Working with the EFM1 Modulator and Carrier Parameters

In FM synthesis, the basic sound is generated by setting different tuning ratios between the Modulator and Carrier oscillators, and by altering the FM intensity. The tuning ratio determines the basic overtone structure, and FM intensity controls the level of these overtones.

At the core of the EFM1 synthesis system, you’ll find a multi-wave modulator oscillator and a sine wave carrier oscillator. The basic sine wave (of the carrier oscillator) is a pure, characterless tone.

To make things more sonically interesting, the modulator oscillator is used to modulate the frequency of the carrier oscillator. This modulation occurs in the audio range (you can actually hear it), and results in a number of new harmonics becoming audible.

The pure sine wave (of the carrier oscillator) is combined with the newly generated harmonics, making the sound much more interesting.

Changes to the ratio of the two oscillators is achieved by adjusting the Harmonic parameters, found in both the Modulator and Carrier sections. Additional tuning control is provided by the Fine (Tune) parameters, discussed below.

Figure. Modulator and Carrier parameters.
  • Harmonic knobs: Set the tuning ratio between the Modulator (left) and Carrier (right) oscillators. See Setting the EFM1 Tuning Ratio.
  • Fine (tune) knobs: Adjust the tuning between two adjacent harmonics (as determined by the Harmonic knobs). The range of this control is the center (0) position, Fine tune does not have an effect. Click the “0” to center the Fine tune knob. Dependent on the amount of detuning, you will hear either:  
    • A subtle “beating” of the timbre-if lower detuning amounts are used.

    • New harmonic and inharmonic overtones-if high detuning amounts are used.

  • FM (Intensity) knob: Sets the amount of carrier oscillator frequency modulation by the modulator oscillator. As you adjust the FM knob, the intensity (and number) of newly generated overtones (harmonics) increases-making the sound brighter.

    Note: Although the technology behind it is very different, you could compare the FM (Intensity) parameter with the Filter Cutoff parameter of an analog synthesizer.

  • Wave knob (Modulator): Chooses a different waveform for the modulator oscillator. See Choosing a Different EFM1 Modulator Waveform.
  • Fixed Carrier button (Carrier): Enable to disconnect the carrier frequency from keyboard, pitch bend, and LFO modulations. This allows you to produce a carrier tone that is free of these modulation sources.

Setting the EFM1 Tuning Ratio

The carrier frequency is determined by the played key, and the modulator frequency is typically a multiple of the carrier frequency.

You can tune the modulator and carrier to any of the first 32 harmonics. The tuning relationship (or ratio) between the two significantly changes the base sound of the EFM1, and is best set by ear.

The Harmonic knobs are used to set the tuning ratio between the Modulator (left) and Carrier (right) oscillators.

As a rule of thumb:  even tuning ratios between the carrier and modulator tend to sound more harmonic or musical, while odd ratios produce more inharmonic overtones—which are great for bell and metallic sounds.

In this respect, you can view the tuning ratio as being somewhat like the waveform selector of an analog synthesizer.

Note: The Harmonic and Fine tune knobs only affect the tuning relationship between the Carrier and Modulator oscillators. These should not be confused with the global Tune and Fine Tune parameters, which determine the overall tuning of the EFM1 (see Adjusting Global EFM1 Parameters).

Some tuning ratio examples to try
  • Set the modulator and carrier to the first harmonic (a 1:1 ratio), and the EFM1 will produce a sawtooth-like sound.

  • Set the modulator to the second harmonic, and the carrier to the first harmonic (a 2:1 ratio), and you will produce a tone that sounds similar to a square wave.

Choosing a Different EFM1 Modulator Waveform

In classic FM synthesis, sine waves are used as modulator and carrier waveforms. The EFM1 Modulator oscillator provides a number of additional digital waveforms, which extend its sonic capabilities significantly. These waveforms contain a number of additional harmonics which add a new level of richness to the resulting FM sounds.

To choose a different waveform
  • Turn the Wave parameter knob.

  • At the full left position, the modulator produces a sine wave.

  • As you turn the Wave parameter clockwise, you will step/fade through a series of complex digital waveforms.