Familiar digital audio connection formats like AES3, S/PDIF, ADAT, and USB all incorporate an embedded clock signal which is extracted by the clock-recovery circuitry in the D-A, filtered to remove both intrinsic and cable-induced jitter, and then used to drive the D-A conversion process - and to be fair, that usually works pretty well! Instead, they almost always work as clock slaves, locking on to the sample rate of the incoming audio data stream. However, in the vast majority of cases, digital-to-analogue converters don’t contain a master clock circuit of their own. Of course, D-A manufacturers go to great lengths to try to achieve that, and so for that kind of application it might appear to make sense to have the system’s master clock built into the D-A converter. When recording, the most critical stage as far as clocking is concerned is undoubtedly the A-D, since this determines the digitisation quality, but in a mixing or mastering scenario it could be argued that the D-A converter demands the most stable and jitter-free clock. Hugh Robjohns replies: The stability and accuracy of the digital clock is most critical in the A-D and D-A conversion stages where signals are transformed between the digital and analogue domains. I have a very high quality D-A converter that boasts particularly low clock-jitter figures, so I thought it would be an ideal candidate to serve as a master clock - yet it doesn’t have a word-clock output socket! Am I missing something, or is there a good reason for that? Although some D-A converters, such as the Crane Song one pictured, have high-quality internal digital clocks, there are good reasons why these aren’t available via word-clock outputs.

Time clock world converter