Frequency Modulation

This applet uses FM to create a variety of sounds. Each row has a sine wave oscillator.

To do:

  • Wait for separate editor window to appear. (Note: The envelope editor may not appear on some computers.)
  • Select instruments from the menu such as Bell or Clarinet. Click the Play Keys button. Play the keyboard to hear notes.
  • Select Simple instrument. Uncheck box labeled 1 to hear carrier with no modulation. Check it again to turn on modulation.
  • Change the Index in the second row to increase or decrease the amount of modulation.
  • Change the freqMult in the second row to change the frequency ratio. Try typing in a new value and hit Enter.


  • Hear—check this to hear the output of an oscillator.
  • 1,2,3,4—check one of these to request modulation by another oscillator.
  • Sust—check this to cause the envelope to stick on the second point and sustain its level.
  • Fixed—check this to use a fixed frequency for an oscillator. Otherwise the frequency will be determined by playing keys on the keyboard.
  • EnvelopeEditor—move points, or add new points to shape an oscillator’s amplitude. Shift-click a point to remove it.
  • frequency—set frequency of oscillator in Hz. (FixedFreq must be checked.)
  • freqMult—scale the frequency from the keyboard by this amount. (FixedFreq must be unchecked.) Controls the "carrier:modulator ratio."
  • depth—scale the amount of modulation input. Normally set to 1.0.
  • index—amount of modulation is "index * modulatorFrequency."
  • amplitude(DB)—controls loudness in decibels.

Instrument Notes:

  • Bell—Op#0 modulated by Op#1. Envelopes decay rapidly like a bell. FreqMult set to "1.4," which gives complex enharmonic spectrum.
  • Brass—uses "sustain" to hold note while key pressed. Vibrato provided by Op#2 has delayed start because of envelope rising late. Vibrato frequency set to fixed low value by checking Fixed box. Vibrato frequency does not change with key pressed.
  • Trumpet - you can hear output of Ops 1, 2, and 3. Ops 2 and 3 provide slightly detuned harmonics. Vibrato from Op#3.
  • Woozy - slowly rising modulation envelope provides "wah"-like sound.