The term "clock" is broadly used in the field of digital audio to describe a signal used to both synchronize transmission of digital audio between devices and internally within each device for timing of all internal functions. These functions may include transmission between discrete IC's, memory, interfaces, and for conversion between analog and digital or digital and analog domains.
Digital audio as it exists today is based on the concept of quantization, where a continuously changing analog voltage waveform is encoded as a sequence of discrete voltage levels or “steps” at an extremely regular interval. The frequency at which each “sample” of the analog voltage is taken is referred to as the “sample frequency.” Internally; a digital audio device must have a “sample clock” that operates at the sample frequency in order to synchronize all internal operations. Most contemporary digital audio devices use serial data to transmit digital audio internally as well as externally (in the case of AES and S-PDIF interfaces); and this also requires a serial data clock or “bit clock.”
- Word Clock is a one cycle per sample period “square wave” signal.
- AES sync is similar to a bit clock in that there is one clock transition per bit embedded in the same signal as the digital audio data. The effective frequency of an AES sync signal is 64 times the sample frequency.