What is digital audio synchronization? How does it differ from time code synchronization?

The following article comes from our friends at Aardvark:

“Synchronization” is an all encompassing term used in digital audio which refers to the various processes of keeping all “slave” digital devices locked together following the timing data from the “master” device. It is an extremely vital, although somewhat complicated process which is crucial to the operations of today’s complex digital studios. In digital audio, there are two types of synchronization, generally referred to as “digital audio synchronization” and “time code synchronization”. Both types of synchronization should be thought of as working independently of one another, but do often work hand-in-hand to provide the proper interaction between digital devices in a studio.
Digital audio synchronization can be considered synonymous with sample rate. It is a timing reference which keeps sample accurate sync between digital devices keeping them running together, locked at the same speed. Every digital device needs to reference a clock source (either internal or external) in order to trigger its internal operations. An A/D converter, for example, uses the clock rate as a timing reference to know when to take a digital sample of the analog wave form.
Digital audio devices are equipped with a crystal, an electronic component made from a piece of quartz crystal, which it uses to generate its internal timing reference. These devices usually have the choice of clocking to their own internal crystal, clocking to an incoming digital audio signal (which carries its own clock), or by clocking to another digital audio device or master clock source. The last two examples have their limitations and drawbacks.
* Clocking to an audio signal, such as an AES/EBU or S/PDIF input carrying audio, can work in most situations. It is not, however, the best way to send and receive clock data. Data-dependent jitter caused by the audio data being in the same data stream as the clock data, makes this method less effective than a dedicated word clock or AES/EBU black signal.

* Slaving to another device can work fine in a simple setup between two digital devices. However, daisy-chaining multiple digital devices together as a means of synchronization is not recommended. Daisy-chaining will certainly add jitter to the signal resulting in loss of audio fidelity and can lead to audible “clicks and pops” in the audio. Not good.

The best way, to clock a digital studio is to use a stand alone, ultra low-jitter master clock generator, such as how the AardSync II connects a discrete clock output to each digital device.

The AardSync II features Aardvark’s proprietary AardLock™ Technology, and has become widely recognized as the industry standard master word clock sync generator of choice, throughout the world. AardLock™ Technology is a sophisticated digital technology which ensures exceptional jitter reduction, resulting in a pure and precise audio clock signal. The AardSync II will instantly improve the performance of A/D converters and add resounding depth and clarity to any digital mix. For its achievements in engineering the AardSync II, Aardvark received a TEC award nomination from Mix Magazine in 1997.
The most common digital audio clock formats include word clock, AES/EBU, S/PDIF, video black, and Digidesign Superclock (256). The AardSync II has the ability to output clock in all common formats, as well as lock its clock to an incoming video blackburst signal.
Time code synchronization is used to provide positional reference, allowing multiple digital devices to locate to a specific point in time. Examples of time code sync would include controlling of a digital or analog tape deck multitrack recorder from a remote controller, locking several multitrack recorders together to create more tracks, synchronizing a MIDI sequencer to a DAW, or syncing a video recorder to an audio recorder while doing post production. Common time code formats include LTC, VITC, and MIDI Time Code (MTC). For the purposes of this FAQ we will focus primarily on digital audio synchronization, with a some references to time code as needed.

Knowledge Base