Knowledge Base

The HDMI Licensing Knowledge Base is a library of current information about the HDMI standard. Select an appropriate category from the pull down below, or, you may use your own search terms to obtain results.

If your question involves a specific product, please contact the manufacturer directly. The HDMI Knowledge Base does not contain information about specific products.

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Installation Tips

Q. Can I use HDMI to connect one from to another using wall plates?

You can connect from one room to another using wall plate connections. However, the quality of the wall plate can affect the transmission. Be sure to select an HDMI-compliant wall plate that fits your specific installation requirements.

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Q. What is the difference between Active HDMI and Passive HDMI?

There is no active or passive HDMI in the test specification. These terms apply to cables. Active cables have built-in electronics to enable long cable runs, and typically these cables require a power supply. These cables use active electronics to help push the signal farther than typical passive cables.

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Q. Do I need v1.3 HDMI to hear the new Dolby TrueHD and DTS Master HD audio content on HD-DVD or Blu-ray players?

No. The Dolby TrueHD, Dolby Digital Plus, and DTS-HD Master Audio can be decoded by the playback device into multi-channel Pulse Code Modulation (PCM) digital audio streams, which is an audio format standard that can be sent over any version of HDMI. In fact, all versions of HDMI can support up to 8 channels of PCM audio at 192kHz, 24 bits per sample.

To do this, consumers should ensure that their playback device (such as HD-DVD or Blu-ray player) is capable of decoding these new lossless Dolby & DTS audio formats into the PCM format on the HDMI output, and that the audio device (such as an A/V receiver) is capable of receiving multi-channel PCM audio over the HDMI inputs. Consult your user manual/product specification sheet to determine whether your device supports such PCM capabilities (we believe that nearly all HD-DVD and Blu-ray players will, but users should confirm this). Devices that support HDMI v1.3 and higher may also offer the option to transport the high definition audio formats as a compressed, encoded stream over HDMI so that the decoding function can be performed by the A/V receiver (whereas the above transport method has the playback device performing the decoding).

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Q. What is the difference in quality between listening to Dolby TrueHD/DTS-HD over HDMI, SPDIF (i.e. coax or optical), or analog from the player to the A/V receiver?

HDMI provides the highest quality as it enables the full, lossless audio data of Dolby TrueHD to be transferred digitally to the AV receiver, and enables the A/V receiver to apply its full digital audio processing capabilities (such as bass management, or sound field processing effects) to further enhance the audio quality. S/PDIF does not have the ability to support the data rates required by Dolby TrueHD, and thus will not support it. Analog will be lower quality than HDMI due to two reasons: 1) the nature of analog transmission is lossy and will degrade while transported over the cables, 2) many A/V receivers will not apply any digital audio processing to the analog inputs, and in such cases analog signals will be sent directly to the amplifier without the benefit of such processing.

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Q. What is the difference between decoding Dolby TrueHD/DTS-HD in the player (i.e. sending over HDMI as decoded PCM) vs. decoding in the A/V receiver (i.e. sending over HDMI as encoded Dolby TrueHD/DTS-HD bitstream)?

There is no inherent difference in quality between Dolby TrueHD/DTS-HD being sent over HDMI as decoded PCM vs. encoded bit stream. All Dolby TrueHD/DTS-HD decoders (whether in the player or the A/V receiver) must be certified to meet stringent quality requirements. However, consumers should make sure that their receivers support the number of incoming PCM channels delivered by their source device (e.g. DVD).

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Q. Some cable TV set-top boxes with HDMI outputs don’t deliver a picture to displays with HDMI inputs. What is the problem, and is there a solution?

In some cases, the set-top box software does not activate or support the HDMI port. In other cases, cable TV set-top boxes don’t work correctly when used in conjunction with an A/V receiver (but will typically function correctly when connected directly to a TV or monitor). Investigation of some of these devices reveals that this is caused by an error in the way these set-top box devices implement HDCP. Specifically, some of those boxes do not support "HDCP repeaters" (devices that pass along the signal to another device) such as an A/V receiver or switch. We believe that this may be a problem in the initial versions of these products, and in some cases there is new firmware available that fixes this issue in HDMI (newer versions may already have this fix). We have been actively working with manufacturers to resolve these problems. We suggest that users contact their cable operator and request the new software to address these issues. As noted above, cable operators are increasingly downloading the available firmware upgrades required to fix this error.

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Q. If an HDMI accessory device (i.e. switch box, cable booster) does not have a dedicated power supply, is it still compliant and will it work?

An HDMI device that has active electronics should have a provision for external power in order to be compliant (e.g. a receptacle to allow the use of a standard power adapter, sometimes called a power “brick”). Here we are drawing a distinction between “active” devices that actually have some powered electronics, and “passive” devices, such as some switches (more on those later).

Some active devices, such as actively powered HDMI cables or in-line signal extender boxes, will by default attempt to power their electronics by taking power from the 5V line (+5V power) available on the HDMI connector. The HDMI specification requires all source devices to provide at least 55mA (milliamps) on the 5V line for the purpose of reading the EDID of a display. While 55mA is not enough current to operate most HDMI accessory devices (which typically require about 100 to 150mA), most source devices on the market today provide significantly more current on the 5V line than the HDMI specification requires. As a result, the vast majority of accessory devices can operate when interfaced with a source device that provides more than the required current (i.e. over 100-150mA) on the 5V line. However, manufacturers should provide a provision for their powered HDMI accessory devices to obtain external power, and consumers are encouraged to look for this external power provision when purchasing such products.

