Measure how long sound takes to go out and come back on this device. A short click is scheduled on the audio output, the microphone is recorded, and the recording is cross-correlated with the click to find where it arrived. Repeating that a few times gives a median and a spread, which together say more than one number.
Running it
Keep the room quiet, turn the speakers to a moderate level, and start. The microphone opens with the browser’s voice processing off: echo cancellation exists to remove the speakers from the microphone, which is the very thing being measured. The clicks play about a second and a half apart.
Reading the result
The large number is the median of the trials that heard the click. Below it, the min and max show the spread, and the trial list shows each measurement with the correlation that backs it. A trial under the correlation floor is marked not heard and left out.
The round trip includes the air. Sound travels about 34 cm per millisecond, so a microphone a metre from the speaker adds about 3 ms. For the electronics alone, bring the microphone close to the speaker.
Browser output latency
The browser declares a latency for its own output path, shown for comparison. It is the delay before a scheduled sound reaches the hardware; the round trip adds the input side and the acoustics. A large gap between the two on a short acoustic path points at the input chain.
Where it stops
This is the path the browser uses, not necessarily the one a recording application with its own driver uses. It is also one device: measuring an interface means running it with that interface selected as both input and output in the system settings.