The voltage threshold for triggering a voltage-controlled oscillator (VCO) in frequency modulation (FM) synthesis can vary depending on the specific design of the synthesizer and its components. In FM synthesis, a VCO's frequency is modulated by another signal (often referred to as the modulating signal) that is applied as a control voltage.
The voltage threshold for triggering the VCO would typically refer to the minimum control voltage required to start the oscillator's operation. This threshold voltage can vary based on factors such as the design of the VCO circuit, the specific voltage range of the synthesizer, and the desired operational characteristics.
In some synthesizers, the VCO might have a specific voltage range (e.g., 0 to +5 volts), and the threshold voltage could be close to the lower end of this range, ensuring that the VCO starts oscillating as soon as the control voltage exceeds the threshold.
It's important to note that the precise details can vary between different synthesizers and manufacturers. If you're working with a specific synthesizer module or circuit, it's recommended to consult the manufacturer's documentation or specifications to determine the exact voltage threshold for triggering the VCO in FM synthesis.