Oxygen-free copper (OFC) has been recognised for many years as an
excellent material for use as a conductor. It allows the signal to pass
along its length with minimal loss. Many cables also include two separate
shields — one made of braided copper
which minimises RF interference and
one made of foil to minimise against
EM interference. It stands to reason -
the better the cable, the less the
interference, thus improving
performance.
The plug is an extremely important
Test
April 30, 2008 — yavsHDMI – What is it and how does it Work?
February 10, 2008 — yavsWriter Bryan Davey has written a superb in-depth but not high-browarticle on how and why HDMI cables can benefit A/V consumers.Some will find it interesting while others a little controversial.
Staring at the back of a modern home cinema Receiver or A/V preamp can be a scary thing for inexperienced A/V enthusiasts. The number of connections on a higher end piece can be overwhelming, with multiple video input and output types ranging from composite to component to S-Video and DVI HDMI. The audio options can be just as daunting with toslink, AES-EBU, composite and digital RCA audio connections all filling up a great deal of real estate on the Receiver or A/V preamp. Assuming a user can figure out how to best configure the system and put the right cables in the right connections on the back of the gear, the process is only half over at this point.
“Programming each input of the Receiver/Preamp is a whole task in itself and requires some planning and foresight to be sure that each video and audio input is properly assigned.”
Since all Receivers and Preamps differ in configuration, getting the right audio input and video input lined up properly can sometimes prove difficult. Definitely not a job for the feint-hearted or novice!When all the cables are plugged in and the programming has been completed, even some of the most well thought out cabling set-ups often result in a large rat’s nest of cables cluttering the back of the equipment rack. Surely anyone who has gone through the task of installing a system has said to himself or herself at some point, “Can’t they just make one cable that replaces all of these?” Unless you have been living under a rock and don’t know what HDTV is, chances are you have heard of HDMI and it justmight be the answer to cleaning up a considerable number of these cables and improving the performance of your system.HDMI, which stands for High Definition Multimedia Interface, is the only interface in consumer electronics that can carry both uncompressed high definition video and uncompressed multi-channel audio in all HD formats, including 720p, 1080i and even the granddaddy of them all, gigabit HD 1080p. Besides the technical specs of HDMI that are superior to other video cable formats, the physical connection itself is a much improved design over its predecessors. S-Video cables are the bottom of the barrel when it comes to the quality of the connector. The very small pins on these cables are notorious for getting bent or broken off and have collectively caused more hours of grief than any other connection in all of A/V. Just like computer tech support people are trained to tell customers to try rebooting their systems when problems occur, the number one rule in A/V when you don’t have a picture and are using S-Video is to check to see if one of the pins on the cable is bent. S2Video of course does not transmit HD signal. However, high-end A/V receivers and A/V preamps are now able to video up-convert S-Video signals and output them via HDMI. Before DVI and HDMI, component video was the cable of choice for transmitting megabit 720p and 1080i HD video. The component connection is actually comprised of three separate cables that you commonly see on video displays and sources with red, green and blue RCA connections, labelled Y, B-Y and R-Y. On higher-end pieces, professional grade BNC twist lock connectors are often used. This connection is still commonly used, but it’s an analog connection that requires digital to analog back to digital conversions that cut down on the integrity of the HD signal. Having seen an ISF-certified technician run tests on my display, using the same source viaHDMI and Component into my HD display, he showed me the dramatic benefits to using the HDMI all-digital connection. Editor’s Note: Not all HDMI cables are created equal and therefore results will vary and sometimes significantly.One other negative issue that has kept component video popular for delivering HD content to video displays and projectors is the fact that long HDMI cable runs are plagued by signal loss over 5 metres and over 10 metres for DVI. To overcome this problem, boosters must be used to run a longer than usual HDMI or DVI connection. Systems where the components and display are close together tend to not have this issue, as they are usually located near the source components, but projectors that hang on the ceiling and modern flat panel installations are more often than not well over the 5 metre distance from the source that causes problems with HDMI cables. Some people prefer the screw-on DVI cable to the small, slender HDMI connector. However, I have recently learned to love the simplicity of the HDMI connection when I had to reach my hand into a virtually inaccessible space and plug in an HDMI cable with one hand. It would have been impossible to get a bulky DVI cable