Identify which sounds are being compared
Wireless Audio Sync measures the latency of the television or receiver’s wired speakers so Apple TV can align wireless output. Apple describes it for a setup where HDMI audio and a wireless speaker can otherwise sound like an echo. That is a more specific situation than every report of dialogue being out of sync with lips.
Write down the two audible routes first. If you are hearing only one Bluetooth headset, or the programme itself has a timing error, do not assume this calibration addresses that case. Choose the tool that matches the actual output arrangement.
Measure the wired reference
On Apple TV 4K, open Settings, Video and Audio, Calibration, Wireless Audio Sync. Follow the iPhone prompts and hold the phone near the wired TV or receiver speakers as instructed. Apple plays calibration tones to measure that path.
Keep the room and output arrangement stable for the measurement. After it finishes, replay a familiar passage and listen to the combined outputs. Then check one route on its own. This comparison helps establish whether the original complaint was an echo between speakers rather than an issue present in each route independently.
Keep the result attached to its setup
A later change of receiver processing, television input or speaker arrangement can change what you are evaluating. Retain a note of the calibrated output route and repeat the documented process when that route materially changes.
The useful result is that the intended speakers play together acceptably. It is not evidence that every app, headset and television source has been tested. Describe the exact arrangement when asking for help.
Questions answered
Is Wireless Audio Sync a universal subtitle-delay control?
No. It concerns output synchronization; subtitle timing is a separate media or player question.
Where should the iPhone be during calibration?
Follow Apple’s prompts near the TV or receiver’s wired speakers, which provide the measured reference.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.