What interfaces are used for digital audio transmission?
S / PDIF (Sony / Phillips Digital Interface Format, a Sony and Phillips digital interface format) is a digital interface for consumer radio equipment.
AES / EBU (Audio Engineers Society / European Broadcast Union) is a digital interface for studio radio equipment.
Both interfaces are serial and use the same signal format and coding system, BMC (biphasic mark code) with automatic synchronization and can transmit signals in PCM format of up to 24 bits at sample rates up to 48 kHz.
Each sample of the signal is transmitted as a 32-bit word, in which 20 bits are used to transfer the sample and 12 bits to form the sync preamble, transfer additional information, and the parity bit. The 4 bits of the overload group can be used to expand the sample format to 24 bits.
In addition to the parity bit, the word overhead contains the validity bit, which must be zero for each valid sample. In the case of receiving a word with a single bit of Validity or with a parity violation in the word, the receiver interprets the entire sample as wrong and can choose to replace it with the previous value or interpolate based on several adjacent valid samples. Invalid readings can be transmitted by CD players, DAT recorders and other devices, if during the reading of the carrier information it was not possible to correct the errors that occurred during the reading process.
As a standard, the encoding format is intended for the transmission of a one and two channel signal; however, when the service bits are used to encode a channel number, a multi-channel signal can be transmitted.
On the electrical side, S / PDIF allows connection with a coaxial cable with a characteristic impedance of 75 Ohm and RCA connectors (“tulip”), the amplitude of the signal is 0.5 V. AES / EBU allows connection with a two-wire shielded symmetrical cable with transformer isolation through the RS-422 interface with a signal amplitude 3-10 V, connectors – three-pin XLR Cannon type. There are also options for optical transceivers: TosLink (plastic fiber) and AT&T Link (fiberglass).
