What is Digital TV
A Complete Guide to Digital Terrestrial Television
DTV Transition, TV Reception, and DTV Troubleshooting
Do you know what Digital TV is all about, what are the advantages of DTV broadcast, and why the DTV transition has taken place?
DTV transition in the US has been over for almost three years now, yet many still feel confused about digital terrestrial television. What can you do to receive digital television broadcast? Can you still use your old analog TV? Why do you need to re-position or even replace your TV antenna?
Discover all you need to know about the latest and greatest TV change since the introduction of color TV—Digital Terrestrial Television, and see what you can do to receive free-to-air standard and high definition DTV services.
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Digital TV Basics: What is Digital Terrestrial Television?
Introduced in the 90s, digital television refers to an advanced broadcasting technology of images and sound by means of discrete signals (ones and zeros).
Also known as DTV, Digital TV is more flexible and efficient than analog television in that it has the potential to deliver higher-quality images and sound, more programming options, and new digital interactive services.
However Digital Television does not necessarily imply a better quality TV. The potential is there, but it all depends on the compression levels used by the television broadcasting stations in their aim to deliver more program channels over their allocated broadcast space, to outdo the competition.
This brings about a corresponding expense in image quality, depending on the level of compression used.
For the consumer, DTV refers to a TV set with a built-in ATSC tuner. ATSC stands for Advanced Television Systems Committee; this is the regulating body in the United States that governs digital TV standards. Worth taking note here that prior to the digital TV transition (completed in the US in June 2009), the Federal Communications Commission—the US government interstate communications regulating body, ruled that all new TVs sold after March 1, 2007 had to include a digital (ATSC) tuner.
Known as the 'digital tuner rule', this also mandated that TVs sold ex-stock after March 2007 without a digital tuner, had to include a 'Consumer Alert' to indicate clearly that the said TV would require a converter box to receive over-the-air broadcasts with an antenna after the DTV transition is complete.
Often, TV sets with an ATSC tuner are referred to as HDTVs in that all HDTVs are digital TVs. But care should be taken because as we will explain further on in this article, not all DTV sets are capable of displaying high definition content.
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The main reason for this change—also referred to as digital TV transition or DTV transition—is one of freeing valuable spectrum space. While the available spectrum has remained the same, available TV broadcasts and wireless services have increased to a point that urgent action became mandatory to manage properly this scare resource.
Digital television is more efficient in delivering TV content, meaning it requires less bandwidth due to compression techniques that are not possible with analog transmission. As a result, DTV can deliver more TV programs in significantly less spectrum space. Hence, it is possible to free up a good portion of the spectrum allocated for TV transmission, to use for other services.
But not only, digital television has the potential to deliver a clearer picture, and new interactive video and wireless data services that are not possible with traditional analog technology.
And there is another equally important reason for the DTV transition... MONEY!
New technology is always good for the economy, but not only. It is also good for the Federal Communications Commission; the FCC aim has always been to auction the freed spectrum space as a result of the DTV transition, expecting to raise some fifty billion dollars!
The digital television transition has nothing to do with cable or satellite TV. Digital terrestrial television services affect only TV sets hooked up to an over-the-air antenna. In other words, unless your TV has a digital TV tuner, you will not be able to receive DTV services; you would require a suitable converter box and an appropriate on-the-roof TV antenna.
While the misnomer is that DTV is HDTV, yet Digital TV comprises various TV formats and not just high definition TV. The most common are:
Standard Definition Television (SDTV): This is the basic level of quality and is the digital equivalent of analog NTSC. It comes in interlaced format and carries a picture resolution 640 pixels maximum by 480 lines in either traditional 4:3 aspect ratio or in widescreen 16:9 format.
Enhanced Definition TV (EDTV): This is the next level and represents a step-up from analog television and SDTV. As SDTV, it comes in either format, with the main difference between the two being that EDTV is a 480p progressive scan format only. This also means it has the same 480 lines of picture resolution but then supports a maximum of 852 pixels horizontally, the same as progressive-scan DVD players.
High Definition TV (HDTV): This represents the highest resolution and picture quality of all digital television broadcast formats. Unlike SDTV and EDTV, HDTV comes in various different formats, with the most common in the TV broadcast industry being 720p and 1080i, with only a few transmitting in 1080p.
Discussing the different HDTV formats is a topic on its own, yet one thing common between all HDTV formats is that these are only available only in 16:9 widescreen format. 720p carries a resolution of 1280 x 720 pixels in progressive scan mode while the 1080i interlaced format has a picture resolution of 1920 x 1080 pixels.
