ABOUT FM

Ok, one more Operator tip, then we’ll move on from all this algorithm alphabet soup.

This is a simple experiment to do if you haven’t fully wrapped your head around FM synthesis. I didn’t really understand the basics of FM for a long time, and going through this process really helped me.

Bear in mind before we begin we’ll be working with Operator’s default algorithm, so oscillator B modulates oscillator A.

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Start with Operator in its default state. You’ll need a nice sustained note, so you might want to take a moment to program a MIDI clip with a long note.

Then, configure oscillator B like this:

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The frequency is Fixed at 1Hz. (10Hz * 0.1)

Now, increase Level. As you do so, you’ll start to hear the pitch of oscillator A bend up and down, just like you would if you were turning up a pitch LFO. Then, with Level cranked up, start to increase¬†Freq. The pitch modulation gets faster (as if you were turning up the rate of a pitch LFO).

As you continue to increase the frequency, the character of the sound starts to change and it no longer sounds like an LFO. This is the crux of the matter. Remember, LFO stands for Low Frequency Oscillator – meaning it’s slow. When we refer to Frequency Modulation, we’re typically referring to pitch modulation that’s very fast.

When you filp the Fixed switch off, you can no longer detect the pitch modulation as such.

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In it’s default state (shown above), the frequency of oscillator B automatically matches that of oscillator A. For example, let’s say you’re playing the A above Middle C on your MIDI keyboard. Oscillator A will produce a 440Hz sine wave, while oscillator B modulates the pitch of that sine wave at a rate of 440Hz.

This tuned and very rapid pitch modulation produces musically coherent harmonics and brightens the timbre of oscillator A.