Wednesday, 21 February 2007

FM Part 2

Making a simple FM synth, part 2: adding a second oscillator (operator in FM-speak) to drive the frequency of the carrier up and down.

This video shows the impact of frequency modulation on the carrier's timbre (tone).

Watch the video

  • (0:20) In subtractive synths, and in Reaktor, tone-generating modules are often called oscillators. In FM, they're called operators. A carrier operator is an operator whose output you listen to... a modulator operator is an operator used primarily to modulate the frequency of a carrier.
  • (0:58) The modulator's A input defines its amplitude - how loud it is. normally, you'd expect an oscillator's amplitude to be somewhere in the range 0 ... 1. But we want to generate a signal to drive the carrier's frequency up and down, and we're going to be using some big numbers (in the hundreds and thousands), so I'll be using quite large values for the modulator's amplitude...
  • (1.22) "65 times every second:" MIDI note 36 is the pitch of my low C note; the 36th key on the longest possible MIDI keyboard. That corresponds to an oscillator's waveform cycling... or a piano string vibrating... at 65.4Hz (65.4 cycles per second, its frequency). Any number passed to an oscillator's F input will be added to its frequency. What we're doing here is adding the modulator's output, scaled up by some amount, to the carrier's frequency.

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