Synth Expert Please Help!

[Equilibrium]

Hmm I am really scratching my head here. I managed to get my hands on FM Theory & Application by John Chowning, but I have hit another point of misunderstanding.

The task is to make a squarewave out of sine waves. Obviously as it was designed for the DX series you can only achieve the first six harmonics. I understand that the amplitude of each harmonic is a fraction. The number of the harmonic goes on the bottom, and a 1 goes on top. (Maths degree, no)

I understand the difference between loudness and amplitude, to the point that loudness is our perception whereas amplitude is is physical property as such (this stuff is so hard to write!!)

ANYWAY! The point is this. There are config diagrams for how to set up your DX synth in terms of "frequency" and "Output". for the square wave the frequecy is as you would expect it, but on the diagram the Output (now does that mean Amp or Db or whatever, I don't know) has the numbers...

99
87
79
75
72
71

those numbers obviously don't tie up with the theory in my head. Yet, when I put them in it looks and sounds quite like a squarewave, and if I use the numbers

100
33
20
...
ect...

It sounds like a brighter sine wave.

What I want to know is on my FM7, is it refering to Db or something? Why are the numbers like that, I am confused.

p.s. sorry for the piss poor clarity in the message whenever I try to write about this stuff it comes out crappy.

Oh and just another point to add, when I listen to the third harmonic it certainly does not sound a fifth the amplitude of the first, it is far too loud to my mind.

[C00kie]

The numbers probably work for an original Yamaha DX7. These numbers are merely numbers between 0 and 99 (or was it 100??) that can be controlled with the "data" fader. Probably they have some corellation with dB's, but it's just a number on a scale from min to max.

The scale on another FM synth may be totally different. Also, on some FM synths you can just set the operator to generate block waves instead of a sine

Hope that answers your question...

[Equilibrium]

The whole manual is built for any of the DX series synths, he says that at the start. It would suprise me if the FM7 worked in a different way TBH. He also said all the examples are built only using sine waves.

The FM7 being quite a scientific instrument in many respects so I can't see that the dial would correspond to nothing. I have no understanding of Db's but from the numbers there could anyone say if that is enough information to tell you if it is Db's that is being refered to?

[Hovmod]

The intervals between the first numbers do not correspond perfectly with dB, but they are sort of almost close, which leads me to believe that cookie is correct - these are "just numbers" in the sense that it's a fader that goes from 0-100, but that they've tried to make it somewhat logical. I get -13.5dB where I would expect -12dB, but I got about -18dB for another interval, which is a more normal integer-type relationship.

However, I can't get it to correspond nicely with the square wave function, where I'd want 3f at 1/3, 5f at 1/5, 7f at 1/7 and so on.

So heaven knows.
I think you're messing with "rolands", not dB.

[kritikon]

The FM7 being quite a scientific instrument in many respects so I can't see that the dial would correspond to nothing.

Nah. The numbers are simply as Cookie says - 0-99 meaning 0=lowest value, 99=highest value. It bears no relation to any physical scale, same as most other synths use 0-100 or 0-127 or whatever. In the same way that most synths cutoff dial is 0-10...they don't usually have Hz markers.

You're reading way too much into an FM synth.
The only way you'd know what actual physical numbers are (e.g. Hz or dB etc) would be to check a manual and see if there are any statistical data given - such as min and max Hz (which then means you'd have to work it out from a logarithmic scale ) I don't remember that kind of data in any DX manual (although I can check).


And I applaud your efforts at getting to know FM synthesis. But I always personally felt that was a fruitless task for FM...I gave up in the end and just fiddled with sliders on a basic-level knowledge of how it works. It's one of the reasons I gave up on FM synthesis - just too damn fiddly to get a sound from scratch (and I also personally wasn't that enamoured of the sound character either, but hey-ho, horses for courses).

I think your time is better spent just playing with knobs and sliders.

[Equilibrium]

Thanks for the responses, I have now found that later in the book he does actually say that the scale is logarithmic and does not refer to Db's.

As for Knobs and Sliders, it's just too limited for me. I think that FM sounds are just in a different league from additive synthesis. I know it's hard, but anything hard is worth learning as few people will take that road.

Just listen to the Flyn Keys on a FM7 and it all makes a lot of sense. But yes, I understand some people can be highly put off by the amount of work required to create a sound.

Thanks again for the help.

[jupiter8]

To me it sounds that you are trying to recreate a square out of 6 sines with additive sythesis!!
Simply stacking overtones with diminishing volume.

Well that is just fine , but later you say that FM are in a different league than additive.

I'm no expert on FM (far from it) but i think there must be another way of emulating a square on it.

[stefancrs]

You can do it in several ways. The easiest is probably to first emulate two sawtooths and use a phase offset to set the pulse width, like this:
square = saw1 - saw2_with_phase_offset

You can do a sawtooth by using phase feedback on a sine:
saw = sine(saw*feedback)

I'm sorry my choice of terms isn't the best, but I hope some of it makes sense anyway

[TotcProductions]

To me it sounds that you are trying to recreate a square out of 6 sines with additive sythesis!!
Simply stacking overtones with diminishing volume.

Well that is just fine , but later you say that FM are in a different league than additive.

I'm no expert on FM (far from it) but i think there must be another way of emulating a square on it.

I think he meant fm is in a different league than Subtractive synthesis (Envelope and filter based).

I could of course be wrong. But from context (the fact that he was referencing to a post about just "Fiddling with the knobs and sliders") it looks like he meant to say subtractive. He could of meant additive as well...but in reference to "additive/subtractive"...not the additive you're talking about. I think.



Oh, and when a dev puts values of 0-127 on his controls, it's usually because that's the highest MIDI output value.

peace!

[jupiter8]

I think you're wrong but i could be wrong also.
The fiddeling with knobs and sliders were someone who gave up on understanding FM and just pulled the slider to see what happened.So i believe that is a reference to FM!!!

But i could be wrong.

[Hovmod]

To me it sounds that you are trying to recreate a square out of 6 sines with additive sythesis!!
Simply stacking overtones with diminishing volume.

...uhm...that's what a square wave *is* (well, the closer to infinite amount of overtones the better...).

[jupiter8]

...uhm... Yeah but i believe there is a better way to do that in FM than simply stacking oscillators.
And since the DX7 only has six of 'em he won't get close. And he said wanted to learn FM not additive.

[vstliefhebber]

Hi,
The numbers they are giving are such because the DX series uses a logarhitmic/Exponential function (in contrast with lineair FM e.g. Big Tick Rhino has the possibility to switch between them. Just look at a screenshot of that synth and you'll notice a bright button labelled "Lin"). On p 166-170 of Chownings book you can see how they differ from (DX)synth to synth.

Cheers,

[vstliefhebber]

http://nm-archives.electro-music.com/01 ... hesis.html

[Equilibrium]

...uhm... Yeah but i believe there is a better way to do that in FM than simply stacking oscillators.
And since the DX7 only has six of 'em he won't get close. And he said wanted to learn FM not additive.

It was just about the guy in the book proving a point, and I was happy to learn it in a hands on fashion. It's not ment for practical use, FM7 has squarewave operators afterall.

I did mean subtractive synthesis as well, and that's just an opinion and all that.