Kimmo, OptoFidelity’s expert at measuring video quality, tested the audio to video synchronization, or lip sync capability, of a Bluetooth speaker when streaming a YouTube video on a phone. The result was that the audio was ahead of the video by 120 ms, which interfered with the viewing experience and was clearly noticeable to the viewer.
For years, discussion forums have been buzzing over the lip sync problems of Bluetooth headphones, but according to a test by OptoFidelity, the same problems also plague wireless speakers that represent latest technology.
The test measured the playback of a YouTube video on an LG G3 phone connected to a Prego Bluetooth speaker. The test found that the audio was ahead of the video by 120 milliseconds, which is a difference in the audio to video synchronization that clearly interferes with the viewing and listening experience. In this respect, a Bluetooth speaker differs substantially from the phone’s own speaker or headphone jack. The phone’s own speaker played the audio with a lag of +40 milliseconds, and the headphone jack with lag of +60 milliseconds.
If the audio lags behind the video, the actor’s lips can be seen moving on the screen, but their voice will be heard afterwards. If the audio is ahead of the video, an actor’s voice will be heard before their lips are seen forming the lines and a sound effect will be heard before the event takes place on the screen, for example. There is no natural situation in which the audio would be ahead of the video, which is why this feels particularly disturbing to the viewers.
OptoFidelity has determined limits for the lip sync error that indicate how differences in synchronization affect the viewing experience
|Good||up to -15 ms ahead or +45 ms lag time|
|Moderate, the audio leading or lagging the video may interfere with the viewing experience||up to -45 ms ahead or +125 ms lag time|
|Poor, the lip sync error is clearly noticeable to the viewer||more than -45 ms ahead or +125 ms lag time|
More detailed measurements of the performance of a Bluetooth speaker could show whether the difference in playback can be attributed more to the phone or the speaker. To consumers, it does not always matter whether the difference is due to the phone or the speaker. It is clear, however, that the increasing use of wireless speakers in gaming and watching videos does not always provide a good user experience.
The test measurements were carried out using an OptoFidelity Video Multimeter measurement device, which makes it possible to measure the quality of a smartphone, tablet or any other multimedia device directly from a screen. One of the options of the measurement device is measuring the lip sync property of a device.
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