Tutorial: Programming a Synth - Frequency Modulation Explained [9/12]

Welcome back to our series on "How to Program a Synth" with our synthesizer SkyDust 3D! Let's dive into the fascinating world of Frequency Modulation (FM) synthesis.

Understanding Frequency Modulation

Frequency Modulation is a synthesis technique that involves using one waveform to modulate the frequency of another. In FM synthesis, oscillators are referred to as operators, which can be classified into two types: carriers and modulators.

• Carriers: These operators produce the sound you hear and are routed directly to the output.
• Modulators: These operators modify the frequency of the carriers, thereby altering the tone.
  
  

The Difference Between LFOs and Modulators

While Low-Frequency Oscillators (LFOs) can modulate frequency, they typically operate below 20 Hz, which is outside the audible range. FM modulators, on the other hand, function within the audible spectrum and often utilize specific ratios to create harmonic relationships with the carriers.

For instance, setting a modulator to a 0.5 ratio means it will oscillate at half the frequency of the carrier. This ensures a tonal connection between the two, which is key to creating musically pleasing sounds.

Practical Application with SkyDust 3D

Let’s walk through a practical example using SkyDust 3D. We'll start by manipulating the Init Preset:

1. Initialize the Preset: Go to the FM page, remove all oscillators except the first one, which will act as our carrier.
2. Set the Modulator: Designate the second oscillator as the modulator. Adjusting the ratio of this oscillator will change the tone of the first.
   

If we set the modulator's ratio to 4, it will oscillate four times faster than the carrier. The modulation gain determines how much the modulator influences the carrier’s tone.

• Ratio of 4: The second oscillator plays at four times the frequency of the first.
• Modulation Gain: Adjusting this gain will show how intensely the modulator affects the carrier’s sound.

To create a key-like sound, we start with a bright attack:

1. Oscillator Setup: Use the first oscillator with a super short attack (0 ms) and a short release. The second oscillator, acting as the modulator, should mirror these settings.
2. Adjust Ratio for Brightness: Set the ratio of the second oscillator to 6 for a bright attack. Increase the octave for a higher frequency.

By fine-tuning these settings, we can achieve a sound reminiscent of a hammer striking a key.

Next, we add more oscillators to enrich the tone:

1. Additional Carriers and Modulators: Use a third oscillator as a new carrier and a fourth as its modulator. Set a 0 ms attack with an 800 ms release for both, with a ratio of 3 for the modulator.
2. Creating Mellow Tones: Introduce a fifth carrier and a sixth modulator for a more mellow sound. Use an ADSR envelope with a decay of 800 ms and a sustain level adjusted for the desired tone.

To add a chorus effect, duplicate the existing oscillators without modulation but slightly detune them to create a richer, fuller sound.

Mastering FM

We’ve only scratched the surface of what Frequency Modulation can do. Experimenting with different ratios, modulation gains, and oscillator settings can lead to a wide variety of sounds. In the next article, we'll continue to refine the tone of these keys using other features of SkyDust 3D. 

Happy synthesizing!

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