science

Word clock

Word clock is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Word clock rather than just read about it. In short: In digital audio electronics, a word clock or wordclock (sometimes sample clock, which can have a broader meaning) is a clock signal used to synchronise other devices, such as digital audio tape machines and compact disc players, which interconnect via digital audio signals. Word clock is so named because it clocks each audio sample.

Key takeaways

Word clock belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Word clock to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Word clock from memory before moving on to harder problems.

Reference excerpt

In digital audio electronics, a word clock or wordclock (sometimes sample clock, which can have a broader meaning) is a clock signal used to synchronise other devices, such as digital audio tape machines and compact disc players, which interconnect via digital audio signals. Word clock is so named because it clocks each audio sample. Samples are represented in data words. S/PDIF, AES/EBU, MADI, ADAT, and TDIF are some of the formats that use a word clock. Various audio over Ethernet systems use communication protocols to distribute word clock. The device that generates the word clock is the clock source for all the other audio devices. The signal is used for synchronizing digital audio signals between devices, such as CD players, audio I/O cards, etc. It allows all the components in the signal path to process the data and remain synchronized with each other.

Comparison to timecode Word clock should not be confused with timecode; word clock is used entirely to keep a perfectly timed and constant bitrate to avoid timing errors that can cause data transmission errors. Timecode is metadata about the media data being transmitted. Time code can be used as an initial phase reference for jam sync using the word clock as the frequency reference.

Over coax cable Professional digital audio equipment may have a word clock input or output to synchronize timing between multiple devices. Although the electrical characteristics of the word clock signal have not been completely standardized, some characteristics should always apply. Items that should remain consistent are TTL level, a 75ohm output impedance, 75-ohm cables and a 75-ohm terminating resistor at the end of a chain or cable. Proper termination of the word clock signal with a 75ohm resistor is important. It prevents the clock signal from reflecting back into the cable and causing false detection of extra 1s and 0s. Some digital equipment includes a switchable terminator, some include a hardwired terminator and others have no terminator at all. An unfortunate aspect is that some equipment manuals do not indicate whether a hardwired terminator is included. A chain connection from the source through the receivers may increase jitter. Using clock-distributing devices for parallel transmission is a better method. The length and quality of coaxial cables are important.

Over AES3 The AES11 standard defines a means for carrying a word clock over an AES3 connection. In this context, the word clock is known as a Digital Audio Reference Signal (DARS). In Annex B, the AES11 standard also describes common practice in transmitting and receiving a plain word clock signal. This is not an attempt to standardize it; the annex is informative only.

Worked examples

Example 1 — a first encounter with Word clock

Start with the simplest possible case. Write down what Word clock claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Word clock before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Word clock ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Word clock

In research: Word clock appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Word clock in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Word clock is common in secondary-school and first-year university syllabi. It links to neighbouring topics Digital audio, so understanding it makes those chapters shorter.
In everyday life: Look for Word clock outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Word clock in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Word clock means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Word clock out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Word clock in simple terms?

Why does Word clock matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Word clock?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Word clock.