plugged in and would have required me to take out most of the components in the cabinet. The HDMI plug is robust enough to let you know when it is properly connected and yet very simple to plug in and out and does not get stuck and require an extreme amount of force as some RCA connectors can do when jammed together in close quarters.What about DVI? HDMI comes on the heels of this previous direct digital HD video cable. HDMI is backwardscompatibleto DVI with the use of adapter of conversion cable. However, now that HD-DVD and Blu-ray have hit the shops with a high definition audio format included, HDMI will really begin to shine. What sets HDMI and DVI apart, besides the obvious different looking connectors on the ends of the cables is the fact that HDMI has the ability to carry an audio signal along with the video signal and other control signals. Both formats carry the HDCP digital encoding that Hollywood movie studios endorse to prevent people from being able to make direct digital copies of high-definition content, but in the real world of installations of HDMI-based systems, this is one of the reliability issues that AV installers are beginning to face.When the signal from a digital source is sent via HDMI, the digital HDCP encoding information is encrypted and sent along with the audio and video signals. At each step of the chain, whether it is sent directly to a monitor or through some kind of switching system, the HDCP “handshake” must be maintained. If the HDCP signal is compromised in any way before it reaches the display to be un-encoded, the picture will simply not appear on the screen. It is important to make sure that any cables, switches and components that you use are fully HDCP compliant. Currently, many HDMI devices exist on the market and most next generation 1080p-capable TVs are starting to include multiple HDMI inputs for those who do not yet have HDMI switching capabilities. There are HDMI switchers available from companies like Kordz, but not all of them pass 1080p video or any audio through them, so when in the far away future HD audio signals such as DTS-HD begin being broadcast along with the video signals, you will want to check with the manufacturer of your switching solution to see if it is able to pass the audio along with it. Currently, this is not an issue as you just run your video and audio separately, most likely using the dedicated digital outputs of your satellite receiver, cable box or DVD player and running them into your receiver or A/V preamp to be properly decoded.The Blu-ray vs. HD-DVD battle is still raging on, but one thing is certain: the studios have all agreed that HDMI is their approved standard and although there are a few little hurdles including switching, length of cable runs and the HDCP encoding issues, there are solutions to almost every setup issue. Receivers with multiple HDMI inputs and digital amps inside will start to become smaller, as the massive amount of real estate for connectors will not be needed as much. The high bandwidth promise of 1080p video will take HDTV to the next level and, although it is not a perfect connector, HDMI is the new standard that will be transmitting it and it’s going to be here to stay for a long time.
LCD TV – How they work
December 10, 2007 — yavs
An LCD TV is sometimes referred to as a “transmissive” display – light isn’t created by the liquid crystals themselves; a light source (bulb) behind the panel shines light through the display. A white diffusion panel behind the LCD redirects and scatters the light evenly to ensure a uniform image. The display consists of two polarizing transparent panels and a liquid crystal solution sandwiched in between. The screen’s front layer of glass is etched on the inside surface in a grid pattern to form a template for the layer of liquid crystals. Liquid crystals are rod-shaped molecules that bend light in response to an electric current – the crystals align so that light cannot pass through them. Each crystal acts like a shutter, either allowing light to pass through or blocking the light. The pattern of transparent and dark crystals forms the image. It’s the same display technology behind your digital watch but way more sophisticated.
LCD TVs use the most advanced type of LCD, known as an “active-matrix” LCD. This design is based on thin film transistors (TFT) – basically, tiny switching transistors and capacitors that are arranged in a matrix on a glass substrate. Their job is to rapidly switch the LCD’s pixels on and off. In a color TV’s LCD, each color pixel is created by three sub-pixels with red, green and blue color filters.
One of the biggest challenges for LCD TV manufacturers has been speeding up the “pixel response” time (how fast an individual pixel’s color can change without blurring) to ensure that fast-moving objects don’t exhibit “motion lag” or ghosting. It’s especially critical for larger-screen LCD TVs where much of the viewing will be DVD movies and/or HDTV. An important difference between plasma and LCD technology is that an LCD screen doesn’t have a coating of phosphor dots (colors are created through the use of filters). That means you’ll never have to worry about image burn-in, which is great news, especially for anyone planning to connect a PC or video game system. LCD TVs are extremely energy-efficient, typically consuming 60% less power than comparably-sized tubetype direct-view TVs!
