Banding is a bit depth problem: 8-bit gives 256 steps per colour channel, 10-bit gives 1,024, and a slow sunset gradient across a 65-inch panel is where 256 stops being enough. Chroma subsampling — the 4:4:4 and 4:2:0 numbers people argue about — costs you colour detail at edges, not gradient smoothness.
Which matters here, because it rules out most of the advice you'll find.
What the Apple TV can and can't do
The Apple TV 4K's HDMI port is labelled 2.1, but it uses the older TMDS signalling rather than FRL, so the link is capped at 18Gbps and the box cannot output 4:4:4 at all. Its HDMI 2.1 support covers eARC and QMS, not the bandwidth.
Two consequences:
Moving it to your TV's 48Gbps port changes nothing. The source is the bottleneck. This is the most common piece of advice on this topic and it doesn't work.
It isn't dropping to 8-bit either. HDR10 and Dolby Vision require 10-bit, and when you select a 4K HDR format tvOS keeps the bit depth and reduces chroma to 4:2:2 or 4:2:0 instead. So the banding you're looking at is not the box running out of bandwidth for bit depth — it never had the option to trade the other way.
That leaves three real causes.
Cause 1: forced Dolby Vision
This is the big one, and it's a setting.
If Format is set to 4K Dolby Vision, the Apple TV converts everything into Dolby Vision — including SDR and HDR10 material that was never graded for it. Your TV then applies Dolby Vision tone-mapping to content that doesn't want it, and the result is banded, dim, sometimes oddly tinted.
Fix it in two places:
- Settings > Video and Audio > Match Content > Match Dynamic Range = On
- Set the format to 4K SDR — on current tvOS that is usually Settings > Video and Audio > Format
With those set, each title plays in the format it was actually mastered in and the tone-mapping stops being applied to things that were never HDR. The Match Frame Rate and Dolby Vision settings guide goes through both toggles properly.
If banding disappears after this change, you're done. For most people it does.
Cause 2: the stream
Streaming services encode at a fraction of a disc's bitrate, and dark slow gradients are the hardest thing to compress — night skies, smoke, underwater scenes, a studio backdrop behind an interview. The encoder discards exactly the fine gradation you're staring at.
The tell is that it happens on one title and not others. If a particular film bands and everything else is clean, that's the master or the encode, and nothing on your end recovers data that was never sent.
Cause 3: the TV's processing
Turn off noise reduction and smoothing on that input. Both are filtering processes that can introduce their own contouring in flat areas while trying to clean up compression artefacts.
Some sets also have a Smooth Gradation option (Sony's name for it) that dithers the remaining steps. It's masking rather than fixing, but it works and it's free.
While you're in there, make sure the input's enhanced mode is on — LG HDMI Deep Color, Samsung Input Signal Plus, Sony Enhanced format, TCL HDMI Enhanced Mode, Hisense HDMI Signal Format set to Enhanced Format. That's what lets the port carry 10-bit HDR at all. It's per-input, so enabling it on HDMI 2 does nothing for the box on HDMI 3.
Two tests that save an evening
Look at the Apple TV's own screensaver. The aerials play back locally rather than streaming, so if those look clean and your content doesn't, the problem is upstream of your setup — the encode, not the box.
Play the same scene in the TV's built-in app. If it bands there too, with the Apple TV out of the chain entirely, it's the panel or the stream. That's thirty seconds and it eliminates half the possibilities.
What about the cable?
Largely a red herring for banding specifically.
A failing HDMI cable announces itself: sparkles, white speckles, flicker, or the picture dropping out entirely. It does not quietly reduce your bit depth — the link either carries the format the two ends negotiated over EDID or it visibly falls apart. So if your picture is stable and merely banded, the cable is not your problem.
Swap one in to rule it out by all means. Just don't expect it to be the answer.
See also
FAQ
Why does HDR band when SDR doesn't? HDR uses the PQ curve to cover a far larger luminance range, and it exposes quantisation in dark and near-black areas where SDR simply never goes. HDR is actually the higher bit depth of the two — 10-bit against SDR's 8 — it's the range that makes the steps visible.
Should I move the Apple TV to an HDMI 2.1 port? It won't help banding. The Apple TV's link is capped at 18Gbps regardless of what it's plugged into.
Can the Apple TV output 4:4:4? No. It uses TMDS signalling rather than FRL, so 4:4:4 isn't available at 4K. This is a hardware limit, not a setting.
One show bands and nothing else does. That's the encode. Dark slow gradients are what streaming compression handles worst.
Does a better cable fix banding? Almost never. Bad cables produce sparkles and dropouts, not banding. Rule it out, then move on.