Abstract: Circuitry for transferring multiple digital data streams, e.g. digital audio data, over a single communications link such as a single wire. A pulse-length-modulator is responsive to a plurality of data streams to generate a series of data pulses with a single data pulse having a rising and falling edge in each of a plurality of transfer periods defined by a first clock signal. The timing of the rising and falling edge of each data pulse is dependent on a combination of the then current data samples from the plurality of data streams. The duration and position of the data pulse in the transfer window in effect defines a data symbol encoding the data. An interface receives the stream of data pulses, and data extraction circuitry samples the data pulse to determine which of the possible data symbols the pulse represents and determines a data value for at least one received data stream.