10.6

Table Of Contents
568Logic Pro Instruments
Use Logic Pro Ultrabeat oscillator 1 FM mode
FM(frequency modulation) synthesis is well suited for creating bell-like digital tones and
metallic sounds. The principle of frequency modulation (FM) synthesis was developed in the
late 1960s and early 1970s by John Chowning. It was popularized by Yamaha DXsynthesizers
in the 1980s. Although Ultrabeat can’t be compared with the DXseries in the discipline of
pure FMsynthesis, it can achieve some of the signature sounds of these 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.
In FMsynthesis mode, oscillator1 (the carrier) generates a sine wave. The frequency of the
oscillator 1 sine wave is modulated by the waveform of oscillator2 (the modulator).
When oscillator2 outputs a positive (or higher) frequency signal, the frequency of
oscillator1 increases.
When oscillator2 outputs a negative (or lower) frequency 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
introduces a number of new, audible, harmonics. The more complex the oscillator2
waveform, the more partials are created by increasing FMAmount. Watch the display to
see how the sine wave takes on an increasingly complex shape.
Important: The impact of any frequency modulations depends on both the frequency ratio
and the modulation intensity of the two oscillators.
Set the frequency ratio and adjust the modulation intensity
1. In Logic Pro, turn on FM mode for oscillator 1.
2. Turn on oscillator 2.
3. Adjust the Pitch parameter values of one, or both, oscillators.
4. Adjust the amount (intensity) of frequency modulation with the FMAmount knob.
FM Amount can be modulated by the sources shown in the mod and via pop-up menus.
See Logic Pro Ultrabeat modulation overview.