CV Input Signal Types #15 — Model/Algorithm Select

Description

Model select CV is a stepped voltage that selects a discrete index — e.g., which oscillator model, which algorithm, or which waveform is active. The analog voltage value is quantized to an integer index in firmware (e.g., 0–15).

Use Cases

• Select oscillator model (e.g., 16 different synthesis algorithms)
• Waveform selection
• Preset/bank switching via CV
• Drum sound selection in a drum module

Eurorack Examples (Mutable Instruments)

• Plaits: MODEL input — CV voltage jumps through 16 oscillator models

Hardware Implementation

Standard Input Stage: OpAmp → Mux → ADC

• Identical to generic unipolar CV
• Hardware protection against overvoltage (>5V to ±12V) through single-supply op-amp (clips to 0..3.3V). Firmware must strictly clamp ADC values to the value range (0..N) to avoid integer overflows at high CV voltages.

Firmware Requirements

• Quantization: Map ADC value to N equal steps (e.g., 16 steps at 16-bit ADC = 4096 LSB per step)
• Hysteresis mandatory: Without hysteresis, the display/sound flickers at step boundaries. Implement at least ±1/4 step width as dead zone.
• Debounce for state changes: Short lockout (10–50ms) after model change. ADC continues running, but the switch is delayed to avoid audio glitches with noisy control voltages.