It describes the use of an encoding (or modulation) of information using Frequency modulation, also known as biphase mark code.

Manchester code (also variants Differential Manchester & Biphase mark code)

Biphase mark code (BMC)

The bits are encoded using the biphase mark code, also known as "FM": a zero bit has a single transition at the start of the bit period.

Instead, the data is sent using biphase mark code, which has either one or two transitions for every bit, allowing the original word clock to be extracted from the signal itself.

Biphase Mark Code (BMC) is used as the encoding method in AES3 and S/PDIF.

The line codes with this property include differential Manchester encoding, bipolar encoding, NRZI, biphase mark code, coded mark inversion, and MLT-3 encoding.

Differential Manchester encoding, also called biphase mark code (BMC) or FM1, is a line code in which data and clock signals are combined to form a single 2-level self-synchronizing data stream.

On top of the modulation, the IEEE 1902.1 recommend two encoding methods: BMC, Bi-phase Marc Coding Biphase mark code, known as a Manchester Encoding technique.

No attempt was made to use a carrier able to support both rates; instead, AES/EBU allows the data to be run at any rate, and recovers the clock rate by encoding the data using biphase mark code (BMC).