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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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Q. Do I need a separate audio cable if my if my HDMI output is a physical DVI (DVI to HDMI adapter) port is not a true HDMI port?
Digital Visual Interface (DVI) is a video interface standard designed to maximize the visual quality of digital display devices such as flat panel LCD computer displays and digital projectors. Because DVI is a video-only standard, a graphics card with DVI port, even one with a DVI-HDMI adapter sends uncompressed digital video data to a display but does not send audio.Return to top

Q. What is the advantage of using HDMI over existing audio interfaces such as analog RCA connectors and digital SPDIF (coax and optical connectors)?

Quality: HDMI maintains the audio in its pure digital form all the way to the amplifier. Analog audio connections are more prone to losses depending on the cabling and other electronics of the audio rendering device.  Compared to SPDIF connections, HDMI has significantly more bandwidth, allowing it to support the latest lossless audio formats such as Dolby TrueHD and DTS-HS Master Audio. These formats can not be supported over SPDIF connections due to their very high data rate requirements that exceed the capabilities of SPDIF. Please also see section on HDMI 1.3 for further details on Dolby TrueHD and DTS-HD Master Audio formats.

Ease of Use: HDMI combines video and multi-channel audio into a single cable, eliminating the cost, complexity, and confusion of multiple cables currently used in A/V systems. This is particularly beneficial when equipment is being upgraded or added.

Intelligence: HDMI supports two-way communication between the audio source (such as a DVD player) and the audio rendering device (such as an A/V receiver), enabling new functionality such as automatic configuration and one-touch play. By using HDMI, devices automatically deliver the most effective format (e.g Dolby Digital vs. 2 channel PCM) for the A/V receiver that it is connected to - eliminating the need for the consumer to scroll through all the audio format options to guess what is best and properly supported.

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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. Why is Lip Sync important?

In a DTV, typically the video processing takes more time than the audio. As a result, lip sync can become an issue where it is noticeable to the viewer, creating an effect similar to that of a badly-dubbed movie. HDMI 1.3 provides a method whereby the audio processing times in devices can be automatically adjusted to remove lip sync errors.

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Q. Does HDMI support Dolby 5.1 audio and high-resolution audio formats?

Yes. From the start, HDMI was defined to carry 8-channels, of 192kHz, 24-bit uncompressed audio, which exceeds all current consumer media formats. In addition, HDMI can carry any flavor of compressed audio format such as Dolby or DTS. (Such compressed formats are the only multi-channel or high-resolution audio formats that can be carried across the older S/PDIF or AES/EBU interfaces.) Additionally, most existing HDMI sources can output any compressed stream, and the newer sources can output uncompressed 6-channel, 96kHz audio from a DVD-Audio disk. There are A/V receivers on the market that can accept and process the 6- or 8-channel audio from HDMI.

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Q. Does HDMI support Dolby Digital, DTS, and high-resolution audio formats?

Yes. From the start, HDMI was defined to carry 8-channels of 192kHz, 24-bit uncompressed audio, which exceeds all current consumer media formats. In addition, HDMI can carry any currently available flavor of compressed audio format such as Dolby (including Dolby Digital EX 7.1, Dolby Digital Plus 7.1, Dolby TrueHD) or DTS (including DTS-ES 6.1 and DTS-HD Master Audio). Such compressed formats are the only multi-channel or high-resolution audio formats that can be carried across the older S/PDIF or AES/EBU interfaces. HDMI 1.3 adds additional support for new lossless digital surround audio formats Dolby TrueHD and DTS-HD Master Audio. Additionally, most existing HDMI sources can output any compressed stream, and the newer sources can output uncompressed 6-channel, 96kHz audio from a DVD-Audio disk. There are A/V receivers on the market that can accept and process the 6- or 8-channel audio over HDMI.

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Q. Does HDMI support SACD?

HDMI has supported One Bit Audio format, such as SuperAudio CD's DSD (Direct Stream Digital), since version 1.2 (released in August, 2005). Customers interested in this feature should make sure that their device supports SACD.

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Q. As more and more devices converge, is HDMI an interface that can accommodate convergence between the PC and CE?

Absolutely. HDMI was developed using the same technology as DVI (Digital Visual Interface), the digital connection standard for the PC environment. So, HDMI is fully compatible with all DVI-enabled PCs (since HDMI offers both audio and video over one cable, and DVI carried only video, DVI-HDMI connectivity requires a separate audio cable).

HDMI enables PCs to deliver premium media content including high definition movies and multi-channel audio formats. HDMI is the only interface enabling connections to both HDTVs and digital PC monitors implementing the DVI and HDMI standards – fully compatible with the hundreds of millions of DVI displays already in the market.

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Q. What is the DDC?

DDC stands for Display Data Channel. In a video system, the vast majority of information flow occurs from a source to a sink where the video and/or audio travels. DDC provides a back channel from the sink to the source to indicate events like hot-plug. In addition, it allows the sink to communicate its display output capabilities back to the originating source device. Without this feature, devices like graphics cards or DVD players would have to guess at what video/audio formats a display would like to see. The DDC specification is currently at rev DDC-CI and is available from VESA (www.vesa.org).

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Q. What is EDID?

EDID stands for Extended Display Information Data. This is the data contained (usually in a small EEPROM) on each DVI display or HDMI sink. There may be as many as one EDID per DVI or HDMI input.

The source device checks the display’s DVI or HDMI port for the presence of an EDID prom and uses the information inside to optimize the output video and/or audio format. The EDID data structure can be for either VESA PC devices or for CEA-861B E-EDID (Enhanced EDID) devices. All sink devices compliant to the DVI or HDMI specification must implement EDID.

An EDID PROM is used only in sink devices. An EDID PROM sits on the DDC channel and uses a 2-wire I2C bus (part of the DDC specification from www.vesa.org) to communicate from the sink to the source. The EDID PROM contains information about the sink that it resides in. Its job is to communicate the preferred (or supported) video and audio formats and resolutions to the originating source. As an example, when a DVD player is powered on, it reads the EDID from an attached HDTV. The HDTV will have in its EDID contents that it is a Samsung 17” LCD panel that supports native resolution of 1280x1024 pixels, but can also support 480p, 720p and 1080i video modes. The EDID may also say that the TV is an HDMI device and has 2-speakers. The DVD player would compare this information with what it can put out of its HDMI port, then set itself to send 1080i with 2-channel stereo to the HDTV.

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Q. What is the difference between EDID and E-EDID?

EDID was formed as a standard to help PC monitors report their capabilities. E-EDID is an extension of the EDID specification used traditionally by consumer electronic devices to illustrate more advanced features.

For example, PC monitors generally do not support audio, so a traditional EDID structure would not account for this, whereas an E-EDID would.

The requirements for a consumer electronics device’s E-EDID are available in the CEA- 861B specification (www.ce.org).

The requirements for a PC device EDID are available from VESA (www.vesa.org).

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