Frequently Asked Questions

DVI and HDMI transmit video signals in a digital format as opposed to the traditional analog VGA/SVGA format. Digital transmission technology results in a superior quality image over analog transmission technology due to analog's sensitivity to the phase changes of cables. This is also the reason DVI and HDMI are better than component video.

The only drawback of digital transmission technology is that the data being transferred can only maintain full fidelity for about 5 meters with DVI and about 15 meters for HDMI. Cable runs can be increased with the use of fiber optic technologies, amplifiers, and repeaters, however, their incredible expense makes the idea commonly unreasonable.

DVI vs HDMI · How far a cable can run · Active vs passive adapters

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DVI makes use of Transition-Minimized Differential Signaling (TMDS) wherein eight bits of video data are converted to a 10-bit transition-minimized, DC-balanced value. This value is then serialized and sent to the receiver where the data is de-serialized and converted back to eight bits.

The three TMDS signals needed for RGB make up one TMDS link. A DVI connector can carry up to two TMDS links providing for better resolutions and timing requirements. Single TMDS link DVI cables can support resolutions and timings that use a video clock rate of about 25-165 MHz.

The following resolutions and timings are supported by a single link DVI cable:

• SXGA resolution (1280 x 1024) with 85-Hz refresh rate
• UXGA resolution (1600 x 1200) with 60-Hz refresh rate
• SDTV resolutions of 480i, 480p, 576i and 576p
• HDTV resolutions of 720p and 1080i

Video clock rates of 165-330 MHz on the other hand, are supported only by dual TMDS link DVI cables. With dual link DVI cables, however, each TMDS link operates at only one-half the frequency of single link DVI. So the clock and bandwidth is shared by these two links.

Single link vs dual link DVI · What your port and cable can drive

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Along with the introduction of DVI technology came the need to prevent the digital video data from being pirated, or copied without authorization. In order to address this issue High-bandwidth Digital Content Protection (HDCP) was derived. HDCP, developed by the Intel Corporation, implements a key encryption encoded into the DVI signal which, without the proper HDCP decoding mechanism, produces either extremely low resolutions or static. To avoid this, both source and display devices must have DVI connections that support software key HDCP decoding.

HDCP, also used by the new HDMI technology, was strongly endorsed by the entertainment industry, for obvious reasons. What makes this technique of key encryption possible is its renewability. The Digital Content Protection LLC, an organization responsible for licensing of the HDCP technology, monitors the secret keys used to encrypt the data. If at any time they believe a set of secret keys has been compromised by an unauthorized source, those keys are placed on a revocation list and new keys are provided to devices authorized by license.

HDCP also uses a method of authentication to ensure that the receiving device is licensed to receive HDCP encrypted data. This authentication process repeats itself every few seconds in order to be certain that an illegal device has not been connected after the initial authentication. If and when this authentication fails, the source device will immediately end all encrypted transmissions.

Modern 4K/UHD content uses newer revisions, HDCP 2.2 and 2.3, which are not backward compatible with HDCP 1.x. Every device in the chain — including any adapters, splitters, or AV receivers — must support the newer version, or the protected content will not display.

Fixing an HDCP black screen · HDMI technology

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Consumer Electronics Control (CEC) is an optional protocol used in HDMI systems that allows HDMI devices to pass control functions along to all devices within the system. CEC was designed to operate at low speeds with minimal processing and memory overhead.

The following is a set of all the features offered with CEC:

• One Touch Play - A device may be played and become the active source by the press of a single button.
• System Standby - Enables devices to be set on standby by the press of a single button.
• Preset Transfer - A device's presets can be auto-configured to match those of the TV.
• One Touch Record - Allows recordings to be made by the press of a single button.
• Timer Programming - Any device can program a timer recording on a recording device.
• System Information - Allows devices to auto-configure their language and country settings.
• Deck Control - Allows a device to control and interrogate a playback device.
• Tuner Control - Allows a device to control the tuner of another device.
• Vendor Specific Commands - Allows vendor-defined commands to be used.
• OSD Display - Allows a device to display text using the on-screen display of the TV.
• Device Menu Control - Allows a device to control the menu of another device.
• Routing Control - Enables control of CEC Switches for streaming of a new source device.
• Remote Control Pass Through - Allows Remote Control commands to be passed along to other devices within the system.
• Device OSD Name Transfer - Devices may request the preferred OSD name of other devices within the system.

