10.6

Table Of Contents
218Logic Pro Instruments
In pure FM synthesis, the frequency of one signal generator, or oscillator, is altered
(modulated) by another signal generator. Positive values from the second generator
increase the frequency of the first generator. Negative values decrease the frequency.
In a synthesizer, this type of modulation takes place in the audible range. Depending on
the design of the instrument, you can hear the signals of either the first oscillator alone
(being modulated by the other oscillator), or both oscillators. The interaction between the
two generators alters the waveform signal of the first oscillator and introduces a number
of new harmonics. This harmonic spectrum can then be used as the source signal for
further sound processing, such as filtering, envelope control, and so on. See Frequency
modulation (FM) synthesis for further information.
In ES2, the frequency of oscillator1 (with a sine wave chosen—11 o’clock position for the
Wave knob) can be modulated by the output signal of oscillator2.
When oscillator2 outputs a positive signal, the frequency of oscillator1 increases.
When oscillator2 outputs a negative signal, the frequency of oscillator1 decreases.
The net effect of speeding up or slowing down the frequency of oscillator1 in each
waveform cycle is a distortion of the basic wave shape. This waveform distortion also has
the side benefit of introducing a number of new, audible harmonics.
Important: The impact of any frequency modulations you perform depends on both the
frequency ratio and the modulation intensity of the two oscillators.
The “pure” FMsynthesis method uses a sine wave for both the first and second signal
generator (both oscillator1 and 2 would be limited to generating a sine wave in ES2 if
you stuck with this approach). ES2, however, provides 100Digiwaves and countless
combinations of modulation intensities and frequency ratios that can be used for either
oscillator. This provides a vast pool of harmonic spectra and tonal colors for you to
experiment with.
Tip: The type of modulation that occurs can vary significantly when different waveforms
are chosen for oscillator2—the modulating oscillator—in particular.
Set the frequency ratio and adjust the modulation intensity
1. In Logic Pro, adjust the Frequency (coarse and fine tune) parameter values of one, or
both, oscillators.
2. Click (or drag) in the control range between the Sine and FMicons around the
oscillator1 Wave knob.
This determines the amount, or intensity, of frequency modulation.
Use ring modulation in Logic Pro ES2
Ring modulation is a powerful tool for the creation of inharmonic, metallic, bell-like sounds.
The spectra resulting from its use are inharmonic at almost every frequency ratio. The ring
modulator is a device that dates back to the early days of the synthesizer.