TABLE OF CONTENTS The standard two-channel interface was originally designed to accommodate digital audio signals with sampling rates between 32 and 48 kHz, with a margin of 12.5% to allow for varispeed operations. Since the interface carries audio data in real time, normally transferring two audio samples (channel 1 and channel 2) in the time of one sampling period, the data rate of the interface depends on the audio sampling rate. It is normally 64 times the sampling rate, since there are 64 bits in a frame (= two subframes). At a sampling rate of 48 kHz the data rate is 64 times 48 000, which is 3.072 Mb/s, whereas at 32 kHz it is only 2.048 Mb/s. If the source is varispeeded by a certain percentage then the data rate will change by the same percentage, and although it can usually be tracked by a receiver this presents problems in a system where all devices must be locked to a common, fixed sampling frequency reference (see Chapter 6), since the receiver may not change its sampling rate to follow a varispeeded source.
In recent years there has been a demand for interfaces capable of handling audio at increased sampling frequencies up to 192 kHz. For this reason a situation can arise in which one AES3 interface is used in a single-channel-double-sampling-frequency mode. Here the two subframes within a single AES frame carry successive samples of the same audio channel, making the audio sampling frequency...
