Word Clock article
Common Word Clock Mistakes to Avoid
Most word clock problems trace back to a handful of common errors. This guide covers the mistakes most likely to cause clicks, dropouts or failed lock — and exactly how to fix them.
A word clock setup that almost works is more frustrating than one that clearly does not. The symptoms — intermittent clicks, devices that appear locked but drop out, or systems that work one day and fail the next — often trace back to a small number of recurring mistakes. These are the ones worth knowing before you start connecting cables.
Mistake 1: Having More Than One Clock Master
Every device in a digital audio system needs one timing master and only one. If two or more devices are set to "internal" clock simultaneously, each is generating its own independent timing signal. They will drift out of step with each other, producing clicks, pops or dropouts at irregular intervals.
The fix is simple: choose one device as master, set it to internal clock, and set every other device to the appropriate external source — word clock, ADAT, AES, S/PDIF, or whatever connection it receives timing through.
Mistake 2: Forgetting to Set the Slave's Clock Source
Connecting a word clock cable between two devices is not enough on its own. The receiving device must be told to use the incoming signal as its timing reference. Leaving the slave's clock source set to "internal" means it ignores the timing input entirely and continues running on its own oscillator, independent of the master.
Always check the clock source setting in the software control panel or hardware menu of every connected device. A slave with its clock source still set to internal is one of the most common reasons this system appears not to work.
Mistake 3: Incorrect Termination
A coaxial signal line behaves like a transmission line. Without correct termination at the far end of the run, the signal reflects back toward the source. This can cause unstable lock, clicks at unpredictable intervals, or a device that locks briefly and then loses it.
The last device in any BNC run needs 75-ohm termination. Many devices have a termination switch (sometimes labelled "75Ω" or "Term"). If a device has no internal termination, fit an external 75-ohm BNC terminator to the timing input or the unused end of the cable. Intermediate devices in a daisy chain generally should not be terminated — only the final one needs it.
Mistake 4: Using 50-Ohm Cable
Standard BNC distribution uses 75-ohm coaxial cable. Fifty-ohm coaxial cable is widely available — it is used for RF applications, antennas and certain networking purposes — and BNC connectors are common to both. It is easy to buy the wrong type.
Using 50-ohm cable creates an impedance mismatch that can cause reflections and unreliable lock, particularly over longer runs. The fix is to use the correct 75-ohm cable. If you are not sure what you have, check the cable's marking: 75-ohm coaxial will state "75 ohm" or "RG-59" (a common 75-ohm type); 50-ohm will state "50 ohm" or "RG-58."
Mistake 5: Daisy Chaining When a Star Layout Is Better
A daisy chain passes the signal from one device to the next in sequence. This can work, but each extra link in the chain adds a cable segment, a connector and a potential point of failure. It also makes termination more complex and troubleshooting harder.
A star layout — a separate cable from the master or clock generator directly to each slave — is cleaner, more reliable and easier to diagnose. If you are buying a generator, choosing one with enough independently buffered outputs for a star layout is worth the cost over a unit that forces you into a chain.
Mistake 6: Mismatched Sample Rates
A timing signal communicates timing, not sample rate. If one device is set to 44.1 kHz and another to 48 kHz, no amount of correct clock wiring will make them lock. The sample rate must be the same on every device in the system.
Check every device's sample rate setting — not just the master. It is common for a device's sample rate to be set correctly in one piece of software but persist at a different value in another. Confirming the setting in the hardware control panel as well as the DAW is good practice.
Mistake 7: Confusing Word Clock With Super Clock
Avid/Digidesign Pro Tools hardware uses a proprietary high-frequency clock format called Super Clock. This runs at a multiple of the sample rate (typically 256 times the sample rate) and is carried on a BNC connector, just like standard word clock. The two formats are not interchangeable.
Connecting a standard word clock output to a Super Clock input (or vice versa) will not produce a stable lock. If your system includes older Pro Tools hardware or a MOTU interface with Super Clock support, check the documentation carefully before routing any BNC connections to Pro Tools hardware.
Mistake 8: Assuming Any Instability Is a Clocking Problem
Clicks and dropouts in a digital audio system can have several causes beyond clocking: a USB buffer that is too small, driver conflicts, USB or Thunderbolt bandwidth issues, incorrect DAW buffer settings, or a ground loop in the analogue signal path. Assuming that synchronisation is always to blame and spending time rewiring a working clock setup is a common and time-consuming error.
If you are experiencing audio problems, confirm the clock setup is correct first, then check the DAW's buffer settings and the interface driver version before concluding the problem is in the clocking.
For a full overview of how it works, see the overview article. If you are setting up for the first time, the beginner's guide covers the basics step by step. For buying decisions, see the complete buyer's guide and the best word clocks for the money.
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