Questions & Answers:
Digital & Analogue Audio/Video Signals... |
| Digital and Analogue Audio/Video Signals |
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| DVI |
| Stands for Digital Visual Interface and is an industry standard for Digitally transmitting RGB signals to digital displays such as LCD monitors, Plasma screens and projectors. There are two basic forms – DVI-D and DVI-I; DVI-D is only capable of carrying digital signals whereas DVI-I has several extra connections within the cable that gives it the ability to carry standard analogue RGB signals too.
In the context of Home Cinema - DVD players take Digital information from a DVD, convert it to an analogue signal for transmission, then have the display convert the signal back to digital again in order to reproduce the image. When using a DVI connection the signal remains digital throughout and as such doesn’t suffer loss incurred through analogue to digital conversions.
The DVI standard is defined as either dual-link of single link. Single link uses 12 of 24 pins in the cable giving a bandwidth of 165MHZ which will transfer resolutions up to 1920 x 1080 @ 60Hz and 1280 x 1024 @ 85Hz. Dual-Link will use all 24 pins doubling up the bandwidth to two 165MHz channels. This is capable of transferring resolutions up to 2048 x 1536 @ 60Hz and 1920 x 1080 @ 85Hz!!
See http://www.ddwg.org for information on the DVI forum
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| iLink |
| Essentially, iLink is the computer IEEE 1394 or Firewire standard. A Digital data transmission medium that is capable of transferring data at up to 400Mbps. In the Home Cinema context it is limited to 100 or 200 Mbps, and is commonly used either for transfer of Digital Video (DV) material from camcorders to DVD recorders and PCs, or for the transfer of Advanced Resolution Audio – 6 channels of uncompressed 192Kbps digital audio (notably useful for high-resolution audio formats such as SACD or DVD-Audio in addition to transferring Dolby Digital and DTS). |
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| HDMI a brief explanation |
| HDMI brings the relative advantages of DVI and iLink into one industry-supported, consumer product. In it’s basic sense a HDMI lead is essentially a cable that carries DVI style video and iLink style audio (early revisions limited to 2 channel, V2 carries 8 channel audio). Unlike DVI, HDMI can also send interlaced images, and is capable of running over longer cable lengths to DVI (expect 15m – twice as long as DVI).
Typical applications are from DVD to plasma/projector, and soon this will run via your AV amp which will pick up the audio stream. For more information see http://www.hdmi.org/consumer/faq.asp
Going Digital does not guarantee you a good picture or sound. While there may be no loss during transmission, if the signal was poorly constructed to start with it is still going to be poor when output. i.e. cheap DVD players with DVI connections are still cheap DVD players!
We have also prepared a Questions and Answers PDF for HDMI, which can be downloaded here
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| Analogue Transmission |
| A video signal, no matter what type, must contain the colour detail and a synchronisation signal (to tell the display how to put the colours together). In some cases the colour is split into the whole picture in black and white (Luminance) plus the colour streams for the signal (Chrominance), again the synchronisation tells the display how to put all this together. |
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| Composite Video |
| Basic form of video used with VCRs, Laserdisc and other basic technologies. As the name might suggest all the various video signal components are sent down one single coaxial cable (usually with a Yellow “Phono” plug at the ends). This format is cheap and easy, and will run over very long distances – however, since all the components are running down the same single cable they interfere with each other and produce a flawed picture. |
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| S-Video (SVHS, Super VHS, Separated Video) |
| As an upgrade to Composite Video (and a far cheaper alternative at the time to RGB video) s-video offered an advantage over composite video by separating the Chrominance information (colour portion of the image) from the sync and Luminance (black and white detail). Although it looks like one cable, s-video actually runs down two coaxial poles within a single, larger, sheath. The cable is terminated with a very familiar 4-pin DIN – a circular plug with four small pins inside. |
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| Component Video (YUV, YPbPr, YCbCr) |
| Component video runs down three separate coaxial cables, one carrying Luminance (black & white detail), and Chrominance (colour stream) being divided into the other 2 cores - Red Chrominance and Blue Chrominance. The sync signal is sent with the Luminance. This is one of the best signal formats, not least of all because it is in this format that information is recorded onto the DVD disc in the first place! It is also capable of sending Progressive Scan signals too. |
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| RGB Video |
| RGB Video is also sends a signal as its separate components, and offers the same quality as Component Video. The three basic colour components (Red, Green and Blue) plus a sync which is either run along the Green component, or as a separate sync, or as two separate syncs; one for horizontal and one for vertical (PC display systems use this). The most common use in the consumer environment is RGB with a separate single sync, and is commonly found on DVD players, Digital set top boxes and the like. While it is possible to run Progressive Scan RGB this is very uncommon in consumer applications with component being the industry-wide choice. |
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