Logitech C920x A/V Sync & Latency Test

Logitech C920x A/V Sync Test: Measure Webcam Audio Offset for OBS

C920x delivers 1080p/30fps over USB-A and Logitech lists the C920 family as a USB 2.0 UVC webcam with 78° diagonal field of view and autofocus.¹ Connect the cable, open this page in Chrome or Edge, click "Enable Camera & Mic", and the browser requests camera and microphone tracks through getUserMedia before it can read either stream.²

The C920x video path usually carries more processing than the microphone path because the camera sends video frames while the browser receives audio samples as a separate MediaStream track. The measured offset can be positive or negative depending on the USB controller, operating system, and browser state, so use your five-clap result rather than a generic published figure. When the result says Audio Delay, enter the positive value in OBS Studio's microphone Sync Offset field to delay the audio until it matches the video frame.

Specifications¹

Connection and browser setup

Connect the C920x to a USB port directly on your computer rather than through a hub. USB hubs and shared host controllers can change bandwidth availability, and Microsoft describes USB bandwidth as a shared controller resource that varies by system and device topology.³ Chrome and Edge both support the getUserMedia API the tool requires; grant camera and microphone permissions when prompted. After granting access, select your microphone from the audio input dropdown if multiple devices appear.

Hot-plugging is supported. Disconnect and reconnect the cable at any time and the browser device selector refreshes automatically without reloading the page. If the camera does not appear in the video input list, confirm the browser has camera permission in your operating system settings, not just in the browser's site permission dialogue.

Camera and microphone permission checklist

Before the test session, trace the C920x cable to confirm it runs directly into a rear motherboard port rather than into a USB extension cable or hub. Extension cables and hubs add extra device topology between the camera and the host controller, which can widen the spread across your five clap readings. A tighter spread gives you more confidence in each individual reading, so move the C920x to a port on a separate controller if the readings jump around.

Common A/V sync issues with this model

USB bandwidth contention is the most common source of elevated offset on the C920x. When other high-bandwidth USB devices share the same USB host controller, the camera's video stream and the microphone stream compete with the rest of the device tree for controller time. Microsoft notes that USB bandwidth competition comes from both hardware and software, so moving the C920x to a different USB port can test whether those ports sit behind a separate controller.³

Keep room lighting stable if your five readings spread apart, because changing brightness can make the luminance spike harder for the detector to timestamp cleanly. Inconsistent lighting forces the camera to adjust exposure between claps, which changes the baseline luminance level and can shift the apparent peak of the transient by one frame in either direction.

USB host controller position and offset variance

Device Manager shows which host controller serves each USB port on your machine. Open Device Manager, expand Universal Serial Bus controllers, and look for multiple USB host controller entries; most modern desktop boards list two to four. Right-clicking a host controller entry and selecting Properties then the Devices tab shows which ports share that controller. Moving the C920x from a port on a busy controller to a port on a less-loaded controller reduces contention, tightening the spread across your five measurements without changing your average offset.

What the test covers

The tool clocks a visible luminance transient in the video frame against a simultaneous amplitude transient in the audio stream. It reads canvas pixel data with getImageData to find the video spike, then uses Web Audio time-domain data to find the matching audio spike.⁴⁵ Inside the browser, both timestamps use the same performance.now() clock, so the measurement is a direct comparison rather than an estimate.⁶ Five clap pairs average out individual frame jitter and timing outliers.

Beyond the raw offset number, the result screen shows the direction label: Audio Delay (positive value), Audio Leads (negative value), or In Sync (within ±5 ms). Building on this, copy the OBS Audio Offset value and paste it directly into OBS Studio under Edit > Advanced Audio Properties for your microphone source. OBS forum guidance identifies that dialog as the place to enter Sync Offset in milliseconds, where 1 second equals 1000 ms.⁷

Using OBS Audio Offset correctly

Copying the OBS Audio Offset value immediately after the result displays avoids re-running the test when you open OBS. The result screen does not persist after page navigation. Paste the value directly into the Sync Offset field in OBS Advanced Audio Properties while the conditions that produced the measurement still apply: the same USB devices connected, the same background processes running. An offset value captured and applied within the same session reflects the same USB bus state that produced the measurement.

Apply the value while the page stays open. The result screen does not reload, so the offset you copied reflects the USB bus state that produced it. Treat a reading inside ±5 ms as In Sync, but still apply it if viewers report drift, because small residual gaps surface only during fast motion. Close background apps and retest your C920x after a USB port swap, since that shift can change the average offset enough to matter.