Audio Video Formats Demystified
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Contents |
Introduction
I see all sorts of questions concerning what the difference is between types of cables and what the difference is between 720p and 1080i etc. I had written this description up a while back and though it would be beneficial here, so I've added a bit and made it a little more coherent.
Video
What is "HD"?
HD stands for High Definition. HD is really just a resolution standard for your TV... they list these resolutions by the vertical pixel count and whether or not the picture is interlaced or progressive scan.
Progressive Scan vs. Interlaced
Imagine the picture on your TV is drawn like your computer's printer, one line across at a time. A progressive scan picture draws these lines in order [1,2,3,4,5...] while an interlaced picture does the odds first then goes back and does all the evens [1,3,5,7,9... then back to the top and 2,4,6,8...]. Its generally considered that progressive scan image is superior in quality to a interlaced image of equal resolution. Also TV standards dictate that the various TV formats have a "refresh rate" of 60Hz... that means that a single update pass from top to bottom happens at a rate of 60 times per second. Because interlaced images only update half of the screen in a single pass, it takes 2 passes to update the entire picture. Alternatively progressive scan images update the entire screen in a single pass. Meaning that a progressive scan image updates twice as fast as an interlaced image. So not only do progressive scan image have greater clarity but they also have greater fluidity especially when items being displayed are fast moving.
Aspect Ratio
The Aspect Ratio is basically the relationship in length between the width and the height of the video. There are two basic aspect ratios. Widescreen which has a ratio of 16:9 and FullScreen which has a ratio of 4:3. If you do some simple math it can be deduced that widescreen is 1/3 wider than a Fullscreen counterpart of the same height.
NTSC vs. PAL
NTSC and PAL are variations in video formats specific to certain regions of the world. NTSC stands for "National Television Systems Committee" and PAL stands for "Phase Alternating Line". PAL is also sometimes referred to as SECAM which stands for "System Electronic
color Avec Memoire" (it's French if you couldn't guess)
The NTSC format is used in North America, Japan, Philippines, Taiwan, and other countries. The PAL Format is used in most of Europe, most of Africa, South America, Australia, most of Asia, and other countries. Sometimes the region formats are listed as NTSC-NA or NTSC-J etc to differentiate the difference between a video meant for North America or Japan respectively, but there is no actual difference in the technical aspects of the signal.
Aside from where they're used the Major technical difference between NTSC and PAL is the refresh rate (the rate in which the screen's picture updates).All NTSC standards have a refresh rate of 60Hz while most PAL standards have a refresh rate of only 50Hz. However, some PAL countries use 60Hz because of this you will often see it listed as "PAL-50" or "PAL-60" to delineate between the two. There are other differences between the two when viewing SDTV and EDTV resolutions which is covered below.
Video Formats
There are 3 formats of TV: SDTV, EDTV and HDTV
SDTV
SDTV is Standard Definition TV which is 480i (576i for PAL).
So the image is interlaced with a 640x480 resolution or 720x480 if it's widescreen (640x576 and 720x576 respectivly for PAL)
EDTV
EDTV is Enhanced Definition TV which is 480p (576p for PAL)
So it's similar to SDTV except the image is progressive scan instead of interlaced
again it's 640x480 for square screens and 720x480 for wide screens (640x576 and 720x576 respectivly for PAL)
HDTV
HDTV is High Definition TV which can be either 720p or 1080i (and eventually 1080p) 1280x720 progressive scan and 1920 x 1080 interlaced respectively Depending on who you talk to some will claim that 720p is better than 1080i and visa versa. Most TVs will only support one or the other. When 1080p becomes mainstream there will be no contest. These formats are available in WIDESCREEN ONLY.
Video Cables
Composite
Composite video cables Often referred to as "RCA" cables (because they're itentical to the RCA Audio cables) are the lowest quality cable you can get, this is a single pin Yellow dongle cable typically found alongside the Red and White RCA audio connectors. The entire video signal is contained on a single wire within this cable. This cable only supports SDTV.
S-Video
S-Video is a significant improvement over Composite; Luminance (Contrast Information) and Chrominance (Color information) have been separated to improve clarity. This cable also sports a yellow dongle and is typically found along side the red and white audio connectors. This cable only supports SDTV. S-Video is Only Available in NTSC countries.
Component
Component Video is a dramatic improvement over S-Video and Composite. This breaks down the signal even further for greater quality. This is a set of 3 cables with Red Green and Blue dongles that look similar to the composite connector. Despite the colors being Red Green and Blue in the NTSC standard they aren't actually broken down color wise like that. The Green cable is "Y" Which carries Luminance info similar to that of an S-Video cable. the Blue ("Pb" or "Cb") and Red ("Pr" or "Cr") cables carry the color signals. This cable supports SDTV, EDTV, and HDTV.
