CV Input Signal Types #12 — AM and Cross-Modulation
| Property | Value |
|---|---|
| Category | Bipolar / Modulation |
| Voltage Range | -5V..+5V |
| Polarity | Bipolar |
| Bandwidth | DC..20kHz+ (audio-rate) |
Description
Amplitude modulation (AM) and cross-modulation are techniques where one signal modulates the amplitude or an arbitrary parameter of another signal at audio rate. AM generates sidebands in the spectrum (sum and difference frequencies).
Ring modulation is a special case of AM where the carrier is fully suppressed (only sidebands remain).
Use Cases
- Ring modulation (metallic, inharmonic tones)
- Amplitude modulation (tremolo at audio rate)
- Cross-modulation (one oscillator modulates parameters of another)
- Vocoder-like effects
Eurorack Examples (Mutable Instruments)
- Warps: Dedicated cross-modulation module (ring mod, AM, wavefolder) — processes audio-rate AM/ring mod entirely digitally via internal STM32F4 ADCs
Hardware Implementation
Identical requirements to FM (audio-rate). Audio-rate bipolar, not achievable via multiplexed ADS8866.
Hybrid alternative: An analog VCA chip (e.g., LM13700, V2164) before the ADC can implement AM/ring mod in hardware without digitizing the audio signal. Modern digital modules (like MI Warps) use direct high-speed sampling via internal MCU ADCs.