A Short Guide to
HDMI Cables and HDMI Connectors
...the de-facto standard in HDTV connectivity
First we had DVI. Soon HDMI followed with its different versions and a full range of HDMI cables, HDMI connectors, adaptors, splitters, switches, etc.
Yet, despite the increasing presence of HDMI, there is still a lot of consumer confusion about this 'do-it-all' AV interconnect especially when it comes to the different versions of HDMI and the supported features.
This needs no longer be the case! This two-part practical guide to HDMI explains all there is the need to know about HDMI. In this first part, we discuss the main features, the different HDMI versions, and the differences between HDMI and DVI-D. In the second part, we give details as to the different HDMI cable types and HDMI connectors supported by this AV interconnect.
MediaBridge High Speed HDMI Cable
with Ethernet and Audio Return
The HDMI standard — short for High Definition Multimedia Interface — was first released in December 2002. Labeled as HDMI ver. 1.0, it was the first industry supported interface that carried uncompressed all-digital audio and video over the same interconnect.
This was followed by HDMI ver. 1.1 in May 2004, and ver. 1.2 in August 2005; the latter was then updated to ver. 1.2a in December of the same year.
But the version list did not stop there:
Version 1.3 followed in June 2006; an update followed to version 1.3 in November of the same year; this was the ver. 1.3a. This was then updated again to Ver. 1.3b in March 2007 and ver. 1.3c in August 2008. In May 2009, a newer HDMI version was released labeled as ver. 1.4; the latter requires a different HDMI cable to support the added Ethernet channel defined in the new standard. This was followed by HDMI ver. 1.4a in March 2010 and by ver. 1.4b in October 2011.
And now we have HDMI 2.0; HDMI 2.0 paves the way to high-end 4K TVs at up to 60 fps. It was announced by the HDMI Forum during IFA2013 - more than a year later than expected but... finally, it is here! Do not expect HDMI 2.0 products to be available anytime soon; the specs are now available, yet it will take time till chip makers design their chips and even more so, for manufactures to start implementing the new HDMI chips within their products. We expect HDMI 2.0 hardware to be available sometime late during 2014.
The first HDMI-enabled consumer products started to appear on stores shelves in late 2003, just a few months following the release of the first version of HDMI. Since then, HDMI saw an exponential rise in the rate of annual growth of HDMI-enabled products, and soon became the 'de-facto' standard for HDTV connectivity. It is estimated that today, there are more a couple of hundred million HDMI-enabled devices worldwide!
The HDMI standard was founded by leading consumer electronics manufactures—Hitachi, Panasonic, Philips, Sony, Toshiba, Thomson and Silicone Image.
Because HDMI is fully compliant with HDCP (High-Bandwidth Digital Content Protection) copyright protection, the HDMI standard is also fully supported by major content providers including motion picture producers Fox, Warner Bros, and Disney, as well as by system operators like DirecTV and EchoStar.
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The principle idea behind HDMI is the use of a single AV interconnect instead of several cables when connecting audio and video sources from say a set-top-box or Blu-ray player to an AV receiver, HDTV, etc., over a single HDMI cable.
The use of a single HDMI cable that replaces the maze of AV cables often found behind home entertainment centers is the primary advantage brought about by this AV standard. This is not the case with DVI; DVI supports digital video only, meaning that a separate audio cable (TosLINK or SPDIF) is required to transport digital audio when video is carried over DVI.
But there are other additional advantageous as well
HDMI transfers uncompressed digital audio and video leading to the best digital quality possible since there is no degradation of the signal through compression/decompression processes.
It is fully backward compatible with DVI; all that is required is a DVI to HDMI cable adaptor. This opens HDMI to a wide range of DVI-equipped products from a variety of manufacturers.
HDMI supports two-way communication between the video source and the display device, thus enabling new functionality such as automatic configuration e.g. in the case of remote controls of devices connected over HDMI.
HDMI technology has been designed to accommodate longer copper cables at lengths up to 15 meters (50 feet) without the use of HDMI amplifiers or repeaters; this is typically three times as much as the maximum cable runs supported by DVI interconnects.
