Saturday, January 1, 2011
【 Weak current College 】 home theater digital interface controversy 】
1 DVI: from computer field to home audio and video environments
In a few years ago, the industry looks forward to your computer and home audio and video electronics combine to become inseparable whole, free and interconnection in order to achieve better entertainment features. This was just a dream, computers and home environment of audio-visual products there is a huge obstacle. Computer to digital technology, all data are expressed in binary number, and home video products in simulation technology, all images, video, audio, information is through continuous expression of sinusoidal signals. Because the underlying signal representation exist fundamental differences, both control circuit also belong to a different system, most can only be achieved by converting analog basic information sharing, far from collaboration. This restriction until digital display technology has begun to audio-visual area before gradually changing, specific point that is in the plasma TV, LCD TV products are popular as well as digital TV standard commences, computer and audio-visual electronics communication collaboration can become possible, this is also the core of the concept of the digital home.
However, today we are going to discuss is not how the two systems, but is concerned about the collaboration for the digital home environment used by the data transfer interface. For example, how computers and digital TV connection? DVD players, DVR, and soon-to-market of Blu-ray player/HD DVD player with digital display technologies that adapt? currently widely used analog transmission interface nature cannot continue, the introduction of new interface technology is imperative. DVI and HDMI ultimately bear the burden, both in technology, there are very different, they all get the support of many manufacturers, thus forming the coexistence of two interfaces.
DVI: from computer field to home audio and video environments
For DVI interface everyone, it is widely used in computer monitors, LCD was introduced to the audio-visual area may let a lot of people feel fresh. For a long time, home audio and video environments are simulation technology-based, as the video output to a TV and an audio output device's speaker, without exception can only handle and receive analog signals, DVD, CD player and other digital devices must advance the video or audio signal into analog format, and then were transferred to the CRT TV or audio device. Due to the analog signal is not present, the concept of data transfer rate does not require complex interface bus, simple copper conductor wires and coaxial interfaces to meet your needs, this is the last home audio-visual environment standards mode. But when the LCD TV, plasma TV, digital home concept is great, the industry has found that continue to use analog interface is a very silly, because as the signal outputs of DVD players, DVR, and as a signal receiver TV is based on a digital system, and then use the analog interface not only increase costs, signal quality and do not prevent the loss, the timely introduction of a specialized digital interface is imperative.
Tailored design for LCD monitor
DVI interface becomes the first consideration of the object. The interface specification from Intel, Silicon Image, Fujitsu (Fujitsu), Hewlett-Packard, IBM and NEC, and other companies that are "working group" digital display DDWG (Digital Display Working Group) jointly developed, leader for Intel Corporation. The full name is "a DVI Digital Visual Interface", for "digital video interface," 1.0 standards as early as in April 1999 was officially released.
In the underlying technology, DVI digital interface technology takes on DFP (Digital Flat Panel), is built on TMDS signal format — TMDS (Transition Minimized Differential Signaling) is a differential signal mechanism that can encode the pixel data, and are transmitted through the serial mode, with the help of this technology, an uncompressed digital video signals can be smoothly transferred to appear directly on the LCD display. Theoretically, DVI is undoubtedly the best partner of the LCD, but early LCD monitor products must take into account the problems with video card compatibility, then the video without exception are using VGA analog interface, LCD monitor has to select VGA. To do this, display the control circuit must be more than one ADC. As a result of the conversion process will necessarily produce distortion to a large extent affected the LCD display. This situation with the LCD with the increasing popularity of slowly changing video card with DVI interface, new-to-market growing number of LCD monitor also uses DVI, VGA dual interface, which the computer is displaying the system begins to realize from the analog to the digital transition. Up to now, the mainstream LCD monitors are basically DVI interface with the world.
Although DVI is designed specifically for computer monitors the design, but it is equally suitable for a family of digital audio-visual environment, we can see, LCD TV or plasma TV that receives digital video signal and computer graphics, monitor the processing of digital signals and no essential differences, coupled with DVI support "Plug and Play (with plug)" and auto-correction function, signal can make image signal sources and different display output devices allow resolution of coincided, scan frequency, these features make DVI in theory as consumer electronics product image transmission interface. Of course, in the specific implementation, DVI connector must also be changed for compatibility.
