Abstract: A computer audio interface unit (110) comprises a serial computer interface (e.g. USB) (204) providing a connector (112) for connection to an external, computer-based source (100) of digital audio data samples. A digital audio output connector (130) provides a digital audio output signal to external audio reproduction apparatus (106, 108). A word clock output connector (134) provides a word clock signal to external audio reproduction apparatus, in parallel with said digital audio output signal. An encoder (202/308) receives digital audio data via said USB interface and outputs said digital audio output signal. Clocking circuitry (202/300, 312) is responsive to a timing reference signal (200) independent of said external source (100), and generates said word clock signal for output to the external reproduction apparatus.