Word clock

<h2 id="comparison-to-timecode">Comparison to timecode</h2>
<p>Word clock should not be confused with <a href="/facts/Timecode/czFCXVC7">timecode</a>; word clock is used entirely to keep a perfectly timed and constant <a href="/facts/Bitrate/ppUNMmVd">bitrate</a> to avoid timing errors that can cause data transmission errors.  Timecode is <a href="/facts/Metadata/qt35z79C">metadata</a> <i>about</i> the media data being transmitted. Time code can be used as an initial phase reference for <a href="/facts/Jam_sync/JEuXJRtp">jam sync</a> using the word clock as the frequency reference.
</p>
<h2 id="over-coax-cable">Over coax cable</h2>
<p>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 <a href="/facts/Transistor%25E2%2580%2593transistor_logic/z4bvHotl">TTL</a> level, a 75ohm output impedance, 75ohm cables and a 75ohm terminating resistor at the end of a chain or cable.
</p><p>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 1's and 0's. 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 class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>A <i>chain</i> 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.
</p>
<h2 id="over-aes3">Over AES3</h2>
<p>The <a href="/facts/AES11/K3RnJYNb">AES11</a> standard defines a means for carrying a word clock over an <a href="/facts/AES3/Il4EdVYj">AES3</a> connection. In this context, the word clock is known as a <a href="/facts/Digital_Audio_Reference_Signal/K3RnJYNb">Digital Audio Reference Signal</a> (DARS).
</p><p>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.
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Phase-locked_loop/sgmca8aQ">Phase-locked loop</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"What is digital audio synchronization? How does it differ from time code synchronization?". Sweetwater. 27 April 2007. Retrieved 31 March 2021. <a href="https://www.sweetwater.com/sweetcare/articles/what-digital-audio-synchronization-differ-time-code-synchronization/#:~:text=%E2%80%9CSynchronization%E2%80%9D%20is%20an%20all%20encompassing,from%20the%20%E2%80%9Cmaster%E2%80%9D%20device." target="_blank">https://www.sweetwater.com/sweetcare/articles/what-digital-audio-synchronization-differ-time-code-synchronization/#:~:text=%E2%80%9CSynchronization%E2%80%9D%20is%20an%20all%20encompassing,from%20the%20%E2%80%9Cmaster%E2%80%9D%20device.</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Shelton, Tim (1 May 1989). "Synchronization of Digital Audio". Audio Engineering Society. Retrieved 31 March 2021. <a href="https://www.aes.org/e-lib/browse.cfm?elib=5460" target="_blank">https://www.aes.org/e-lib/browse.cfm?elib=5460</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Section 9.1.3 of Ardour manual <a href="http://ardour.org/files/manual/ch-synchronization.html" target="_blank">http://ardour.org/files/manual/ch-synchronization.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
</ol>

Word clock open-in-new

Word clock