The USB-CEC Adapter has a maximum HDMI bandwidth of 4K@60Hz. If your display or content requires more bandwidth than this, you may see the TV turn off unexpectedly, the picture flicker, or the signal drop out when the adapter is connected between your PC and TV. This article explains what is affected and how to work around it.
What Is and Isn't Supported
| Signal / Format | Passes Through Adapter |
|---|---|
| 4K@30Hz | ✓ Yes |
| 4K@60Hz 4:2:0 | ✓ Yes |
| 4K@60Hz 4:4:4 or HDR | ✓ Generally reliable — use a High Speed HDMI cable (18Gbps rated) |
| 4K@120Hz | ✗ Not supported — causes flickering or signal loss |
| 8K | ✗ Not supported |
| Dolby Atmos (TrueHD / high-bitrate) | ✗ Unreliable — see related article |
| HDR10+ / Dolby Vision (high-bitrate) | ✗ May be unreliable at full bandwidth |
How to Tell If This Is Your Problem
You are likely affected if any of the following are true:
- Your TV or monitor supports 4K@120Hz or higher refresh rates
- The flickering or signal loss stops when you remove the adapter from the HDMI chain and connect your PC directly to the TV
- The issue only appeared after enabling a higher refresh rate or HDR mode in your display settings
- Your GPU is set to output 4K@120Hz or your TV is set to HDMI 2.1 Enhanced mode
If your setup runs at 4K@60Hz or below with standard HDR and the problem persists after removing the adapter, the cause is likely elsewhere. See: CEC Adapter — Not Being Detected.
Workaround: Connect the Adapter to a Spare HDMI Port
The most reliable fix is to move the adapter out of the main signal path. Your TV responds to CEC commands from any HDMI port — the adapter does not need to be on the same port as your video and audio.
Use your primary HDMI cable from your PC to your TV's HDMI 1 (or whichever port you normally use). This cable carries your full 4K@120Hz or HDR signal with no adapter in the way.
Use a short HDMI cable (under 2 metres) from the adapter's HDMI output to any other available HDMI input on your TV. Nothing needs to play through this port — it is used for CEC communication only.
The USB connection powers the adapter and carries CEC data. This does not change.
In CEC-Tray, open the Configuration tab and set the HDMI port number to match the port the adapter is plugged into. If using cec-client directly, add
-p X to your commands, where X is the port number (for example, -p 2 if the adapter is on HDMI 2).What If My TV Only Has One HDMI Port?
If your TV has only one HDMI input, the workaround above is not possible. In this situation the adapter cannot be used in-line with high-bandwidth content. This limitation cannot be overcome with the current hardware.
If CEC control is essential and you have an AVR or soundbar with spare HDMI inputs, connecting the adapter there may allow CEC commands to propagate through the AV chain — check your AVR's documentation for CEC passthrough support.
Related Articles
- CEC Adapter — Dolby Atmos and High-Bandwidth Audio
- Getting Started with the Pulse-Eight USB-CEC Adapter
- CEC Adapter — Not Being Detected
Contact Pulse-Eight support and let us know your TV model, GPU, and the resolution you are trying to run.
UK: 01202 413 610 | US: (858) 748-8250 | support@pulse-eight.com
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