Audio Sync

How to Check and Fix Lip Sync Drift Before a Live Show

A step-by-step method for finding audio delay in a studio chain, measuring it against picture, and setting compensation so presenters and playback stay aligned for the whole programme.

Daniel Okafor

28 October 20265 min read

How to Check and Fix Lip Sync Drift Before a Live Show

Why sound and picture drift apart in the first place

Most sync problems are not mysterious. Video passes through converters, frame synchronisers, vision mixers and multiviewers, and each of those stages holds a frame or two while it works. Audio often takes a shorter route, so it arrives early. The gap is small on any single device and only becomes visible once several stages stack up between the camera and the output.

The result is a presenter whose lips close a moment before you hear the word. Viewers notice it at around two frames of error, and they rarely complain precisely; they simply feel the programme is slightly off. Before changing any setting, draw the full path for one camera and one microphone, from source to transmission, and mark every box that touches either signal.

This drawing is the most useful document in the whole exercise. It tells you where delay is added, where it can be corrected, and which devices you can safely leave alone.

List every device in the video path, including converters and monitors you feed
List every device in the audio path, including embedders and de-embedders
Note which units state a fixed latency and which change with the signal format

Measure first: a simple clap test and a proper line-up

Start with a measurement you can repeat. Put someone in front of a camera with a microphone, ask them to clap sharply on a slate or with a hand clap, and record the programme output on a device that shows waveform and frames together. Step through to the frame where the hands meet, then compare it with the frame where the spike appears on the audio track.

Write the offset down in frames and in milliseconds, and note the frame rate, because the same delay reads differently at 25 and 50 frames per second. Repeat the test on every camera you use, since a camera with a longer lens chain or an extra converter will show its own figure.

If you can get a purpose-made sync generator that flashes and beeps together, use it for the line-up, and keep the clap as a quick daily check.

Record at least ten claps and average them to avoid a single bad reading
Test each camera separately, not only the main one
Log results with the date, source and frame rate

Applying delay compensation where it belongs

Once you know the gap, delay the audio rather than trying to advance the picture. Most mixing consoles and audio routers let you add delay on an output or an input in milliseconds, and that is the cleanest place to correct it. Set the value to match your measured offset, run the clap test again, and confirm the spike and the picture meet on the same frame.

Avoid scattering small corrections across several devices. Two engineers each adding a little delay in different places is how a chain ends up with a fault nobody can explain a month later. Choose one point, document it, and keep every other stage at zero.

If you work with embedded audio, check whether the embedder or the downstream de-embedder is already compensating. Some units correct automatically, and adding your own value on top will push the sound late.

Apply delay at a single named point in the chain
Keep other devices at zero unless the manual requires otherwise
Write the final value on the rack or in the show file

Mixing set-ups that make drift easier to spot

A tidy mix helps you hear sync trouble early. Keep presenter microphones on their own faders and groups, route them through the same processing, and avoid sending a delayed signal to talkback or foldback, where performers will hear a lag and start to speak oddly. For monitoring, give the floor a foldback feed taken before the compensation delay.

Remote contributors need separate thought. A guest on a return feed will always arrive later than the studio, and the fix is a mix-minus with its own delay so the guest hears themselves without echo. Label each bus clearly so a stand-in operator can see which paths carry delay and which do not.

Check the mix with the studio monitors turned down and headphones on a quiet moment before doors open. Small timing faults stand out when the room is silent.

Group presenter microphones together and keep processing identical
Feed performers a non-delayed foldback
Use a labelled mix-minus for remote guests

Re-checking through the season and when kit changes

Sync is not set once and forgotten. Whenever you swap a camera, add a converter, change the output format or update firmware, the delay can change without any sign on the front panel. In these autumn weeks, when schedules fill and rigs are reconfigured for new series, build a short sync check into the pre-show routine so it takes two minutes rather than twenty.

Keep a simple log with the measured offset, the compensation value and who checked it. When something drifts, you can compare against known good readings instead of starting again. If a fault appears only on one camera or one output, the log narrows the search quickly.

Teach every operator the clap test. The person who notices a problem first is usually the one on the desk, not the one in the equipment room.

Re-test after any change to kit, format or firmware
Keep a dated log of offsets and settings
Make the clap test part of the standard pre-show checklist

Good lip sync comes from a measured path, one place for delay and a habit of checking again. Draw the chain, run the clap test on each camera, apply compensation at a single documented point and log the result. With those steps in place, drift becomes a quick fix before the show rather than a complaint after it, and your presenters stay comfortably in time with their own voices.