DIY synth questions

[danielwarner]

I'm growing more curious as to how synths are engineered, how circuits function, the math behind it all, etc, and I've got various questions, like for starters:

What is the difference between an oscillator and a function generator? As far as I know they both create waveforms that can be in the audio or low frequency range...

[Taylor]

I don't think there's any difference. A function generator is an oscillator, usually used as test equipment in building and repairing other instruments/processors. So the only difference is the way it's packaged and the type of control it offers, which will be tailored to test equipment uses, rather than for playing music.

[Rykhaard]

A main difference between an oscillator and function generator as well, would be if the oscillator is voltage controllable.

(It does get more technical than that, in their functionality, but the term 'voltage controllable' is for the voltage controlled oscillator's users. It gives us the ability to change the frequency of the VCO from the front panel or from another external device.)

[danielwarner]

At first I thought they were the same... then I was reading about Thomas Henry's Quadrature Function Generator, and Scott Stites writes "The problem with quadrature oscillators is frequency and amplitude stability often can fall short of expectation. What was needed was a more stable *function generator* capable of generating quadrature waveforms."

And the way it is worded implies there is a difference between an oscillator and a function generator... and it's voltage controlled, to boot!

[EdisonRex]

A function generator (as defined above) strives for clinical accuracy and stability.

In that paradigm, function generators are oscillators, but they are a piece of test equipment really. Function generators are oscillators, of course.

"VCO" or "DCO" as Ryk mentioned implies external controllability. A function generator could be a VCO or more likely a DCO.

Also a function generator in its purest sense is a generator of periodic functions. You'll find those sorts of terms used instead of "oscillator" in certain families of synthesizers, especially where the periodic functions go from subaudio to ultraaudio, or are fairly complex functions (a sequencer is a function generator, as is an envelope generator).

Which gets us to the word "function". It'd be a mathematically describable function; or arbitrary function (in the case of a random CV generator) or sequencer (a series of arbitrary linear functions).

So depending on how you look at this, a function generator is a subset of oscillators, or oscillators are a subset of function generators. I favour the latter definition myself.

[wmonk]

Mathematically, a function depends on parameters. Translating that to synths, I would say the difference between a function generator and a oscillator are that the latter only depends on a variable (the frequency control) and the function generator also on some parameters (skew comes in mind, or attack and decay times). Actually, a lot of the so called function generators can work looped (thus being an oscillator) or one shot, more like an envelope generator.

[danielwarner]

Thanks for the replies! I think I get it now

[Thomas_Henry]

Hi All,

I should have jumped in on this sooner.

An oscillator is a filter whose regeneration is sufficiently high to permit continued ringing. The output is sinusoidal.

A function generator is a Schmitt trigger-integrator affair. Its output is a triangle (or square, if you tap the Schmitt trigger).

Either one can be voltage controlled. In the context of the quote mentioned above, a function generator is usually more stable and the amplitude of its waveform doesn't change appreciably with a change in frequency.

Thomas Henry