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Audio Return Channel (ARC) is an HDMI feature that lets a TV send audio back to a soundbar or AV receiver over the same HDMI cable, removing the need for a separate optical or audio cable.

Enhanced Audio Return Channel (eARC), introduced with HDMI 2.1, greatly increases the audio bandwidth so it can carry high-bitrate and object-based formats such as Dolby Atmos and DTS:X.

For either to work, the TV, the audio device, and the cable must all support ARC (or eARC), and the feature must be enabled on the TV's HDMI ARC/eARC port.

HDMI technology · HDMI 2.0 vs 2.1

HDMI vs DisplayPort · Which HDMI cable you need

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An analog signal degrades smoothly, so a long VGA run simply looks progressively softer. A digital link either reconstructs each pixel exactly or it does not, so it holds a perfect picture right up to the point where the signal is too weak to decode, then fails abruptly: sparkles, dropouts, flicker, or a black screen.

That is why a marginal digital cable can look perfect one moment and unusable the next, and why a longer passive cable is rarely the answer. The fix is the right type of cable for the distance.

How far each cable can run · Flicker and dropout fixes

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Bandwidth is how much data per second the link has to carry, in gigabits per second. It is resolution × refresh rate × colour depth × chroma multiplied together, so 4K at 120 Hz needs roughly four times the data of 4K at 30 Hz.

Every interface version has a ceiling, and so does every cable rating. The link runs at whichever of the two is lower — which is why a new graphics card with an old cable still will not reach its advertised mode.

What your port and cable can drive · Calculate a mode's bandwidth

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Because the connector and the standard are separate things. An HDMI port from 2012 and one from 2024 are physically identical, but implement different versions of the specification — roughly 8 versus 42 Gbit/s of usable bandwidth. Nothing on the outside of the port tells you which you have.

The same trap applies to USB-C, where the connector says nothing about whether the port carries video at all. Check the device specification, not the shape of the socket.

Look up a device's ports · HDMI 2.0 vs 2.1

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No. There is no such thing as an “HDR cable” or a “VRR cable.” Both are features of the source and display, negotiated between them, and both simply need enough bandwidth on the link.

HDR does use 10-bit colour rather than 8-bit, raising the data rate by about 25%, so a cable that was marginal at 8-bit can start failing once HDR is switched on. Buy for the bandwidth the mode needs and the features follow.

HDR explained · Variable refresh rate · What cable labels really mean

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A cable joins two compatible connectors directly.

A passive adapter re-routes a signal that is already compatible — digital DVI to HDMI, for instance, since both use TMDS. It changes the plug shape, not the signal. These are inexpensive and frequently work in only one direction.

An active converter contains powered electronics that genuinely translate one signal into another: HDMI to DisplayPort, or anything crossing between digital and analog. They cost more and may need external power.

Active vs passive adapters · Find the right one for your devices

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HDMI, DisplayPort, and USB-C in DisplayPort Alt Mode all carry audio alongside video. DVI and VGA carry none at all, in any variant.

That is why a DVI-to-HDMI adapter gives a picture but silence, and why no better adapter will fix it: the audio was never present on the DVI side. Run a separate audio connection from the source instead.

DVI vs HDMI · ARC and eARC

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Multi-Stream Transport is a DisplayPort feature that sends several independent display streams down a single cable, so monitors can be chained one to the next rather than each needing its own port on the source.

It needs DisplayPort on the source and a DisplayPort output on the first monitor. All chained displays share the one link's bandwidth, so two 4K screens at 60 Hz demand far more headroom than two 1080p ones. HDMI has no equivalent feature.

Setting up dual monitors · Check the bandwidth you have

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