Quick Answer: One source and two displays means one shared EDID. The splitter reads both sinks and sends the timing the least capable one accepts, so a 4K60 panel beside a 1080p panel drops both to 1080p unless the box has a scaler. HDCP is the second gate: both displays must complete the handshake or neither shows a picture. For 4K60 at 4:4:4 you need 18 Gbit/s end to end, so keep passive cable runs under 15 ft (4.5 m) on both outputs.
The splitter does not copy a picture, it copies a timing. Whatever the source agrees to send is what every output receives, and the agreement is reached before the first frame.
How EDID arbitration works
Each display stores an EDID block describing its supported timings. A splitter presents one merged block to the source, and most units take the intersection: the highest timing both displays accept. Two 1080p60 panels give 1080p60. A 4K60 panel and a 1080p panel give 1080p60, because 4K is not in the second display’s list. A unit with a scaler can instead keep 4K on output one and downscale to 1080p on output two, which is the only way to give each screen its own resolution.
When the two displays differ
Mixed estates are the normal case: a new 4K panel next to a five-year-old projector. Either accept a common 1080p timing, which is free, or buy a scaler, which costs more and adds 1 to 2 frames of latency. A splitter with a fixed 1080p output and a 4K input will usually blank the 4K display, because the source is told the sink cannot accept the timing. hdmi splitter switch sets out where a switch is the better part when the displays are never used at the same time.
Bandwidth and cable rules
HDMI 1.4 carries 10.2 Gbit/s, which is enough for 4K30 at 4:4:4 or 1080p120. HDMI 2.0 carries 18 Gbit/s for 4K60 at 4:4:4, and 2.1 carries 48 Gbit/s. A splitter rated for 4K60 must pass 18 Gbit/s through both outputs, so a passive 18 Gbit/s-rated cable is required on each leg; a cable that works directly from source to display can still fail through a splitter because the splitter adds a connector pair and its own driver. The bandwidth comparison in hdmi 1.4 vs 2.0 covers the timing to chroma combinations that fit each tier.
Splitter classes compared
Outputs are HDMI unless stated, and cable lengths assume certified passive leads.
| Class | Outputs | Max resolution | HDCP | Scaling |
|---|
| Passive splitter | 2 | 1080p60 | 1.4 only | no |
| Powered, 4K30 | 2 | 3840 x 2160 at 30 Hz | 2.2 | no |
| Powered, 4K60 | 2 | 3840 x 2160 at 60 Hz | 2.2 | no |
| Powered with scaler | 2 | 4K60 in, 1080p out | 2.2 | yes, per output |
| Powered, 4 outputs | 4 | 1080p60 | 2.2 | no |
Power, audio and the handshake
Almost every 4K splitter needs its own 5 V supply, and a bus-powered unit that claims 4K60 will usually fall back to 1080p when both outputs are loaded.
Audio follows the weakest sink
Audio follows the same negotiation: if one display reports stereo only, the merged EDID can force stereo on both, so a surround system fed from the second output may receive two channels. Set the source to bitstream only after confirming that both sinks accept the format.
Practical scenarios
- Situation: Conference room with a 4K display and a 1080p projector used together. Fit a 4K60 splitter with a scaler on output two, so the room keeps 4K on the main screen and 1080p on the projector.
- Situation: Retail window with two identical 1080p panels 40 ft (12 m) away. Use a powered splitter and active optical leads beyond 25 ft (7.6 m), because a passive 18 Gbit/s lead will not hold at that length.
- Situation: Bar with four screens showing one game. A four-output 1080p60 splitter is cheaper and more stable than cascading two two-output units, which doubles the handshake time.
- Situation: Existing wall plate with a short lead to the display. Join the splitter output to the plate lead with an hdmi coupler only if the total run stays under 15 ft (4.5 m); otherwise replace the plate lead with a single cable.
Failure symptoms and their causes
A picture that appears for two seconds and then goes black is a handshake loop, usually caused by one sink losing power or by a cable with no hot plug detect on pin 19. A picture with pink or green sparkle is a bandwidth fault on one leg, so swap the cables between outputs to identify which. Resolution stuck at 1080p on a 4K source means the merged EDID is being honoured, not that the splitter is faulty.
FAQ
Does a splitter reduce picture quality?
No, the signal is digital and either arrives intact or fails visibly. What a cheap unit does reduce is the available bandwidth, which shows up as a lower resolution or dropped frames rather than a softer picture. Sparkle and blackouts are the symptoms to look for.
Can I split a 4K60 source to two 4K60 displays?
Yes, with a powered unit rated at 18 Gbit/s and two certified passive cables under 15 ft (4.5 m). Both displays must accept the same timing, and both must support HDCP 2.2 if the content requires it. Longer runs need active optical cable.
Why do both screens go blank when one is switched off?
Switching a display off removes its EDID from the merge, so the source renegotiates and the remaining display briefly loses sync. Units with per-output EDID memory or a fixed internal EDID hold the timing steady. That feature is worth checking before purchase.
