Retro Synth FM oscillator in Logic Pro for iPad

The synthesizer oscillators are used to generate the basic tonal color. This signal is then sent to other parts of the synthesizer engine for shaping, processing, or manipulation. See filter controls, amp and effect controls, modulation, and global and controller settings.

In FM synthesis, the basic sound is generated by setting different tuning ratios between the modulator and carrier oscillators. You can set the level of overtones created by this process.

At the core of the Retro Synth FM synthesis engine, you’ll find a multiwave modulator oscillator—controlled with the FM Shape slider, and a sine wave carrier oscillator—controlled with the FM Intensity slider. 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, thus changing the tonal color.

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

You can make fine changes to the tuning ratio of the two oscillators (and therefore the levels of the harmonics) by adjusting the FM Harmonic and FM Inharmonic controls.

FM synthesis is noted for synthetic brass, bell-like, electric piano, and spiky bass sounds.

FM oscillator parameters

FM Intensity slider and field: The carrier waveform is a simple sine wave. Drag up to add harmonics.
Harmonic/Inharmonic sliders and fields: Precisely change the levels of these sonic elements, and therefore, the tonal color of your sound. Technically, you’re changing the tuning ratio between the carrier and modulator oscillators, resulting in harmonic or inharmonic content becoming more or less audible. This parameter is also available as the Wave Variation (FM Harmonic) real-time modulation target. See Retro Synth global and controller settings.
Note: The harmonic complexity can change significantly when you adjust the (Wave) Shape slider, so avoid using it if making a subtle alteration to the harmonic or inharmonic content of your sound.
FM Shape slider and field: Change the carrier and modulator waveform. This control and the FM slider interact as you adjust either, resulting in a range of tones with more or less harmonic/inharmonic content.

FM oscillator modulation and mix parameters

Shape Mod knob and field: Choose a modulation source (LFO or Filter Envelope), and set the modulation intensity. This modulates the target chosen with the FM/Harmonic switch.
Osc Env Target pop-up menu: Choose a modulation target—FM Intensity, Harmonic, or both—for the LFO or Filter Envelope.
- FM: This lets you use the LFO or Filter Envelope to modulate the FM Intensity.
- FM+Harmonic: This lets you use the LFO or Filter Envelope to modulate the FM Intensity and Harmonic content at the same time.
- Harmonic: This lets you use the LFO or Filter Envelope to modulate the Harmonic content.
Vibrato Depth knob and field: Rotate to set the amount of vibrato (pitch modulation).
Oscillator Mix slider and field: Crossfade (set the level relationships) between the modulator and carrier oscillators.

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Logic Pro User Guide for iPad

Retro Synth FM oscillator in Logic Pro for iPad

FM oscillator parameters

FM oscillator modulation and mix parameters