Furthermore, HDMI cable lengths less than 15 ft can be relatively inexpensive; note however that there are some difference here between HDMI cables manufactured to Category 1 specifications and those manufactured to Category 2 specs. This category difference in HDMI cables surfaced with the introduction of HDMI 1.3 in 2006; the HDMI standard defines two cable categories:
Category 1-certified cables - tested at up to 74.5 MHz (720p60 and 1080i60
Category 2-certified cables - tested at 340 MHz (1080p60 and 2160p30)
Later in October 2008, Category-1 HDMI cables started to be marketed as 'Standard' while Category-2 HDMI cables as 'High Speed'.
Supported Cable Length
We have stated that the HDMI standard supports longer cable lengths than DVI, but…
Actual performance constraints vis-à-vis cable length are very much similar to DVI in view that HDMI uses the same encoding protocol over the same twisted copper pair.
As indicated in our DVI Cable Guide, the use of twisted copper pair to carry high bit-rate digital data without error correction can lead to severe problems with signal degradation over distance. It is for this reason that the HDMI specifications standard does not specify a maximum cable length, but rather defines the expected performance parameters—such as far-end crosstalk, attenuation, and differential impedance—that need to be met by an HDMI interconnect.
The HDMI specs support standard NTSC and PAL, enhanced, and high-definition video formats, plus 8-channels of 192kHz 24-bit uncompressed digital audio on a single HDMI cable. However, the actual supported image resolutions, audio standards, and features are dependent on the respective HDMI standard.
At this point, it is important to realize that some of the features specified by the various HDMI standards are not mandatory. Features such as support for 1080p 60Hz, Deep Color—which increase the precision of the supported brightness and color information, xvYCC for an extended color space that is 1.8 times that of standard sRGB, and Super Audio CD DSD support, are optional and therefore manufacturers may opt not to implement these features.
This means that a product having a specific HDMI version does not necessarily support all features listed for that HDMI version.
HDMI Version Comparison
HDMI Version 1 specifies the basic audio/video HDMI interconnect. It supports a maximum TMDS bandwidth of 4.95 Gbit/s—with a maximum allotted video bandwidth of 3.96 Gbit/s (165 MHz) supporting up to 1080p/60 Hz video 24 bit color depth, and 36.86 Mbit/s maximum audio bandwidth for up to 8 channels of 192 kHz 24-bit audio resolution.
In addition, HDMI version 1.0 also supports Blu Ray disc video and audio at full resolution and CEC - short for Consumers Electronics Control. The latter is often branded differently by different manufactures and enables the user to control HDMI connected devices via a single control unit.
However, while CEC was included with HDMI version 1, it wasn't before the release of Version 1.2a that all relevant CEC features, command sets, and CEC compliance tests were eventually specified to the full.
HDMI Version 1.1 added support for DVD Audio while HDMI Version 1.2 added support for One Bit Audio (used on Super Audio CDs) for up to 8 channels, this apart from additional features related to supported color space by PC sources. And as stated in the previous paragraph, Version 1.2a specified for the first time the complete set of specs for the Consumer Electronic Control (CEC) support.
HDMI Version 1.3 brought about significant enhancements to the original HDMI specifications—with the most important being increase in the single-link bandwidth to 340 MHz or 10.2 Gbit/s data stream.
It also supports Deep Color with 30-bit 2560x1600p75, 36-bit 2560x1600p60, and 48-bit 1920x1200p60 xvYCC color space compared to the original 24-bit sRGB or YCbCr specified in previous HDMI versions.
Other optional features include output of Dolby TrueHD and DTS-HD Master Audio streams for external decoding by AV receivers; it incorporates automatic audio syncing or auto lip sync capability; and as indicated earlier on, Version 1.3 has brought with it definitions for HDMI Cable categories 1 and 2 - this apart from defining a new mini HDMI connector (Type C) for portable devices.
HDMI versions 1.3a, 1.3b, 1.3b1, and 1.3c mainly updated the list of CEC commands, and added HDMI compliance tests.
HDMI Version 1.4 together with versions 1.4a and 1.4b came brought a number of major additions to the already important additions brought by Ver. 1.3. Most important enhancements related to version 1.4 are:
The addition of a 100 Mb/s HDMI Ethernet Channel (HEC) between HDMI connected devices
An increase in the supported resolution to up to 4096x2160p24 or 3840x2160 at up to 30Hz.
