency modulation. You are changing the pitch of the oscillator receiving the modulation (carrier) at an audio rate with another oscillator (the modulator) that you aren't directly outputting as audio (though nothing stops you from experimenting). The goal is you get an output tone color which is different from the basic waves an oscillator has. With some special oscillator FM behaviors though you get different results that may be useful.

It's fairly obvious that the frequency you are modulating with (modulator) will have an effect on the tone color of the output. What is maybe less obvious is the depth (amplitude) of the modulator plays a big role in the tone color, which at least to me at first glance is a fairly abstract but critical idea.

Simply modulating frequency is called Exponential FM. You can make some wild sounds but what you don't get is something consistently playable for pitched music as you change frequency. You don't get the same change in frequency on the positive and negative portions of the modulating wave

Linear FM as a modulation input option addresses the timbre change as frequency changes. It's an option found on some vintage gear though not the majority of VCOs. It lets you effectively do FM modulation and the timbre can change pitch and stay the same basic timbre.

Once you are doing linear FM, another limitation of modulation amplitude changing the tone color kicks in. Enough negative modulation amplitude will tell the carrier to slow down to a zero frequency and not stop there. In practical terms it just sits there for part of a wave cycle until the modulator sends enough voltage to be oscillating at a frequency. The tone color changes in usually not a desirably way as you hit zero frequency for some of the wavecycle.

So that situation is addressed with a through zero capability of letting you modulate a carrier VCO past a zero frequency into a "negative" frequency represented by phase inversion. The result is the carrier does something in terms of frequency instead of sitting there part of a cycle and a much larger amplitude FM modulation is possible.

It's ironic to me that some artists who do sort of abstract often unpitched and potentially chaotic music have heard somewhere that they have to get thru-zero FM oscillators because they heard that somewhere. Now not to discount the extra capabilities are just that and linear FM and through zero doesn't stop you from doing crazy expo FM madness. But my ironic point is it might not be critical for their results.

Finally my hint is FM is kind of boring and unimpressive - through zero or not - if it just gets dialed in and sits there. What makes it exciting is changing the modulator amplitude over time typically with a VCA. Then what gets my goat is people just patch one VCO to another cranked at full amplitude and say "X" does great FM if they liked the sound which is partly due to the carrier. Or "I didn't care for the FM" when they simply crank up the knob on play with the carrier frequency
wsy
TZFM is handy to have (IMenlightened-but-still-humbleO) because when you go negative on a regular osc,
the action just stops and your ear hears it as a glitch.

Which is fine if you like glitchy audio. And glitch audio has it's place (sez the guy using a Synchrodyne as an oscillator), but
more tonal music deserves different treatment.

As to what TZFM looks like on a scope, here's the videos I did on the FM Operator, which have some scope
time (and also spectrum analyzer time).

The spectrum analyzer shows the effect of TZFM when you hit zero - TZFM goes negative, which on a spectrum
analyzer (and your ear) folds back UP into positive frequencies. So that's where that rich semiharmonic structure
comes from - the folding in frequency space.

Here's the vids:

http://www.youtube.com/watch?v=XSRti_YKYlo

http://www.youtube.com/watch?v=uMSq8KraeCA

http://www.youtube.com/watch?v=lKmg0SzjhwA

- Bill
loki
John Chowning published a tutorial article on FM synthesis in the September 1973 issue of the Audio Engineering Society Journal. Google will lead you to several sites where you can download it.

He was doing his synthesis on a PDP 10 at the Stanford Artificial Intelligence Lab. Everyone doing analog synthesis thought it would be really cool to be able to do this without having to drop a couple of million on a computer. Bernie Hutchins wrote about it in Electronotes.

Chowning patented the technique and Yamaha licensed the patent and the end result, in the '80s, was about 300,000 Yamaha DX7s.

(edited to insert Intelligence into: Stanford Artificial Intelligence Lab)
Dr. Sketch-n-Etch
drumsofd00m wrote:
Just a quick note off the top of my head (I posted this before in another thread and no one corrected me, so I hop I'm still getting this right after many years):


AM (amplitude modulation) = four quadrant multiplication (output = both original signals + sum of all frequencies/ partials in either signal + difference of...)

Balanced modulation/ Ring modulation = two quadrants (only sum + difference, original signals oppressed)

Frequency shifting/ single sideband modulation (SSB) = "single quadrant" I guess, although I haven't read that term I think. Separate outputs for upper & lower sideband (sum and difference).

Through zero frequency shifting/ "barber pole phasing" = when the reference input in SSB, well, crosses through zero. No, I don't know what that means, technically ^^
All the classic frequency shifters (EMS, Bode, Buchla) had different problems doing that (either stepping because the reference "LFO" was digital or the output just stopped below a few Hz). - I have no idea how modern units do. The Buchla 297 seems to implement only the infrasonic part/ the barber pole phasing quite well, and there are now through zero FM VCOs, so maybe things changed.

Hope that helped a little bit in understanding the concept of "through zero modulation", even though it's not about FM directly.

There's also some confusion about PM (phase modulation) and (Yamaha-style/ linear/ potentially through zero) FM. Contrary to what some people think and write all the time, they are not the same. Someone else would have to epxlain that though.

Nearly everything said in the quoted post is wrong.
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