Display Port 2.1 UHBR20 vs HDMI 2.1 Bandwidth and DSC Artifacts: Edge Cases, Failure Modes, and Root-Cause Debugging

[Jayden Ward]

I’ve been pushing 4K 240Hz through UHBR20 (80 Gbps lanes) on my RTX 5090, and I’m seeing intermittent tearing at the exact moment my frame rate dips below the display’s compressed bandwidth ceiling. My question: at what point does DSC compression actually introduce visible artifacts in fast-moving competitive titles like Valorant or CS2, versus just dropping frames cleanly? I’m reading that DSC is “visually lossless,” but I’ve noticed color banding in dark gradients after enabling it, and I’m not sure if that’s the DSC encoder or downstream chroma subsampling kicking in.

For anyone running 4:4:4 uncompressed at these refresh rates—what’s your real-world stable bottleneck, and where does the signal actually break down? Specifically, does HDMI 2.1’s 48 Gbps ceiling with FRTF compression behave differently than DP 2.1’s UHBR20 when you hit those edge cases where the encoder can’t sustain lossless compression? Anyone here found a specific resolution/refresh combo where DSC artifacts become unavoidable even on a certified Ultra High Speed cable?

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