Checking Lip-Sync and Latency Before the Winter Schedule Starts
Priya Chandran sets out what to test in your audio chain during these weeks, before longer evening shows and seasonal programming put every microphone, mixer and playout path under load.
Why autumn is the right time to look at sync
Mid autumn is when many studios settle into their winter routine. Summer freelancers have gone, the regular crew is back, and the schedule fills with longer evening programmes, seasonal specials and live inserts. Any lip-sync fault that was tolerable in a quiet month becomes obvious when the same chain runs for hours every evening.
I have found that sync problems rarely arrive suddenly. They creep in through small changes: a replaced monitor with extra processing delay, a new playout encoder, a radio microphone swapped for a different model. Each change adds a few milliseconds, and nobody measures the total until a presenter's mouth and voice drift visibly apart.
A short audit now, while the diary still has gaps, costs far less in time and goodwill than chasing the fault in the middle of a live run in December.
Mapping the chain from microphone to playout
Start on paper. Draw every step the sound takes, from the capsule through the preamp, any digital conversion, the mixer, embedders, routers, encoders and finally the playout point. Do the same for the picture. Latency lives in the places people forget to list, such as frame synchronisers, up-converters and the wireless links between stage and gallery.
Write the quoted delay for each device beside it, then mark which ones are fixed and which change with settings. Sample rate conversion, buffer sizes and processing modes are the usual culprits. If a manufacturer figure is missing, note that it is unknown rather than guessing.
This drawing becomes the working document for everything that follows. When a fault appears later, you can see at a glance where a delay could have crept in, instead of arguing about whose equipment is to blame.
- List every device in the audio and video path
- Record quoted latency and the settings that alter it
- Mark wireless and network hops separately
- Keep one dated copy of the drawing with the gallery notes
Measuring rather than judging by eye
Watching a presenter and deciding that sync looks acceptable is unreliable, and tired eyes at the end of a long day are worse. Use a clapper test or a purpose-made sync pulse and flash signal, and compare picture and sound at the output with a scope or an editing timeline. A single measured number is worth more than a dozen opinions.
Test at more than one point. Measure at the mixer output, at the end of the playout chain and, where possible, on a receiving device such as a monitor fed from the stream. The difference between those readings tells you which section of the chain is responsible.
Repeat the test with the same source on a different day. If the reading moves, something in the chain is not stable, often a clock reference or a buffer that resizes itself under load.
Common faults to look for before winter
Clock reference problems are the most frequent cause of slow drift. If devices run on their own internal clocks rather than a shared reference, picture and sound slip apart gradually, often only after an hour or more. Check that every digital audio device is locked to the same source and that the lock indicator is steady.
Wireless microphones deserve attention as the colder months bring more outside broadcasts and radio frequency changes. Digital systems add a fixed delay that analogue ones did not, and mixing the two types on one stage produces odd offsets between performers.
Monitoring is another trap. A presenter hearing their own voice through a delayed foldback can speak awkwardly, and the crew may blame the programme feed for a fault that exists only in the earpiece. Check the talent path separately from the broadcast path.
- Unlocked or mixed clock sources
- Mixed analogue and digital radio microphones
- Buffer settings changed during software updates
- Delayed foldback mistaken for programme delay
Correcting offsets without creating new ones
Once you know the size and location of an offset, resist the urge to fix it at the nearest convenient point. Adding a delay to the audio at the final output corrects the programme, but it leaves the earlier stages out of step, which matters for any recording or secondary feed taken upstream.
Where possible, correct at the source of the problem: adjust a buffer, change a processing mode or lock a clock. Use an audio delay only for the remainder, and record exactly how much was added and where. Label it on the gallery desk so the next operator does not add the same correction again.
After every change, repeat the measurement. A correction that works at the mixer but shifts the stream by an extra frame is easy to miss, and it is the commonest way a tidy fix turns into a fresh complaint.
A short routine for the coming months
Sync is not a one-off job. I suggest a brief monthly check using the same test signal, the same measurement points and a simple log. It takes perhaps twenty minutes once the routine is set, and it gives you a record to compare against whenever a fault is reported.
Add a check after any equipment change, software update or new microphone type joins the rig. Keep the chain drawing up to date and make sure at least two people know how to run the test, so the knowledge does not sit with one engineer.
If a fault resists your own testing, an outside audit of the whole chain is often quicker than another week of guesswork, particularly when several suppliers' devices are involved.
- Monthly measurement with a fixed test signal
- Re-test after any change to the chain
- Two crew members trained on the procedure
Audio and picture drift is easiest to deal with before the busy winter schedule begins. Draw the chain, measure at several points, fix the cause where it arises and keep a simple log. These steps need no special budget, only a little time in the gallery during these quieter weeks, and they leave your crew with numbers they can rely on when the evening programmes run long.
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