Make Your FM Synth Sound Interesting with External Modulation Magic

In the vast world of sound design, Frequency Modulation (FM) synthesis stands as a formidable player. Its capacity to generate rich timbres and evolving sounds is unparalleled. Yet, despite the range of sonic textures FM can achieve natively, there’s a novel horizon for exploration when we combine external modulation sources with FM patches. These sources introduce an external dynamism that can augment, transform, or elevate the existing potential of FM synthesis.

The Essence of FM Synthesis

Before delving deep into the incorporation of external modulation, a brief touch on FM synthesis is essential. FM synthesis involves modulating one waveform (the carrier) with another waveform (the modulator). The depth and rate of this modulation determine the resulting timbre. At its core, FM synthesis is about motion and change, making it a perfect candidate for external modulation sources.

Korg Volca FM 2, a popular FM synthesizer

The Charm of External Modulation

Understanding Modulation Sources

In an FM environment, modulators are typically oscillators within the synthesizer. However, when we refer to “external modulation sources,” we’re looking beyond the confines of the instrument. These could range from:

  1. Control Voltage (CV) Devices: Hardware units that generate or process control voltage signals.
  2. Sequencers: Devices that send step-wise or pattern-based control changes.
  3. Expression Pedals: Foot-operated devices that vary a control signal based on the pedal’s position.
  4. Other Synthesizers: Using one synth to modulate parameters on another.

Dynamics and Evolution

When you interlink FM synthesis with external modulators, you’re introducing an element of unpredictability and organic evolution. A static FM patch, regardless of its richness, can eventually become predictable over time. However, an external sequencer or a random CV generator can breathe new life into it, making the sound evolve, morph, and flourish in unexpected ways.

Incorporating External Sources: Practical Approaches

1. CV Modulation

Control Voltage is a staple in modular environments. By routing a CV signal from an external device into an FM synthesizer’s input, one can modulate various parameters of the FM patch.

Example: Consider a scenario where an FM patch utilizes a simple sine wave as the carrier and modulator. When you introduce a slow LFO from an external modular system into the FM depth, the result is a dynamic shift in timbres – ranging from subtle nuances to drastic sonic transformations based on the LFO’s intensity and rate.

2. Sequenced Changes

Sequencers, especially those that allow per-step modulation or feature randomization, can offer a rhythmic and patterned transformation to FM patches.

Example: Using a hardware sequencer, you can design patterns that influence the modulation index of an FM patch. This would mean that over the course of a sequence, the FM depth (and thus the timbre) changes step by step, creating an evolving soundscape.

3. Expression and Real-time Manipulation

Expression pedals are not just for guitarists. They can serve as potent real-time modulation sources for FM patches.

Example: By linking an expression pedal to control the modulation frequency, a musician has direct, foot-controlled manipulation over the FM sound. This becomes especially powerful during live performances, where the intricacies of the modulation can ebb and flow with the musician’s intent.

4. Synth to Synth Modulation

Utilizing one synthesizer to modulate another may sound unorthodox, but the resulting sonic territories are vast and uncharted.

Example: A monophonic analog synth with a robust LFO section can be used to modulate the carrier frequency of a digital FM synthesizer. This fusion of analog and digital, of different synthesis methods, leads to unique tonal characters that neither synth could achieve on its own.

The Caveats

While external modulation promises endless possibilities, it’s essential to recognize its pitfalls:

  1. Over-modulation: Overdoing modulation can make sounds incoherent or too abrasive. It’s a delicate balance between movement and musicality.
  2. Compatibility Issues: Not all FM synthesizers accept external modulation gracefully. Ensure that the devices you’re interfacing are compatible in terms of voltage levels and input types.


Integrating external modulation sources with FM patches is an exercise in sonic exploration. While the foundational principles of FM synthesis are potent on their own, the external dimension adds a layer of dynamism that’s hard to ignore. As with any sound design approach, the key lies in experimentation, understanding the tools at hand, and molding them to one’s artistic vision. Whether you’re an ambient soundscape artist, a techno producer, or just an enthusiast, the fusion of external modulation with FM synthesis promises a world of uncharted sonic landscapes waiting to be discovered.

Similar Posts