CV Input Signal Types #8 — Macro Parameter

Description

Macro parameters are general-purpose CV inputs that control sound-shaping parameters of a module. The term "macro" emphasizes that a single parameter often affects multiple internal sonic aspects simultaneously.

Typically, the CV is combined with a potentiometer at the module — either analog (op-amp adds pot voltage and CV) or digital (pot and CV are read separately, addition in firmware). The digital method is more flexible for a generic module.

Use Cases

• Control timbre (timbre, harmonics, morph)
• Granular parameters (position, size, density)
• Wavefolder amount
• Filter resonance
• Effect parameters (delay feedback, reverb size)

Eurorack Examples (Mutable Instruments)

• Plaits: HARMONICS, TIMBRE, MORPH — three macro parameters with CV inputs + attenuverter
• Clouds: POSITION, SIZE, DENSITY, TEXTURE — four macro parameters
• Rings: BRIGHTNESS, DAMPING, POSITION

Hardware Implementation

Input Stage: OpAmp → Mux → ADC

• 1% resistors sufficient
• R_in=100k, R_ref=200k, R_fb=33k (standard -5V..+5V stage)
• Anti-aliasing: 470pF across R_fb (f_c ≈ 10kHz) — sufficient for slow modulation
• Clipping note: Signals >5V will be clipped.

Attenuverter Implementation (digital)

In Eurorack, macro CV inputs almost always have an attenuverter (attenuate + invert). Implemented digitally:

• Read potentiometer via separate mux channel
• Apply pot value as scaling factor (-1.0 to +1.0) to the CV
• Add result to base parameter value

Firmware Requirements

• Adaptive filtering (slew limiting): Smooth heavily when change is small (ADC noise/pot jitter), smooth lightly when change is large (real modulation). Better than a fixed IIR coefficient, since fast modulations are not dampened.
• Scaling: Map CV range to internal parameter range (e.g., 0..1.0 or -1.0..+1.0)