Smoothing applied to digital audio and video environments
However, digital television and computer monitor in the display mode is not the same, on transmission interface bandwidth requirements also vary. Then, the bandwidth provided by DVI can meet the actual needs of the HDTV signal?, in fact, such worries are completely unnecessary. On-line display mode of the flat panel display, if the refreshrate is set at 60Hz, DVISupports 1600 × 1200 high-resolution output (that is, UXGA standard, the higher the refresh rate, and supported screen resolution is lower). For interlaced display of digital television signals, DVI supports to 1920 × 1080 resolution, which is also the highest standards of HDTV. In addition, DVI support a "dual link DVI (DVI dual-link)" expansion mode, it can support 60Hz refresh rate 2048 × 1536 (QXGA) for ultra high resolution output, however the present rare products can meet this requirement, DVI of the extended features of basic school not handy. To be applied to consumer electronics, DVI also adds a "high-bandwidth digital content protection (High bandwidth Digital Content Protection, called HDCP)" encryption protocol. The agreement of the initiator is the large Studio in Hollywood, as well as satellite/cable TV companies, which can effectively prevent DVI video signal to be pirated, a third party in the transport sectors to avoid possible image piracy. HDCP is technically not mysterious, it's a popular encryption/decryption validation mechanisms, in addition to the DVI interface required to support this feature, the display Terminal receiver logic must also provide support to it, such a display Terminal from digital set-top boxes, DVD players, and other signal output side receives and displays those close protection of image content. To the DVI interface with the general distinction between DVI HDCP protocol interface is also called "DVI-HDTV".
Although not tailored for audio-visual environment, but the DVI interface in this area still has many advantages: first, the DVI connector on the LCD monitor, projector and other equipment in the highly popular, consumer electronic device with a DVI connector, you can achieve smooth shared resources, for example, we can use DVD player, digital set-top box and the computer is directly connected to the monitor, projector, which obviously greatly expand the scope of application audiovisual entertainment; second, DVI technology is mature, sophisticated facilities, equipment design difficulty and manufacturing costs are relatively low, which reduces the overall digital audio-visual environment is very conducive to building costs. For this reason, many other audio visual companies take the lead in the high-end products introduced into the DVI interface, these products include professional DVD players, DVR, digital set-top box, LCD TV, plasma TV, projector, etc. In practical use DVI interface well, plus the related equipment is very popular, very well meet the digital audio-visual environment on the urgent needs of digital interfaces.
In practice the deficiencies in the
However, DVI are specially designed for computer monitors, and not excessive taking into account the needs of digital audio-visual environment, some birth defects in the practical process unfolding. First of all, DVI is only a digital video interface, it is unable to transmit the audio signal, and digital audio and video environments both is one. In this way, the audio signal transmission with simulation, this may affect audio output, especially of fidelity SACD and DVD Audio now has started to replace the CD technology been in use for many years, to continue to transfer audio signals in analogue interface, SACD and DVD Audio with high-precision digital audio effects will diminished, it is obviously difficult for those on the HiFi audio quality picky about customer satisfaction. Secondly, the DVI interface spec confusing exist DVI-A, DVI-I, DVI-d and is developing DVI-E, and other specifications, including General analog signal DVI-A support, DVI-D support digital signal, and the support DVI-I analog, digital-signal, standard classification confusion, the average entry level users can easily choose to interface specification for different products, cause they are simply unable to use together. In addition, a large number of products that do not support HDCP encryption protocol, really can meet DVI-HDTV norms in a minority, which also give users a lot of trouble. Once again, the DVI connector on the length of the connecting line is more sensitive, although the DVI standard specification does not specify the length of the cables, but generally considered DVI connector should be no longer than 5 meters, otherwise there will be a significant drop in picture quality, the longer the line length, picture quality, the more damage. On a computer monitor, 5 m length is very comfortable, but this is not the case for audio and video products. In General, home theater, more than 20 meters required connector is commonplace, but a small number of high level home theater environment even more than 30 meters of cable length, DVI interface is indeed very difficult to meet these requirements. But fortunately, the industry has made positive efforts, we can use two methods to resolve this problem. The first method is to use Monster Cable companies sell DVI cable, the company structure through improved cable and use the best materials, successfully produced length up to 20 m DVI cable. Although reach the default length of 4 times, but this DVI cable will still be able to maintain excellent signal quality. The second method is to use Theatre Automation Wow (TAW), Gefen, Goldmund or OPHIT corpoation fibre DVI cable, as the name implies, this type of cable in the Middle link uses the fiber as a signal transmission medium, for maximum signal fidelity, while its maximum length up to 100 meters, almost any environment. However, fiber optic DVI cable structure is complex, turning connector location require optical/electrical converter, the price is quite expensive, I am afraid that the average user.
