Characteristic Impedance is an electrical property of a cable that describes how it opposes the flow of a high-frequency signal.

When a cable is long or when the signal it carries has a very high frequency (as in digital audio or video), it behaves like a "transmission line". Characteristic Impedance is the "resistance" that the signal encounters as it travels through that line.

Think of it as the density of the medium through which a wave propagates.

For the wave to travel smoothly and without interruption, it needs to enter and exit the transmission line without encountering a sudden change in density. To ensure a clean and lossless signal transfer, the impedance of the equipment sending the signal, the characteristic impedance of the cable, and the impedance of the equipment receiving the signal must be equal. This is called "terminating" the connection. If the impedances are not matched, some of the signal energy will be reflected back by the cable end, like a wave hitting a wall. These reflections interfere with the original signal, causing errors, jitter, and degradation of digital audio quality. Common Examples 75 Ohms: Standard for S/PDIF digital video and audio (using coaxial/RCA cables). 110 Ohms: Standard for AES/EBU digital audio (using XLR cables) and Ethernet network cables.