Support for 3D over HDMI—supporting common 3D formats and resolutions up to 1080p
Other enhancements include an expanded support for color spaces designed specifically for digital still cameras like sYCC601 and Adobe RGB, an Audio Return Channel for upstream audio transfers over the same HDMI cable, a Micro HDMI Connector that is almost half the size of a standard 19-pin HDMI connector (sort of the mini USB connector equivalent), and an Automotive Connection System for better in-vehicle HDMI use.
HDMI versions 1.4a added additional mandatory 3D formats for broadcast content, game, and movie content, with support for the frame packing 3D format at either 720p50 and 1080p24 or 720p60 and 1080p24, side-by-side horizontal at either 1080i50 or 1080i60, and top-and-bottom at either 720p50 and 1080p24 or 720p60 and 1080p24.
HDMI Version 2.0 so far completes the relatively long list of HDMI versions released since the first version was released over ten years ago. Mind you, as indicated in our introduction, it is not expected to be available on consumer products prior to late 2014.
The main upgrade over HDMI 1.4 is a significant increase in the supported bandwidth — from 10Gbps to 18Gbps — thus enabling Ultra HD 4K hardware to support 4K video content up to 60 frames per second. While HDMI 1.4 supported 4K result ion, yet with HDMI 1.4, 4K resolution is limited to 3840x2160 up to 30 frames per second and 4096x2160 at 24 frames per second.
The increased bandwidth also means that HDMI 2.0 can carry dual full HD video streams that can be shown simultaneously on the same screen - a feature that is already being implemented on a number of LG and Samsung HDTVs.
HDMI 2.0 is also about improved audio - supporting up to 32 audio channels and up to 1536kHz audio sample frequency, which may appear a bit overdone with present available content. More important instead is that HDMI 2.0 adds the capability to better sync audio to what’s happening on your TV; this feature - termed 'Dynamic Auto Lip-Sync' addresses the issue of delays introduced by the video processing by dynamically adjusting synchronization of video and audio streams without user intervention.
Another upgrade related to HDMI 2.0 is 21:9 aspect ratio support (this is the same as 2.35:1); interesting but not so much important considering the minimal number of devices with a native 21:9 display. It is true that BD movies are 21:9 but in effect these are 21:9 in a 16:9 window.
Worth taking note here that no new cables have been defined with HDMI 2.0; this means that Category-2 HDMI cables (also known as High-Speed cables) should support HDMI 2.0.
Also, at this point, it is not clear if a firmware upgrade would be available to upgrade HDMI 1.4 devices to HDMI 2.0. In reality, this is a manufacturer issue; Sony is saying its products can do this yet there is still no confirmation neither from Sony nor from any other manufacturer that such firmware upgrades will be available for their line of products.
Before continuing further with our discussion on HDMI cables, it would be appropriate at this point to bring out the main similarities and differences between these two digital standards. Both are very closely related in that HDMI uses the same digital encoding scheme used by DVI-D in the transport of digital video.
This explains why all that is required to interconnect a DVI device with HDMI-enabled equipment, is a simple DVI-to-HDMI cable adaptor with a DVI-D plug on one end and an HDMI connector on the other. In this case however, digital audio will have to be carried separately since DVI does not support audio over the same interconnect. This would not be the case in an 'all' HDMI-to-HDMI cable, where the digital audio signal is carried along with the digital video over the same cable.
However, out of the different DVI flavors, HDMI is only compatible with DVI-D format. In other words, there's no way to adapt an analog VGA signal to go in through an HDMI connection as is possible with a DVI-I interface.
Other important differences include:
HDMI cable connectors are substantially smaller than the 37.0 mm wide DVI plug.
The DVI standard was originally developed to be used by PCs, while HDMI was developed by some of the major electronics manufacturers for use in consumer electronic products such as DVD players and digital televisions.
Audio and Video over HDMI: How does HDMI transport digital video and audio over the same HDMI Cable?