RGB
RGB is an older format sometimes the connector looks like a VGA computer connector sometimes it it is split out over 3 cables colored Red Green and Blue with BNC type connectors (push on a twist lock). Unlike Component, these cables actually represent Red Green and Blue. On occasion the 3 RGB cables are accompanied by a 4th "C-Sync" or simply "Sync" cable that determines the refresh rate of the image. This Cable supports SDTV, EDTV, HDTV and various computer resolutions.
SCART
SCART stands for "Syndicat des Constructeurs d’Appareils Radio Recepteurs et Televisieurs" (again French). Scart Carries both Analog Audio (see audio section below) As well as Composite Video and can be configured to carry either RGB Video or S-Video type signals all in the same cable. SCART cables support SDTV, EDTV, and HDTV signals. SCART cables and connectors are only available in Europe and other PAL countries.
VGA
VGA stands for "Video Graphics Adapter". I'm sure you're familiar with VGA as the connector most use to connect their PC to their monitor. VGA is very similar to RGB except not only are the colors broken down separately but the vertical and horizontal syncs are broken down as well. This is only ever found an single cable with a 15 pin connector (usually Blue). This Cable supports various computer resolutions
DVI
DVI Stands for "Digital Video Interface". DVI is the first True Digital Interface. All previously mentioned cables are analog video data while DVI supports digital video data. There are 3 versions of DVI cables DVI-A, DVI-D, and DVI-I. DVI-I supports both analog and digital data while DVI-A and DVI-D support ONLY analog or digital data respectively. The analog data that can travel through a DVI-I connector is the same as VGA. This cable typically has a narrow wide White connector that looks like a squashed version of a VGA connector. If you have a True Digital video screen such as a DLP projector or LCD TV (or LCD computer monitor) DVI-D or DVI-I (carrying a digital signal) is the purest video connector for you, This Cable supports SDTV, EDTV, HDTV as well as computer resolutions.
I should note that the digital signal carried through DVI supports encryption called HDCP (High-bandwidth Digital Content Protection). Because of the protection offered by HDCP Most next generation HD video formats (HD-DVD and Blu-Ray Disc) will only offer HD video through digital interfaces that support HDCP.
HDMI
HDMI stands for "High-Definition Multimedia Interface". HDMI is essentially a smaller version of the DVI-D connector with Digital (S/PDif) Audio built in as well(see audio section below). A single Hi-Definition cable for Audio and Video. This will most likely be the cable standard of choice for a while. This Cable also supports SDTV, EDTV, and HDTV. HDMI also supports the HDCP encryption standard
Audio
Channel Numbering
You may see listings like "5.1" or "7.1" but what does it actually mean? The number before the point refers to the number of "satellite" speakers, which are typically cover the mid to high sound range. The number after the point refers to the number of low frequency speakers, typically sub-woofers. It is generally accepted that if no sub-woofer is being used the satellite speakers are outputting the full range. So if you were to see:
1.0 -front-center
2.0 -front-left and front-right
2.1 -front-left, front-right, and sub-woofer
3.0 -front-left, front-right, and front-center
3.1 -front-left, front-right, front-center, and sub-woofer
4.0 -front-left, front-right, front-center, and rear(two speakers with identical outputs)
4.1 -front-left, front-right, front-center, rear(two speakers with identical outputs), and sub-woofer
5.0 -front-left, front-right, front-center, rear-left, and rear-right
5.1 -front-left, front-right, front-center, rear-left, rear-right and sub-woofer
6.1 -front-left, front-right, front-center, rear-left, rear-right, rear-center, and sub-woofer
7.1 -front-left, front-right, front-center, rear-left, rear-right, rear-center(two speakers with identical outputs), and sub-woofer
Why only one sub woofer?
Low frequency noises are "non-directional" meaning that the human ear cannot typically determine the direction in which the sound is coming from. Under this theory it shouldn't matter where we place the sub woofer or how many sub woofers we have as the output would generally be the same. If you can easily tell the direction in which your subwoofer's sound is coming from your system either needs to be adjusted or upgraded.
Audio Formats
Monaural
Monaural (Mono or Phono) [1.0]
This is a 1 channel analog sound source. The full name is Monaural but it's often called Mono or Phono for short. Mono is obviously derived from Monaural but phono is derived from phonograph (a record player) which only has a single channel output.
Stereo
Stereo [2.0 or 2.1]
This is a 2 channel analog sound source. It is probably the most frequently used today. The sub-woofer channel (if used) is "created" by the decoding device as there is no data in the source material to identify what sounds should be sent to the sub-woofer.
