Gamecube controller (or DDR Mat) to CV. Install "Nintendo" in arduino library-manager. Attach a DAC to pin 5 for CV out (like this: https://create.arduino.cc/projecthub/Arduino_Scuola/build-a-simple-dac-for-your-arduino-4c00bd)

gcpadcv.ino

// attach your DAC to this pin
#define DAC_PIN 5

#include "Nintendo.h"

// Define a Gamecube Controller
CGamecubeController GamecubeController(7);

void setup() {
  pinMode(DAC_PIN, OUTPUT);
}

void loop() {
  // Try to read the controller data
  if (GamecubeController.read()) {
    auto report = GamecubeController.getReport();

    // do things with report.a, report.b, report.x, report.y, etc
    // I'm not sure what buttons/axis are hooked to what pads, but here is an example:
    if (report.a) {
      analogWrite(DAC_PIN, 127); // 0 - 255 for 0V - 5V
    } else {
      analogWrite(DAC_PIN, 0);
    }
  }
}