Page 1 of 1

Noob question: Oscillator vs. Operator

Posted: Wed Oct 01, 2008 12:51 am
by Envergure
What's the difference between an "oscillator" in subtractive synthesis and an "operator" in FM?

Re: Noob question: Oscillator vs. Operator

Posted: Wed Oct 01, 2008 1:25 am
by Synthaholic
An oscillator creates a waveform, which then (in a typical subtractive synth) goes into a filter, then an amplifier, and eventually to the audio outputs. On most synths, each voice consists of either 1 or 2 oscillators (or 3 in some cases like the Minimoog) feeding through a mixer into a single filter and VCA per voice.

An operator on an FM synth is (a digital representation of) an oscillator, envelope generator and amplifier (controlled by the envelope generator). The operator acts either as a carrier (makes a sound) or a modulator (which modulates another operator). The EG/amplifier for each operator is independent of each other (operators don't share a "VCA" like on a subtractive synth). FM synths generally have 6 operators (DX7 and its cousins), or 4 (DX11/9/21/100) per voice.

To go a step further, let me define a "partial" as used in the Roland D-50. A partial is the D-50's version of an operator, consisting of either a VA-style oscillator+lowpass filter, or a PCM wave generator, along with the digital amplifier (digital version of a VCA) and associated envelopes. Two partials are combined to make a tone (either in parallel, or one ring modulating the other), and a patch can consist of 1 or 2 tones (so, up to 4 partials). So, unlike a typical analog synth, the D-50's partials don't share filters, EGs or amplifiers.

Re: Noob question: Oscillator vs. Operator

Posted: Wed Oct 01, 2008 3:00 am
by nuromantix
Whilst the previous post is correct, a simple answer would be: they are the same thing - "Operator" is simply what Yamaha decided to call the oscillators in its 80s FM synths.

Re: Noob question: Oscillator vs. Operator

Posted: Wed Oct 01, 2008 5:18 am
by xpander
first, in FM as used by Yamaha (which is really phase modulation) it actually isn't using oscillators- scanned wavetables if i remember. second, Yamaha is describing these "oscillators" as used in the context of a greater mathematical function therefore operator is a correct mathematical label.

the real reason is mainly the first- FM synths hit when digital was big & new & especially not analog- so emphasizing that it didn't use oscillators (although "virtually" equivalent) was a selling point- it was different & new & digital.

Re: Noob question: Oscillator vs. Operator

Posted: Wed Oct 01, 2008 9:34 am
by RedElectricMoon
Whilst the previous post is correct, a simple answer would be: they are the same thing - "Operator" is simply what Yamaha decided to call the oscillators in its 80s FM synths.
It's not. Operator is a lot more than oscillator as Synthaholic said. A single operator is like the whole synth in itself from oscillator, through eg to amplifier.

By the way, some ppl say they prefer 4 operator synths to 6 operators because:
a) 4 ops are easier to program
b) they sound different
c) they have other waveforms than sines too.

*a) the principle is the same in 6 and 4 op synths, 4 op synths usually offer less choice of values for different parametres (less capable microprocessors) resultng in narrower sound palette.

*b) 6 ops can be programmed to sound the same as 4 ops - you can leave the remaining two operators inactive.

*c) If you do 4 ops sounds on a 6 ops synth, you have 2 ops free. With two ops you can create the remaining waveforms (saw, pulse, square, triangle) that arent available directly. You can use them in stacks as an audio source or a modulator. So it is not true that a DX7 cannot, for example, modulate a sine wave by a saw wave.

Re: Noob question: Oscillator vs. Operator

Posted: Wed Oct 01, 2008 10:36 am
by Jack Spider
William's video explains things well:

http://insidesynthesis.blogspot.com/200 ... art-1.html

Re: Noob question: Oscillator vs. Operator

Posted: Wed Oct 01, 2008 10:55 am
by CS_TBL
The bottom line is that FM is cool, regardless of whether you want oscs or ops!

FM is like a violin: a b***h to learn, a joy to play.

Re: Noob question: Oscillator vs. Operator

Posted: Thu Oct 02, 2008 12:17 am
by Envergure
xpander wrote:first, in FM as used by Yamaha (which is really phase modulation) it actually isn't using oscillators- scanned wavetables if i remember. second, Yamaha is describing these "oscillators" as used in the context of a greater mathematical function therefore operator is a correct mathematical label.
Thanks! That makes sense to me.
CS_TBL wrote:FM is like a violin: a b***h to learn, a joy to play.
lol nice one!

Re: Noob question: Oscillator vs. Operator

Posted: Thu Oct 02, 2008 1:02 am
by Gregor Samsa
The difference between an oscillator and an operator for me was about half a bottle of aspirin. I got rid of my dx- never could get a decent grip on it.

Re: Noob question: Oscillator vs. Operator

Posted: Thu Oct 02, 2008 1:31 am
by urbanscallywag
xpander wrote:it actually isn't using oscillators- scanned wavetables if i remember.
Why isn't a phase accumulator and a lookup table considered an oscillator?