Looking to the future, not all HDMI devices may provide this much power over the 5V line. For example, as HDMI expands into more and more portable applications (cameras, camcorders, laptops, etc.), power consumption is often much more of an issue, and such devices may not power the 5V line with the > 100mA required by such “active” devices. Again, consumers should consider ensuring that their active HDMI accessory device purchases have a provision for external power for this reason.

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Q. Can any passive devices that use no active electronics (such as a mechanical switch box) be compliant?

Any device which performs processing, amplification, or switching of the HDMI signal should use actively powered electronics to be compliant and perform reliably. As mentioned in the above question, the vast majority of devices can utilize power that is supplied on the 5V line (+5V power) of the HDMI connector to function properly, although we recommend that such devices give the users an optional provision to use an external power adapter. Completely passive, non-powered devices may work in some short-cable length applications, but use them at your own risk, as they may not operate reliably. Even if a passive device works in one configuration, a change in equipment or cabling may introduce failures in subsequent configurations.

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Q. Does HDMI accommodate long cable lengths?

Yes. HDMI technology has been designed to use standard copper cable construction at long lengths. In order to allow cable manufacturers to improve their products through the use of new technologies, HDMI specifies the required performance of a cable but does not specify a maximum cable length. We have seen cables pass "Standard Cable" HDMI compliance testing at lengths of up to a maximum of 10 meters without the use of a repeater. It is not only the cable that factors into how long a cable can successfully carry an HDMI signal, the receiver chip inside the TV or projector also plays a major factor. Receiver chips that include a feature called "cable equalization" are able to compensate for weaker signals thereby extending the potential length of any cable that is used with that device.

With any long run of an HDMI cable, quality manufactured cables can play a significant role in successfully running HDMI over such longer distances.

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Q. How do I run HDMI cables longer than 10 meters?

There are many HDMI Adopters working on HDMI solutions that extend a cable’s effective distance from the typical 10 meter range to much longer lengths. These companies manufacture a variety of solutions that include active cables (active electronics built into cables that boost and extend the cable’s signal), repeaters, amplifiers as well as CAT5/6 and fiber solutions.

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Q. My HDMI cable sometimes falls out of the HDMI connector. Is anything being done to address this problem?

The combination of vertically-oriented connectors and heavy, thick-gauge cables appears to have the potential of causing the connector to fall out. In some cases, it is due to the usage of a cable with a non-compliant, large connector over-molding that prevents proper connector engagement. The HDMI Founders are actively investigating a locking connector option that would be backward compatible with existing Standard (Type A) connectors.

We have seen a few connectors that are out of spec (e.g., not the right size, too much over-molding, etc.), which led to compatibility issues and, in some cases, connector damage. However, in December 2005, we implemented a connector certification program to help ensure that all Adopters use compliant connectors.

Several manufacturers are now selling “port savers” – short, flexible sections of HDMI cable that easily bend at a right angle for applications where the HDMI cable requires a 90 degree bend directly out of the connector. Without these “port savers,” heavier cables can put undue pressure on the connector and the connectors can dislodge.

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Q. Can HDMI cables contribute to devices not working properly together?

The vast majority of image quality or interoperability issues with HDMI devices are related to the software (firmware) used for device communication and content protection, and have nothing to do with the HDMI cable. In particular, these issues are often caused by the software related to HDCP handshaking, or from devices improperly handling the device capability information read through HDMI (e.g. the device has an incorrect EDID, or an inability to properly read an EDID). It is fairly uncommon for the cable to be the cause of HDMI compatibility problems. In fact, the robustness of the HDMI specification has been verified by the fact that we have not found a compliant HDMI cable that is the root cause of HDMI playback issues with compliant devices.

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Q. How can I tell if a cable is an HDMI certified cable?

All HDMI products are required to be certified by the manufacturer as part of the HDMI Compliance Test Specification. However, there may be instances where cables bearing the HDMI logo are available but have not been properly tested. HDMI Licensing Administrator, Inc. actively investigates these instances to ensure that the HDMI trademark is properly used in the market. We recommend that consumers buy their cables from a reputable source and a company that is trusted.

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Q. What is the difference between a “Standard” HDMI cable and a “High-Speed” HDMI cable?

Recently, HDMI Licensing Administrator, Inc. announced that cables would be tested as Standard or High-Speed cables.

  • Standard (or “category 1”) HDMI cables have been tested to perform at speeds of 75Mhz or up to 2.25Gbps, which is the equivalent of a 720p/1080i signal.
  • High Speed (or “category 2”) HDMI cables have been tested to perform at speeds of 340Mhz or up to 10.2Gbps, which is the highest bandwidth currently available over an HDMI cable and can successfully handle 1080p signals including those at increased color depths and/or increased refresh rates from the Source. High-Speed cables are also able to accommodate higher resolution displays, such as WQXGA cinema monitors (resolution of 2560 x 1600).
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Q. Will my Standard cable work in High Speed applications?

Although a Standard HDMI cable may not have been tested to support the higher bandwidth requirements of cables rated to support high speeds, existing cables, especially ones of shorter lengths (i.e., less than 2 meters), will generally perform adequately in higher speed situations. The quality of the HDMI receiver chip (in the TV, for example) has a large effect on the ability to cleanly recover and display the HDMI signal. A significant majority, perhaps all, of the HDMI TVs and projectors that support 1080p on the HDMI inputs are designed with quality receiver chips that may cleanly recover the 1080p HDMI signal using a Standard-rated HDMI cable. These receiver chips use technology called “cable equalization” in order to counter the signal reduction (attenuation) caused by a cable. We have seen successful demonstrations of 1080p signal runs on a >50 ft. cable, and a 720p signal run on a >75 ft. cable. However, the only way to guarantee that your cable will perform at higher speeds is to purchase a cable that has been tested at the higher speeds and labeled as “High-Speed.”

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