2. HDMI: tailored for the digital home
Because there are a large number of DVI interface, the industry generally believe it only as a transitional standards. In order to better meet future digital audio-visual environment of actual needs, proposing a new interface technologyis imperative, that is our next to introduction of HDMI high-resolution multimedia receivedEstuary.
Technical implementation and features
With DVI, HDMI is a beginning to digital audio and video area specially designed, it's full name is "High Definition Multimedia Interface," which means "high definition multimedia interface." Sponsors of the HDMI standard is Hitachi, Matsushita (Panasonic), Philips, Silicon Image, Sony, Thomson (Thomson) and Toshiba Corporation, 1.0 standard in December 2003, officially announced, in order to better promote the practical, Enterprise HDMI jointly set up HDMI (HDMI Working Group). In fact, before the introduction of the standards, HDMI has access to many Hollywood Studio and satellite TV industry as well as consumer electronic manufacturers, it is by virtue of their own have a range of excellent features.
In signal transmission, HDMI is a DVI-based, both in the video signals of the pins on the exact same definition, the difference is that DVI only transmit video and synchronization signals, but HDMI is on this basis increased transmission multichannel digital audio capabilities. Thus, the audio signal is also completely to the transmission by digital means, SACD, DVD Audio, and other next-generation digital audio quality HiFi equipment can remain in the best condition. More advantageous is that HDMI home theater environments as long as you use an HDMI cable to transfer all of the video/audio signal, and DVI and analog environment now sharp contrast. If a DVI connector, digital audio/visual environment still requires the use of multiple analog audio cables, but now the analog AV, not to mention the environment. Visible, HDMI in providing excellent video/audio signal quality, but also for home audio-visual equipment installation work easier.
In order to meet the high-definition digital video and high-fidelity audio data transfer, HDMI transmission bandwidth is designed to 5Gbps, which is sufficient to cope with a resolution of 1920 × 1080 (interlaced) HDTV video and an 8-channel, 96kHz or Mono 192kHz digital audio transmission. In support of the highest resolution, HDMI also can support the YCrCb color space — we need to make a simple explanation: computer monitors typically use RGB color space, red, green and blue color; PAL TV system you use YUV color space, it is equivalent to the RGB space made a related linear change, they can be converted by a formula, in which the brightness, y, U and V ratio determines the tone, (U2 + V2) 1/2 represents the color saturation. As for what we call the YCrCb color space, it is actually derived from the YUV, and is intended for digital TV systems. DVI-HDTV interface although can also support digital television by the YCrCb color space, but it cannot achieve at the highest resolution, which receive HDTV signals, color space must be translated in the transport links, this will inevitably lead to a certain degree of color distortion. HDMI is fully fixed this, during the transfer process color space without conversion, the screen shows the natural color of picture quality. In addition, HDMI is fully HDCP encryption protocol included with the interface of audiovisual equipment can be successfully receiving display strong protection of multimedia content, and DVI connector on the protocol supports chaos is also a striking contrast.
Although and DVI pin-compatible, but HDMI and DVI and cannot directly swap, because both interfaces encapsulate, HDMI DVI interface connectors is less than, we can contrast from Figure 2 clearly seen in — smaller connector is conducive to the PCB wiring and impedance matching. While both of these interfaces can use a dedicated passive connector (passive adapter) for transfer, but in the transfer process, HDMI in, based on the new DVI audio functionality will be lost, only the video signal can be retained. This device is very important in the utility, after all, the market of consumer electronics products to DVI connector,use DVI-HDMI passive connector, you can implement two interfaces smooth transition between devices.
The transmission distance, HDMI DVI are compared to the considerable improvement. Standard DVI cable length is limited to 5 meters, while the standard HDMI cable lengths up to 25 meters, is the former 5 times, you can very well meet the needs of the vast majority of home users. For those who have the luxury of a large space theater, you can also use the extension cable HDMI cable even fibre, because HDMI cabling is simple, the advantage in these areas.
