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.