Data is expected to arrive at every component in a digital audio chain at exactly the moment dictated by a clocking signal. If this signal is absent or compromised in some way the result is a ‘clocking error’; either no audio, stuttering, clicking or a piercing degradation to the sound quality.
In the digital studio, every unit’s internal clock will be calibrated to the same sample rate, typically 44.1kHz. But no matter how carefully set up, there will always be a slight difference between units. Even if every unit were perfectly accurate there’s no guarantee that they would be exactly ‘in phase’; an error of less than a millisecond could cause the entire system to fall down.
Careful digital clocking solves this problem; a master device generates an accurate clock signal (typically in S/PDIF or AES3 format) and the slave units synchronise to it. The clocking device sets the ‘pace’ of the data, how much of it there should be and exactly when it should arrive; the slaves respond obediently.
Professional studios use expensive and highly accurate digital clocks to keep their units synchronised. In smaller studios with only one A-D converter in the set-up, it’s best to set this as your master clock and let everything else synchronise to that.