AC Coupling is an electronic circuit technique that allows an audio signal (which is an Alternating Current - AC) to pass from one stage to another, while blocking any Direct Current (DC) voltage that may be present.

Think of it as a safety filter. It ensures that only the "moving part" of the signal (the audio information) passes through, while any continuous, stationary electrical voltage (which could damage equipment or alter the operation of the next stage) is blocked.

The simplest way to perform AC coupling is to place a capacitor in series with the signal. This capacitor acts as a high-pass filter with an extremely low cutoff frequency (usually below 1 Hz), effectively allowing the entire audio spectrum to pass through but blocking Direct Current (DC). AC coupling is used extensively in audio circuits to electrically isolate one stage from another, ensuring that the operating conditions of one do not negatively affect the next and protecting the components from unwanted DC voltages.