Ring Modulator

Tier: Primitives | ComponentType: 16 | Params: 5

Ring modulation and amplitude modulation with internal carrier oscillator.

Overview

RingModulator multiplies the input signal by an internal carrier oscillator. In ring modulation mode, the multiplication produces sum and difference frequencies — the classic metallic, inharmonic sound used in sci-fi effects and experimental music. In AM mode, the carrier modulates the input's amplitude envelope without creating new sum/difference partials, producing a tremolo-like effect at low frequencies and sideband tones at audio rate.

The carrier oscillator supports sine, triangle, square, and sawtooth waveforms. At sub-Hz carrier frequencies, both modes produce amplitude variation; at audio-rate frequencies, the distinction between ring mod (bilateral multiplication) and AM (unipolar modulation) becomes clearly audible.

File Locations

	Path
Header	Sources/FolioDSP/include/FolioDSP/Primitives/RingModulator.h
Implementation	Sources/FolioDSP/src/Primitives/RingModulator.cpp
Tests	Tests/FolioDSPTests/RingModulatorTests.swift
Bridge	Sources/FolioDSPBridge/src/FolioDSPBridge.mm (RingModulatorBridge)

Parameters

Index	Name	Description	Min	Max	Default Min	Default Max	Default	Unit
0	Carrier Freq	Carrier oscillator frequency	0.1	20000.0	50.0	2000.0	440.0	Hz
1	Waveform	Carrier waveform: 0=Sine, 1=Tri, 2=Square, 3=Saw	0.0	3.0	0.0	3.0	0.0
2	Depth	Modulation depth	0.0	100.0	0.0	100.0	100.0	%
3	Mode	0=Ring Modulation, 1=Amplitude Modulation	0.0	1.0	0.0	1.0	0.0
4	Mix	Dry/wet blend	0.0	100.0	0.0	100.0	100.0	%

Processing Algorithm

1. Generate Carrier

The internal oscillator ticks at the carrier frequency:

\[c = \text{osc}(\phi_c)\]

2. Ring Modulation (mode = 0)

\[y_{\text{mod}} = x \cdot c \cdot \frac{d}{100}\]

Bilateral multiplication creates sum and difference frequencies: \(f_{\text{in}} \pm f_c\).

3. Amplitude Modulation (mode = 1)

\[y_{\text{mod}} = x \cdot \left(1 + \frac{d}{100} \cdot c\right)\]

Unipolar modulation preserves the original frequency plus sidebands.

4. Dry/Wet Mix

\[y = x \cdot (1 - m) + y_{\text{mod}} \cdot m\]

Snapshot Fields

Field	Type	Range	Unit	Description
Carrier Freq	Float	0.1–20000	Hz	Current frequency
Carrier Phase	Float	0–1		Normalized phase
Depth	Float	0–100	%	Modulation depth
Waveform	Uint8	0–3		Active waveform
Mode	Uint8	0–1		Ring/AM mode
Input Level	Float	0–1		Smoothed input
Output Level	Float	0–1		Smoothed output
Mod Amount	Float	-1–1		Instantaneous modulation value

Implementation Notes

• Carrier is an internal Oscillator instance (reuses the Oscillator component)
• Level tracking uses exponential smoothing (α = 0.01) for display
• At sub-Hz carrier frequencies, both modes produce LFO-style amplitude variation
• Carrier waveform selection: square produces hard on/off gating, saw produces asymmetric modulation

Equation Summary

y = x · (1 + depth·osc(f))