Audio Delay Test
A free audio delay test: watch a flashing circle, listen for the click, and slide the offset until they happen together to read how late your sound arrives.
Loud. Turn it down if you wear headphones.
Your browser's reported latency shows here after you press Start.
Keyboard: Space starts and stops, ← → change 5 ms, with Shift 1 ms.
How to use the audio delay test
This audio delay test shows how far your sound lags behind your picture. Connect the speakers or headphones you want to check, for example Bluetooth earbuds, and press Start. Once a second the circle flashes white and a short click plays. Watch the circle and listen. If the click seems to come after the flash, drag the Sound offset slider to the right; if it comes before, drag it left. Use the −10, −1, +1 and +10 buttons to fine-tune, and Reset to 0 to start over.
When the flash and the click feel like one event, read the number: +150 ms means the page now sends the sound 150 milliseconds early to line up, so your sound path is about 150 ms slower than your picture. On a computer, Space starts and stops and the arrow keys move the offset by 5 ms, or 1 ms with Shift. The volume starts at 30%.
How the timing works
The flash and the click both come from the browser's audio clock. Each flash has a time on that clock, and the click is scheduled at that time minus your offset. The circle lights up when the browser says that moment is reaching your speakers, using the output position the browser reports. With the offset at 0, the flash and the click leave the browser together, so whatever offset you need is delay the browser does not know about: wireless links, the receiver, the TV or the screen itself.
Below the slider the page shows the base latency and output latency your browser reports, when it reports them. MDN describes output latency as an estimate of the time between the browser handing audio to the system and the first sample being processed by the output device. It is only what the browser reports, not a measurement.
Judged by eye and ear
This is a perception test, not a lab measurement. Your reading depends on how you judge the moment, and the screen may add a small delay of its own. Repeat it two or three times, approach the point from both sides, and take the middle of the range where it feels right. Broadcast engineers check lip sync the same way in principle: the EBU recommendation R37 describes a one-frame white flash and a 1 kHz tone burst as markers, and this test uses a 1 kHz click too.
How much delay is noticeable
Standards bodies have measured when people notice that sound and picture are out of step. Positive numbers mean the sound comes first; negative numbers mean the sound comes after the picture.
| Source | Sound before picture | Sound after picture |
|---|---|---|
| ITU-R BT.1359-1: detectable, on average | about 45 ms | about 125 ms |
| ITU-R BT.1359-1: acceptable, on average | about 90 ms | about 185 ms |
| EBU R37 (2007): end-to-end limit at the transmitter | 40 ms or less | 60 ms or less |
Both describe television sound and picture, but they give a useful scale: if this audio sync test shows your sound more than about 125 ms behind the picture, that is past the average detection threshold in the ITU table, and a Bluetooth audio delay of that size is worth fixing.
Fixing audio delay
If your TV, receiver, video player or phone has an audio delay or AV sync setting, enter the number from this lip sync test there, or use it as a starting point. Apple TV has Wireless Audio Sync, under Settings, Video and Audio, Calibration, which uses an iPhone to calibrate the audio so all speakers play in sync. A wired connection takes the wireless link out of the path, so you can test both ways and compare. To check that each speaker works first, use the speaker test, the headphone test or the surround sound test.
More for sound check: Mic Test · Sound Test · Speaker Test · Headphone Test · Left Right Test · Bass Test · Surround Sound Test · Speaker Cleaner · Tone Generator
Questions
How do I test Bluetooth audio delay?
Connect the Bluetooth headphones or speaker, run this test and slide the offset until the click matches the flash. Then run it again with wired headphones or the built-in speakers. The difference between the two numbers is roughly the extra delay of the Bluetooth path.
Is the result exact?
No. It depends on your eye and ear and on the screen's own delay, so repeat it a few times and take the middle. It tells you roughly how late your sound is, which is what you need for an AV sync setting.
What do the latency numbers from my browser mean?
Base latency and output latency are the browser's own estimates of its audio processing and output delay. The flash already allows for them. Delay added after the browser, by a wireless link or an external device, may not be included, which is why the slider is needed.
Why does my video have a lip sync problem only with headphones?
The wireless link can add delay that the player does not know about; Apple's Apple TV guide, for example, describes audio latency with wireless speakers. Measure the delay here, then use the AV sync or audio delay setting of your player or TV if it has one.