3

Chapter 14 Ultrabeat 342
Use 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’s range of 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 rst 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 rst oscillator alone (being
modulated by the other oscillator), or both oscillators. The interaction between the two
generators alters the waveform signal of the rst 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 ltering, envelope control, and so on. See Frequency modulation (FM)
synthesis on page 493.
In Ultrabeat’s FM synthesis mode, oscillator 1 (the carrier) generates a sine wave. The frequency
of oscillator 1’s 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 eect 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 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 knob
FM Amount can be modulated by the sources shown in the mod and via pop-up menus. See
Ultrabeat modulation overview on page 360.