Octave per Volt (oct/V) in Voltage-Controlled Oscillators

VCOs are electronic circuits that generate periodic waveforms, such as sine, square, or triangle waves, whose frequency can be controlled by an input voltage. To describe the relationship between the control voltage and the resulting frequency, a parameter called “octave per volt” (oct/V) is often used.

1. The Basics of VCOs: Voltage-Controlled Oscillators are widely employed in synthesizers, electronic music instruments, and frequency modulation systems. They consist of a voltage-sensitive element, typically a capacitor or inductor, and a feedback mechanism to sustain oscillation. The control voltage applied to the VCO circuit determines the output frequency.
2. Octave per Volt (oct/V) Defined: Octave per Volt (oct/V) is a measure of the sensitivity or tracking ability of a VCO to changes in the control voltage. It quantifies the amount of frequency change, in octaves, for each volt of variation in the control voltage. The oct/V value specifies the scaling relationship between the control voltage and the resulting frequency.
3. Relationship to Musical Octaves: In music theory, an octave represents a doubling or halving of frequency. Moving up or down one octave corresponds to doubling or halving the frequency, respectively. The oct/V parameter in VCOs refers to how many octaves the frequency will change per volt of control voltage.
4. Adjusting Frequency with Oct/V: By understanding the oct/V value, musicians and sound designers can precisely control the pitch and musical intervals of VCO-generated waveforms. For example, if a VCO has an oct/V value of 1, a 1-volt increase in the control voltage will cause the output frequency to shift up by one octave.
5. Calibrating VCOs: To achieve accurate and consistent pitch tracking, VCOs often require calibration. Calibration involves adjusting the circuit to match the desired oct/V value. By calibrating a VCO, it can accurately follow the intended frequency changes based on control voltage variations.
6. Design Considerations: The oct/V parameter is an important design consideration for VCO circuits. Different VCO designs may exhibit different sensitivities, offering varying oct/V values. The chosen oct/V value impacts the range and resolution of frequency control provided by the control voltage. Higher oct/V values provide a wider frequency range per volt, while lower oct/V values offer a more precise and fine-tuned control.
7. Voltage Modulation Applications: The concept of oct/V extends beyond VCOs and finds applications in various voltage modulation systems. It plays a crucial role in voltage-controlled filters, voltage-controlled amplifiers, and other voltage-dependent modules used in sound synthesis and audio processing.

Octave per Volt (oct/V) is a fundamental parameter that defines the scaling relationship between control voltage and frequency in Voltage-Controlled Oscillators. It allows musicians and sound designers to precisely control the pitch and intervals of VCO-generated waveforms. Understanding oct/V aids in the calibration and design of VCO circuits, enabling accurate and versatile frequency modulation. This parameter’s influence extends beyond VCOs and finds relevance in other voltage modulation applications within the realm of sound synthesis and electronic music.

Arduino code – frequency oct per volt as a function

An example Arduino code generates a frequency output based on the oct/V (octave per volt) parameter.

// Octave per Volt (oct/V) Arduino Code
// Generates frequency based on control voltage

const int controlVoltagePin = A0;   // Analog input pin for control voltage
const int outputPin = 9;            // Digital output pin for generating frequency

float octPerVolt = 0.5;             // Octave per Volt value (adjust as needed)
float referenceVoltage = 5.0;       // Reference voltage of the Arduino (adjust as needed)
float baseFrequency = 440.0;        // Base frequency in Hz (adjust as needed)

void setup() {
  pinMode(outputPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int controlVoltage = analogRead(controlVoltagePin);   // Read control voltage from analog input
  float voltage = controlVoltage * (referenceVoltage / 1023.0);  // Convert analog value to voltage
  float frequency = baseFrequency * pow(2.0, (voltage * octPerVolt));  // Calculate frequency based on oct/V

  tone(outputPin, frequency);    // Generate the frequency output

  Serial.print("Control Voltage: ");
  Serial.print(voltage, 2);      // Print control voltage value to two decimal places
  Serial.print("V, Frequency: ");
  Serial.print(frequency, 2);    // Print frequency value to two decimal places
  Serial.println("Hz");

  delay(500);
}