Audio Latency & AV Sync Helper
Play a flash-and-click pattern to spot obvious audio delay and estimate how long the test tone takes to reach your microphone.
How this works
This tool attempts to play a tone and flash the screen at the same time. It uses your microphone to listen for the tone, then estimates the time between starting the test and the microphone hearing the sound.
Note: This is a practical troubleshooting helper, not a calibrated AV measurement. It is best for spotting obvious delay from Bluetooth headphones, TVs, soundbars, or unusual browser/audio routing.
Understanding audio-video sync (lip sync)
AV sync — also called lip sync — describes whether the audio you hear arrives at the same time as the video you see. When the two drift apart, it shows up first on close-up shots of people speaking: the mouth moves but the words land a fraction of a second early or late. Even small offsets are noticeable, and beyond about 100 milliseconds most viewers find them actively distracting.
Why does AV sync drift happen?
Modern video chains add latency at multiple points. A TV or display panel may do image processing — motion smoothing, scaling, HDR tone-mapping — before showing each frame. That processing takes time, and the amount varies by model and mode. Audio, meanwhile, takes its own path: through HDMI ARC, optical S/PDIF, Bluetooth, or analogue. Each path has a different delay characteristic.
- Wired audio (HDMI, optical, analogue) is usually lower latency than Bluetooth.
- Bluetooth headphones can add enough delay to make lip sync visibly wrong, depending on the codec and device.
- Soundbars and AV receivers may add processing delay, especially with virtual surround or enhancement modes enabled.
- TV picture modes such as motion smoothing or cinema processing can add delay compared with game mode.
How to fix lip sync issues
The simplest fix is usually in your TV, soundbar, AV receiver, or player settings if an "audio delay" or "lip sync" control is available. Use this test as a starting point, then fine-tune by eye. If the audio is leading the video (you hear the word before you see the lips move), add audio delay. If the audio is lagging, you usually can't delay the video — switch to a wired connection or enable a lower-latency Bluetooth codec.
Streaming apps (Netflix, Disney+, YouTube) generally handle their own AV sync internally and don't expose adjustment, but they sometimes interact badly with TV processing. If lip sync is wrong only on a streaming app, try toggling the TV's motion smoothing or "Cinema" mode off and see if it improves.