Audio clocking in video applications

Abstract

A method of operating an electronic video device such as a DVD player, wherein video clock signals and audio clock signals are derived from a system clock signal using two phase-lock loops, and these video and audio clock signals are used to process encoded video data and encoded audio data, but digital-to-analog conversion of the audio data stream is controlled by the system clock signal rather than the audio clock signals. By using the system clock signal to control the audio digital-to-analog converter (DAC), the DAC avoids the poor performance issues that can arise from the jitter introduced into the audio clock signals by the PLL. The system clock signal may be divided by an integer to generate the sampling clock for the audio DAC. In the illustrative embodiment, the system clock signal has a rate which is not an integer multiple of the sample rate of the audio data stream. For example, the system clock rate might be 27 MHz while the sample rate of the audio data stream is 44.1 kHz. More generally, the system clock signal preferably has a rate of 108/N MHz, where N is an integer. A sample rate conversion unit in the audio DAC is used to convert the sample rate of the audio data stream to the rate of the system clock signal.