S/PDIF stands for Sony/Philips Digital InterFace, it is an industry-standard interface used for consumer equipment. It transmits a serial data stream (similar to AES3) in unbalanced form over a coaxial cable. The data stream contains a stereo pair of up to 24-bit data, messages (to identify the data), status flags and synchronisation pulses (used to extract the word clock). The data stream is similar to AES3, but the status flags are different and are not entirely compatible. For reliable operation, the output stage impedance, the characteristic impedance of the cable and the load impedance at the receiver should all be 75 ohms. To avoid interference from other appliances, the screen wire must be securely connected to chassis at both ends. The interface is commonly used at sample rates up to 192kS/s over short distances (less than 5 metres). The connector type can be RCA phono or BNC. S/PDIF data can be transmitted over fibre-optic cables also.