Apple Logic Express 7 - Manual (Page 84)

84 Chapter 13 EFM 1
Modulator and Carrier
Harmonic
In FM synthesis, the basic overtone structure is determined by the tuning relationship
of the Modulator and Carrier. This is often expressed as a tuning ratio. In the EFM 1, this
ratio is achieved with the Modulator and Carrier Harmonic controls. Additional tuning
control is provided by the Fine (Tune) parameters.
You can tune the Modulator and Carrier to any of the first 32 harmonics. The tuning
relationship (or ratio) greatly changes the base sound of the EFM 1, and is best set by
ear.
As a rule of thumb: even tuning ratios tend to sound more harmonic or musical, while
odd ratios produce more inharmonic overtones—which are great for bell and metallic
sounds.
As an example, the Modulator and Carrier set to the First Harmonic (a 1:1 ratio) will
produce a sawtooth-like sound. If the Modulator is set to the Second Harmonic, and
the Carrier to the First Harmonic (a 2:1 ratio), the tone produced will sound similar to a
square wave. In this respect, the tuning ratio is somewhat similar to the waveform
selector of an analog synthesizer.
The Harmonic dial of the EFM 1 Carrier can be set to a value of zero. This, in effect,
produces a DC (Direct Current) signal. In this scenario, the Carrier actually acts as a
wave shaper.
Fine
Fine tune adjusts the tuning in-between two adjacent harmonics (as determined by the
Harmonic control). The range of this control is ±0.5 harmonic. Dependent on the
amount of detuning, this will create either a subtle “beating” of the timbre or—if high
detuning amounts are used—adds new harmonic and inharmonic overtones.
In the center (0) position Fine tune does not have an effect. You can easily center the
Fine tune control by clicking on the 0.
Fixed Carrier Button
This button allows you to disconnect the carrier frequency from keyboard, pitchbend,
and LFO modulations.