Uniform standards of compatibility tests to avoid confusion
In order to avoid similar DVI products of disarray, HDMI working group developed a rigorous compatibility test specifications (Compliance Test Specification, or CTS), all HDMI products must be certified through the specification before playing on the HDMI logo. To this end, the HDMI working group set up two certification test center (Authorized Testing Centers, ATC), a test center located at ribensongxiagongsi, another test center are located in the Silicon Image company, which is also the HDMI interface controller's main provider. Manufacturers in product design has been completed, prior to production of the prototype is submitted to one of the ATC testing, test content including HDMI transmitter, receiver and transmission cables, some AV receiver product (A/V Receivers) as long as the test for HDMI signal reception. Only passed the practical function of inspection, to get the HDMI trademark images (logo), but all certified products are compatible with each other. Because all the production equipment manufacturers have HDMI complianceThis certification specifications, sales of various products can be smoothly HDMI connections use, not what bothers to consumers. In contrast, DVI although some authentication mechanism, but is not mandatory, the manufacturer's attitude is not positive, leading to DVI compatibility issues layer out of the infinite that until now have not been fundamentally improved. From this perspective, HDMI over DVI interface, which is difficult to escape the substituted fate.
Although 1.0 standard in December 2003, before publication, but HDMI as early as practical process with the early start, Silicon Image company played a crucial role. Silicon Image's HDMI a founding member of the Working Group, it is mainly responsible for HDMI transmitter and receiver chip design. In early 2003, Silicon Image just launched called "PanelLink Cinema" HDMI transmitter and receiver, the product launch, rapidly as Samsung, Panasonic, Meridian, Enterprise, which, in the same year, a quarter of Meridian will launch with HDMI interface high-end DVD player, Panasonic will start sales in September with HDMI input and compatible DVI HDTV television of rear projection, Samsung provides HDMI digital set-top box. But so far, the use of HDMI products is still not too much, DVI in absolute numbers or occupies a dominant position, the reason lies in the presence of preconceived advantage DVI, equipment manufacturers and when we decide to use DVI interface, all the products in the future will be based on the system, DVI HDMI camp hard to convince these enterprises are costly to the HDMI interface. Furthermore, consumers just have a DVI device, when you purchase your other device must give priority to using DVI interface products, consumption of inertia make DVI still owns a broad market space, although technically HDMI outgo DVI.
Secondly, the interface is more expensive but also hinder the HDMI universal one of the important factors. At present, a high-quality HDMI connector retail price over $ 100, and the quality of the ordinary, 2 m length of HDMI connector also need 20 dollars, consumers are hard to bear. Worse, there is no electrical appliances can support a 8-channel audio, current TV generally only need two-channel, HDMI's eight channels of digital audio transmission capacity in the basic school not handy, it is also a blow to the enthusiasm of many manufacturers. Considering the consumer electronics industry update, HDMI is slow in the short time I change that is difficult to estimate DVI's dominant position in the next few years will remain, but HDMI can slow the pace of expansion.
3. digital home theater interface controversy
Although facing difficulties, DVI HDMI as a replacement for the status remains not shake. Long-term trends, home theater environment is bound to achieve fully digitized, DVI connector cannot bypass analog audio transmission bottlenecks at this point, the HDMI yards. With HDMI, we can use DVD players, DVD recorders, digital set-top boxes, D-VHS player, audio receivers, digital source devices and digital TV, PDP displays, LCD TVs, projectors, digital display devices connected to realization of the all-digital high-quality audio output. It is not difficult to imagine that this transition process may be long and painful. For compatibility with existing DVI device, HDMI products must be in addition equipped with DVI adapter interface, or simply provide HDMI/DVI dual interface forms, this field with the LCD monitor's DVI/VGA dual interface morphology similar. With support for HDMI device is gradually increasing, its popularity is growing rapidly, in contrast, DVI interface influence will be shrinking, maybe in the next five to ten years, we have the opportunity to see this.
For those who are ready to start from scratch building a digital home theater friend, select HDMI must have been a wise idea, provided that you do not have any liability to the DVI device, or is willing to go through the DVI interface implements device compatible. But if you have many products based on DVI interface, our proposal is honestly select DVI environment for good, after all, through the transfer of the form you will not only unable to experience the benefits of HDMI, but need to pay more money. At last, we need to reiterate: DVI or HDMI interface, are insufficient to on audiovisual equipment quality have a decisive impact, after all, they simply transfer interface, audiovisual equipment quality how to more depends on the design of the product itself.