Moog Music Explores the Sonic Frontier: FM, AM and Harmonic Alchemy

The video methodically breaks down how harmonics are generated through modulation. When an audio-rate modulator interacts with a carrier oscillator, sidebands emerge—new frequencies mathematically related to the original signals. The number and strength of these sidebands depend on both the modulation depth and the waveforms involved. For instance, triangle waves, with their sparse harmonic content, yield a different spectrum of sidebands compared to sawtooth waves, which are already harmonically dense.

The Moog team explains that FM synthesis typically favours simple waveforms like sines or triangles, as these provide a blank canvas for harmonic creation. By contrast, starting with harmonically rich waveforms can quickly lead to sonic chaos. The lesson also covers how the modulation depth—how far the carrier’s frequency is pushed—affects the resulting sound, with deeper modulation producing more sidebands and, consequently, more complex timbres.

Beyond FM, the video explores AM and its unique characteristics. Unlike FM, AM always retains the carrier frequency, reinforcing the tonal centre even as new harmonics are introduced. The team demonstrates how raising an LFO into the audio range for amplitude modulation yields a distinctly different flavour, and they touch on the creative possibilities of modulating other parameters, like filter cutoff, at audio rates for further harmonic sculpting.

With the theory in place, the video shifts to practical patching on the Moog Messenger. The host walks through programming FM by routing oscillator 1 to modulate oscillator 2, with both set to triangle waves for maximum clarity. This setup produces a broad palette of FM sounds, ranging from subtle shimmer to aggressive clangour, depending on the modulation depth.

Envelope modulation is then introduced as a means to dynamically control FM depth. By assigning the filter envelope to the modulation amount, the Messenger can mimic the evolving articulations of classic ’80s and ’90s FM bass tones. Tweaking the envelope parameters yields a variety of attack and decay shapes, showcasing how modulation can breathe life into otherwise static patches.

The demonstration also touches on the interplay between FM and other forms of modulation, hinting at the layered complexity possible when combining envelope, LFO, and audio-rate sources. The Messenger’s interface is shown to facilitate these explorations, making it a flexible platform for both beginners and seasoned patchers.

The lesson pivots to the world of distortion and wavefolding, highlighting how these processes generate harmonics through non-linear means. Saturation, as found in classic Moog circuits like the CP3 mixer, introduces asymmetrical clipping, transforming a triangle wave into a more complex, square-like shape as the gain increases. This approach adds musical distortion and a wealth of new overtones.

Wavefolding, inspired by the West Coast synthesis tradition, is presented as another route to harmonic abundance. Instead of simply clipping the waveform, wavefolding bends and folds the peaks back onto themselves, creating intricate timbral variations. The Messenger’s wavefolding circuit is demonstrated, with dynamic modulation via the filter envelope adding further movement. The video encourages viewers to stack modulation sources and effects, reinforcing the idea that synthesis is as much about exploration as it is about precision.