We will not go into the actual architecture of how this is done, yet there are a few basics worth knowing about how HDMI transport data and in particular, how this transport mechanism relates to the maximum data throughput or bandwidth, that can be carried over an HDMI cable connection.
HDMI uses the same unique TMDS encoding protocol used in DVI, to transport video and audio information over the same interconnect. TMDS stands for transition minimized differential signaling; it conveys data by transitioning between 'on' and 'off' states while utilizing an advanced encoding algorithm to minimize the transitions necessary to transport data between the HDMI 'source' e.g. an HDMI-enabled digital satellite TV set-top box, and an HDMI-enabled 'sink' device or monitor e.g. a digital television.
Minimizing the required transitions avoids excessive electromagnetic interference (EMI) levels on the interconnecting HDMI cable. At the same time, additional operation is performed to minimize long strings of '1' and '0' which otherwise can cause detection errors. In this process, incoming 8-bit data is encoded into a 10-bit transition-minimized, DC-balanced word.
The HDMI standard specifies both single-link and dual-link HDMI. A single HDMI link is made up of 3 TMDS data channels using three separate differential pairs on the HDMI cable to transport audio and video data at a maximum pixel clock rate of 165MHz (equivalent to 165 million pixels per second); this maximum bandwidth was further increased to 340 MHz with HDMI 1.3 and 1.4.
A fourth differential pair, called the TMDS Clock provides the pixel clock for timing the data stream.
Single-link HDMI is fully compatible with single-link DVI-D - but only at 165 MHz, while dual-link HDMI is compatible with dual-link DVI-D.
Video information is transmitted as a series of 24-bit pixels—8 bits each for each of the primary colors (ver. 1.3 and 1.4 supports up to 48 bit pixel information).
24-bit pixel information is encoded using the TMDS protocol into three 10-bit words per pixel clock period (i.e. each pixel is made up of 30bits). This means that the effective maximum data throughput is 4.95Gbit/s (165MHz x 30-bits) over a single-link HDMI cable for up to HDMI ver. 1.2, or 9.9Gbit/s over a dual-link HDMI interconnect. In the case of HDMI ver. 1.3 and 1.4, maximum data throughput over a single link is 10.2 Gbit/s; this higher maximum data throughput is required to support both the Deep Color feature as well as the increased maximum video resolution supported by these newer HDMI versions.
How much bandwidth do you need? To understand how this 'pixel clock' relates to resolution, let's consider the 1080p 60Hz HDTV video signal. Lets also assume a typical 16% overall blanking interval; this represents the portion of the video signal that occurs at the end of each horizontal line (horizontal blanking) as well as at the end of each frame or field (vertical blanking).
The bandwidth required for a given resolution is governed by the refresh rate and blanking interval of the monitor; bandwidth can be calculated using the following formula:
Resolution x Refresh Rate x [1 + Blanking Period] in Bits/s
where the Blanking Period is the sum of the horizontal and vertical blanking intervals.
This means that in our case, the required bandwidth is equal to 1920 x 1080 x 60 x [1 + 0.16] = 144.4MHz or 144.4 million pixels/sec.
It is thus clear that even HDMI ver. 1 and ver. 2 have more than enough bandwidth on a single link to accommodate even the highest HDTV format most common today. This also explains why dual-link HDMI - like dual-link DVI, has remained practically non-existent
Audio can be from two to eight channels, using sample rates up to 192KHz. Multi-channel digital audio is time multiplexed into the same TMDS data streams used for video; this is possible as audio requires a much lower data rate (max. 192Kbps), and therefore, it can be easily 'stuffed' in between empty spaces available on the data channels.
HDMI also includes two other important channels: DDC and CEC
DDC - Display Data Channel, is used to enable the source device to interrogate the receiving device about its configuration and capabilities. This is done by reading the E-EDID (Enhanced Extended Display Identification Data) data from the receiving device. Data is transferred using I2 C signaling with a 100 kHz clock.
CEC - Consumer Electronics Control Channel, is optional and as already expressed earlier on in the HDMI Cables guide, allows the control of several AV devices interconnected over HDMI. It is mainly used for remote control functions and makes use of the industry standard AV Link protocol transmitted over a one-wire bi-directional serial bus.