“AC coupled” refers to a type of input or output connection in which only the alternating current (AC) component of a signal can pass through, effectively blocking any direct current (DC) component present in the signal. This is typically achieved by using a capacitor in series with the signal path, which allows AC signals to pass while blocking DC signals.
In synthesizers and other audio processing equipment, AC coupling is often used in audio input and output stages, as well as in certain signal processing circuits. The primary purpose of AC coupling is to remove any DC offset that may be present in the signal, ensuring that the output signal is centered around a zero-volt baseline. This can help prevent issues such as unwanted clicks, pops, or distortion that can occur when mixing or processing signals with a DC offset.
However, it is important to note that AC coupling may not be suitable for all types of signals in a modular synthesizer system, particularly control voltage (CV) signals, which often contain both AC and DC components. Using an AC-coupled input for CV signals may result in a loss of information or unintended signal alterations. In these cases, it is preferable to use DC-coupled inputs and outputs, which allow both AC and DC components of a signal to pass through unaltered.