Wordclock

Word Clock is a basic clock in the digital audio equipment which is necessary to allow the transmission of audio data streams from digital audio equipment. Using word clock must be synchronized processing the digital data of all devices involved. The word clock is just the period of a sample at a given sampling rate, regardless of the dynamic range used.

Each digital audio device has an internal clock generator which provides him in stand-alone mode the base clock available with which it processes the audio data. In the composite of two or more digital audio devices, a device must accept this clock to wordclock pretend (master) and all other devices (slaves). That's where every digital device of its internal switch to an externally supplied clock. It is not enough, the internal clock generator easy to adjust for each device in the network at the same clock frequency. The clock frequencies then run unsynchronized alongside each other and drift apart. This asynchrony of the digital data leads to clearly audible pop and click noise to a complete loss of signal.

Standardized clock or sampling frequencies (see sampling rate) are 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz and 192 kHz. For most digital audio formats can the wordclock from the data stream of the received audio data can be derived ( eg, S / PDIF, AES / EBU, ADAT, MADI ), but not TDIF. If the word clock signal separately transferred from the digital audio signal, so this is usually done through coaxial 75 -ohm cables with BNC connectors. For this, the connected devices require dedicated BNC Word Clock connections, which is the case only in professional equipment.

From the word clock master clock signal can be either by " daisy chain " like a chain to the next and managed by this on to the next device, etc. ( on the last device in the chain, the line must then be necessarily terminated with a 75 ohm terminating resistor), or the clock signal is star-shaped distributed directly to all other devices from the master. Since sum for serial transmission of the clock signal at every other device on the chain small clock delays, the clock speed of one device to inaccurate and can cause signal dropouts. Therefore, the star-shaped word clock distribution should be preferred, in which the clock master to be synchronization signal directly to synchronize feeds each device.

In principle, any digital audio device that has a digital output, function as the word clock master. Consumer devices, in particular CD player, which of course have no audio input, it must always be the word clock master. Some professional CD players, however, are equipped for external clocking with word clock inputs.

In the professional field independent word clock generators are often used. These are devices that generate only word clock signals and output and have the star-shaped distribution over multiple connections.

Listening tests have shown that jitter; influenced tiny inaccuracies in the wordclock source, the audio quality already heard negative, before it comes to clicking sounds or even dropouts. Therefore, some engineers swear by especially high-quality ( and expensive ) word clock generators that produce extremely precise clock signals, such as a rubidium oscillator.

If a device without external clocking option (eg CD player ) can be connected with a word clock master, the master is published on the relevant input have a sample rate converter, which converts the clock speed of the CD player to the actual system clock.