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What TV Specifications Really Mean

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In years gone by purchasing a TV set was relatively easy, pick the best size that fit the room and budget and buy it.  In today's era of flat panel HDTV's reading the specification sheets can make some buyers feeling like they are reading an foreign language.  

Viva La Resolution: The most common specification that is marked on the TV boxes and on the TV’s themselves on display in retail stores is the resolution, simply the resolution is the number of rows of pixels a TV display hasfrom top to bottom.  Standard definition displays such as the classic picture tube TV’s have 480 rows of pixels. High Definition displays will have ether 720 or 1080 rows of pixels or lines as it is also known.  Smaller screens anything smaller than 32” are typically going to be capable of displaying 720 lines of resolution but there are some models as small 24” that can display 1080 lines of resolution. TV’s 40” and larger will be able to display 1080 lines of resolution.  

Minding your P's & I's: One of the first statistics listed on the specification sheet is going to list is the resolution support.  The old fashioned tube TV's that we knew and loved in decades gone by displayed 480 lines. The number refers to the rows of pixels a TV displays. The letters P or I refers to progressive scanning or Interlaced scanning.  To understand the difference take the old style as an example.  Elections are shot at the front of the tube coated with phosphorus causing it to glow.  The beam of elections is deflected by electromagnets the beam to scan across the face of the picture tube from side to side starting at the top and moving to the bottom.  One problem with this is that the phosphorus dims very quickly once the elections stop hitting it.  Interlaced scanning addresses this by scanning all the odd numbered lines in 1/60 th of a second and then scanning the even numbered lines the next 1/60th of a second.  Progressive scanning on the other hand draws all the all the line all within 1/60th of a second. A video signal at 720p contains 60 frames in each second of video.

Don’t Tell Me Because It Hertz:  In the explanation of progressive and interlaced scanning, how a television draws it’s picture was explained.  The number of times within a second this happens is called the refresh rate, it’s measured in hertz.  Picture tube TV’s and earlier generations of flat panels had a refresh rate of 60 hertz.  A few years ago TV’s came on the market that refreshed their displays at 120 hertz.  To take maximum advantage of a faster refresh rate a signal source has to have more frames to match the refresh rate of the TV.  Currently the only source that can send video at 120 Hz are computers, since most flat panels have VGA inputs which allows TV’s to be used as computer monitors.  
All other sources of broadcast or pre-recorded material from antennas, cable, satellite, DVD’s and Blu-Ray discs have video that refreshes at 60 Hz, making the faster refresh rate redundant.  While some retail sales staff may claim that 120 or 240 Hz refresh rate is supposed to make the picture sharper the truth is that the same frame is being re-drawn two or four times.  Some TV manufacturers are building in frame interpolation, a technology where an internal processor tries to create the frames that go in between the actual frames from the incoming video source.  While some maintain that this creates a sharper picture, while others see a picture that appears to be jittery, sped up or shot with a home camcorder.  It would requires looking TV in the store set at both 60 and 120 hertz to decide if 120 hertz is really beneficial.

Response Time: Response time is length of time it takes an LCD display to turn a pixel on or off.  Typical refresh rate for a modern LCD TV set is 6 milliseconds high end LCD panels typically have refresh rates around 3 milliseconds.  Older LCD panels had refresh rates of 12 milliseconds or more, which lead to frequent motion blurring. To get an LCD TV with the sharpest picture look for the lowest response time not the higher refresh rate.

Tuner Types:  In order to access most signals available TV sets have a circuit called a tuner that takes the signals received by an antenna or delivered through cable and decodes the video and audio signals.  For the first 50 years of television the analog tuner called an NTSC tuner changed very little.  About a decade ago tuners that receive digital signals officially known as ATSC became a part of modern TV sets.  The ATSC tuner is required to pull in the digital signals broadcast by TV stations.  NTSC Tuners while not needed for receiving over the air broadcasts, are still included in televisions sets to display the output from legacy video devices such as VCR’s and early generation video game consoles.

Input Input Input:  Inputs are simply the types of interface types that a TV can accept.  The most common type of signal input is the 75 Ohm RF jack.  Just about every TV on the market has just one of these.  This the the jack on the back that a coax cable from an antenna or a direct analog feed from a cable TV service provider attaches to.  Composite video is the next most common type of Video and Audio input found on TV sets. These are the set of RCA jacks that are typically coloured yellow, white and red.  Composite video carries standard definition video and stereo audio from legacy video devices such as VCR’s and older generation video game consoles.  S-Video carries standard definition video with better picture quality than composite video can carry.  DVD players and some camcorders have S-Video outputs.  When using S-Video a separate red-white RCA cable is required to carry audio.  Component video separates video signal information to and sends it over three different wires.  Component video uses RCA plugs and jacks coloured red, blue, and Green.  As well as providing picture quality that is vastly superior to composite and S-Video for standard definition video, component can carry 1080i and 720p high definition video signals as well.  Just like S-Video a separate connection for stereo audio is required with component video.  HDMI gives the best performance out of all the other types of inputs because the signals carried by HDMI are all digital.  HDMI carries both High Definition video as well as audio signals over a single cable eliminating for a separate patch cable for the audio.  Blu-Ray players, modern generation video game consoles and HD digital cable and satellite receivers connect to TV’s using HDMI.


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