There is the misconception here that 1080i is better than 720p. This needs not necessarily be the case; for an understanding of this issue, please refer to our guide to HDTV Formats.
With the coming of digital TV, each broadcast channel still has an analog bandwidth of 6 MHz (8 MHz in most European countries), but then the measured capacity becomes digital. In this respect, each TV channel can carry a digital bitstream having a maximum data rate of up to 19.4 megabit-per-second or 2.4 megabytes-per-second. This is the bitstream required for full HD content.
The savings in bandwidth comes as DTV does not require the full 19.4 MBits/sec. It is all a matter of what the stations put in their allocated 19.4 Mbps bitstream. For example, a TV station may broadcast its HD at 15.5 Mbps or less, to simultaneously broadcast one or two SD channels, plus any other non-video datacasting services. How many channels a broadcaster fits in depends on the desired quality and compression levels.
At present, channels allocated for TV broadcast in North America, range from Channel 2 to 13 in the VHF (Bands 1 and 3), and Channels 14 to 36 and 38 to 69 in the UHF (Bands 4 and 5); channel 37 is considered a silent channel allocated for radio astronomy research and may not be used by any TV station.
However, what we have stated above implies that a DTV broadcaster does not need multiple broadcast channels to broadcast multiple program feeds at the same time. This means that not all of the originally allocated channels for analog TV broadcast are required for digital TV.
As a result, channels 52 through 69 have now been be reallocated for other purposes, thus freeing 108 MHz of valuable spectrum space thanks to the transition to digital television broadcasting.
More Content: We have already touched upon the main advantages of digital TV, namely reduced spectrum space, more content choice through multicasting, provide high-definition television services, and support of non-television services such as multimedia, interactivity, and program information.
The latter means that a digital TV receiver is able to display information about a show, or even call an electronic program guide (EPG grid). This is similar to cable or satellite TV boxes, listing upcoming shows arranged by channel, time of day, and day of the week.
Improved AV Quality: DTV supports 5.1 surround sound, and as expressed in the previous section, it also has the potential to deliver higher quality picture. In particular, from the digital TV reception aspect, the digital picture does not suffer from 'ghosting' and 'snow' affects so common with analog TV transmissions.
And what are the disadvantageous of digital TV?
The most obvious of all disadvantageous associated with digital television arise by way of the DTV transition process itself. The switching off from analog to digital meant that all non-digital televisions were made obsolete unless as further explained in the next section, use is made of an external digital tuner box. This is no big deal in that these boxes are relatively cheap, but having a set-top box renders your TV nothing more than a monitor; you would not be able to use your TV remote to change channels as this is handled by the converter box. And ending with two remotes is not the most convenient way to use your TV!
But there are a few others disadvantageous as well that are specific to digital TV...
Digital TV Picture Artifacts: Despite that DTV has the potential to deliver better images and sound than its analog counterpart, DTV images have some picture defects that are not present on analog television system. Artifacts such as quantization noise and blockiness are quite common in DTV pictures.
Quantization noise is the resulting error in the displayed picture signal between the actual 'analog' value and the discrete digital representation; this is inherent in any digital system. Blockiness arises when the picture breaks down when trying to display scenes with complexity. At times, a picture may also dissolve into a stuttering motion, or even a brief of total freeze when trying to display fast movement, or both.
This mainly happens with unconverted program content to be displayed in HD. But it can also happen with SDTV content as well and is the result of excessive compression levels used by the TV broadcaster to fit in the available content while reducing the required bandwidth. You see, digital TV is not a miracle technology - you get more content feeds from the same TV broadcaster thanks to compression techniques (MPEG-2) at the expense of a varying reduced quality.
Buffering: Another issue that may arise only with digital TV is what is referred to as preload delay till the set buffer enough content to begin showing the broadcast stream. This delay varies between different TV sets and leads to a significant delay in comparison to the almost instant response associated with an analog TV, when changing channels. This delay can make 'channel surfing' on digital television sets more difficult.
Effects of Poor Reception: While with analog television, it is still possible to display some form of degraded picture in difficult reception areas, with DTV reception, things are completely different.
In reality, this represents both an advantage and a disadvantage. An advantage because while with analog TV reception, you may experience a gradually degraded picture quality as reception conditions worsen, with digital television, you would still continue enjoying a perfect picture. However, this continues till the system reaches what is referred to as the 'digital cliff'. At that point, your DTV would not be able to generate a picture at all and would simply display nothing. In contrast, an analog TV would still continue to display some form of degraded image - no matter how worse it is.