Dolby Pro Logic
Dolby Pro Logic [3.0, 3.1, 4.0 or 4.1]
This is a 3 or 4 channel analog sound source. Dolby Pro Logic basically encodes the signals for front-center and rear within an analog stereo signal. A Pro Logic decoder then expands the stereo signal by looking at differences in the left and right speaker's signals to extrapolate what sounds should be coming out of the front-center and rear channels. If the receiving devices does not support Pro Logic decoding it will output only stereo sound. Despite the fact that it only has a single rear channel two speakers are typically used in the rear and their outputs are identical. Again, the sub-woofer channel (if used) is "created" by the decoding device as there is no data in the source material to identify what sounds should be sent to the sub-woofer.
Dolby Pro Logic II
Dolby Pro Logic II [5.0 or 5.1]
This is a 5 channel analog sound source. Dolby Pro Logic II uses the same idea as the encoding/decoding methods as the aforementioned Dolby Pro Logic with the exception that the rear channels are now independent.
Dolby Pro Logic IIx
Dolby Pro Logic IIx [7.0 or 7.1]
This is a 7 channel analog sound source. Dolby Pro Logic IIx uses the same idea as the encoding/decoding methods as the aforementioned Dolby Pro Logic with the exception that there is an extra set of independent rear channels bringing it to full 7.1
Dolby Digital 5.1
Dolby Digital 5.1 [5.1]
This is a 5 channel digital sound source. Unlike Dolby Pro Logic each of the 5 satellite channels as well as the sub-woofer channel are encoded independently and remain completely independent throughout the system.
DTS
DTS (Digital Theater System) [5.1]
This is a 5 channel digital sound source. Similar To Dolby Digital 5.1 each of the 5 satellite channels as well as the sub-woofer channel are encoded independently and remain completely independent throughout the system. DTS is considered a superior format to Dolby Digital because less compression is used.
Dolby Digital EX
Dolby Digital EX [6.1 or 7.1]
This is a 6 channel digital sound source. Similar to Dolby Digital This features the addition of a rear center channel. In some cases the rear-left and rear-right channels are moved forward to become center-left and center-right channels and the rear center is broken into two rear channels to make 7.1
DTS-ES
DTS-ES [6.1 or 7.1]
This is a 6 channel digital sound source. Similar to Dolby Digital EX.
DTS:Neo6
DTS:Neo6 [6.1 or 7.1]
This is a 6 channel analog sound source. Similar to DTS-ES and Dolby Digital EX in terms of speaker setup but similar in encoding/decoding to Dolby Pro Logic IIx.
Audio Cables
RCA Patch Cables
RCA stands for "Radio Corporation of America", as RCA is the company that set the standard for using this type of Patch Cable for connecting audio. RCA cables are the most common type of analog audio connection. One RCA patch cable is required for a mono signal. Two RCA patch cables are required for Stereo, and if encoding is used they can carry Dolby Pro Logic, Dolby Pro Logic II, Pro Logic IIx, and DTS:Neo6. In some instances where no particular multi channel encoding format is used (like in SACD and DVD-A devices) a single RCA patch cable might be used for each individual channel.
SCART
SCART Carries both Analog Audio As well as various video signal (see video section above). SCART cables have 2 way analog audio, meaning it can send and accept audio signals at the same time. SCART supports the same audio formats as RCA patch cables. SCART cables and connectors are only available in Europe and other PAL countries.
Digital Coaxial
Coaxial is the most common type of digital audio connection. It uses the S/PDIF (Sony/Phillips Digital Interface) standard to transfer the digital information. A Coaxial connection is essentially a single RCA patch cable that transfers all audio information digitally through a single cable. This format supports Mono, Stereo, Dolby Pro Logic, Dolby Pro Logic II, Dolby Pro Logic IIx, DTS:Neo6, Dolby Digital 5.1, DTS, Dolby Digital EX, and DTS-ES.
Optical Toslink
An Optical Toslink connection is very similar to Digital Coaxial in that it also uses to the S/PDIF format to transfer digital audio data except rather than using an RCA patch cable it uses a fiber-optic "Toslink" cable. This means that rather than the digital signal being transfered with electronic pulses through the cable. The signal is converted into pluses of light and then converted back into electronic pulses once it reaches it's destination. This format has the benefit of not being effected by outside interference between the source to the decoder, but a good quality Toslink connector can be very expensive. This format supports Mono, Stereo, Dolby Pro Logic, Dolby Pro Logic II, Dolby Pro Logic IIX, DTS:Neo6, Dolby Digital 5.1, DTS, Dolby Digital EX, and DTS-ES.
HDMI
HDMI is a single digital cable for Audio and Video (see video section above). This will most likely be the cable standard of choice for a while. For the audio portion of this cable it uses the same S/PDIF format as Optical and Coaxial. This format supports Mono, Stereo, Dolby Pro Logic, Dolby Pro Logic II, Dolby Pro Logic IIx, DTS:Neo6, Dolby Digital 5.1, DTS, Dolby Digital EX, and DTS-ES.
