2. Signal modulation format
2.1 Audio signal
We have used S/PDIF (more commonly known as Sony
Philips Digital Interface) [23], a widely adopted standard
format used in digital audio transmission, especially in
home media entertainment devices. S/PDIF is a data link
layer protocol, which contains a set of physical layer
specifications for carrying digital audio signals between
devices and components over either optical or electrical
cables. S/PDIF is standardized in IEC 60958 as IEC
60958 type II (IEC 958 before 1998) and is essentially a
minor modification of the original AES/EBU standard
(used for digital audio signal transport) [17] for con-sumer electronics, employing small differences in the
protocol and requiring less expensive hardware. In S/
PDIF, the digital data stream is encoded using the
bi-phase mark code (BMC) also known as the differential
Manchester encoding, which is a kind of phase modu-lation in which clock and data signals are combined to
form a single two-level self-synchronizing bit stream
(see Figure 1), where the level change occurs at the
beginning of every bit period. It is a differential encoding
scheme, using the presence or absence of transitions to
indicate a logical value. Logics 1 and 0 are represented by
mid-bit level and no mid-bit level changes, respectively,
thus offering built-in synchronization capabilities.