Saturday, March 29, 2014

High quality HD over standard antenna??




Nic W


Today, on the radio, I heard that HDTV of standard channels (ABS, CBS, NBC, FOX, PBS) is broadcast free of charge over standard "Old fashioned" TV antennas.

This reputable radio host also mentioned that this form of HD was actually BETTER than cable or satellite because it was not compressed format.

Anyone know anything about this? Also, is there a way of taking advantage of this broadcasting without the "Roof mounted" antenna? Like maybe rabbit ears or something?



Answer
Yes, it's true.

DTV (including HDTV) is already broadcast in most of the US.

And DTV uses the same antennas as the old analog system. Some people will need better antennas though; DTV can be fussy about signal quality. If you already get good analog TV reception, your current antenna is probably good enough.


You can use any old TV with a cheap converter box to receive HDTV signals, but you will only see a DVD quality picture because that's the best that analog TVs were built to display.

To see HDTV broadcasts in "HD" resolution, you need one of the following:

A HDTV (includes ATSC tuner)

A "HD ready" TV and an external ATSC tuner box

A computer equipped with a SVGA or better display and a ATSC tuner card or USB tuner.

Is over-the-air HDTV signal better than cable or satellilte?




Uncle Penn


I was listening to a popular radio consumer advocate. He said that you will actually get a better picture using an antenna to get your HDTV vs. cable or satellite. The reason given was that cable and satellite have to compress the signal, but free over-the-air does not.

In the computer world, there's lossy compression, like JPEG, where some clarity is lost. Then there's ZIP where no data is lost and you receive a perfect reproduction.

So I guess their are 3 questions:

1. Is an over-the-air signal compressed or not?
2. Do cable and sattellite companies use a "lossy" compression scheme for the HDTV signals.
3. Is it true that the HDTV picture is superior if received from over-the-air transmission.
To Pancakes - HDTV has resolutions of 1080i and 720p, both superior to progressive DVD which is 480p.



Answer
The ATSC standard for HDTV transmission is MPEG-2 compression and 19mbit data rate. OTA and cable both use MPEG-2, as does most satellite transmission. Some recent satellite local stations are compressed with MPEG-4. All HDTV is compressed. However, the MPEG specs allow for different amounts of compression and different qualities. When OTA utilizes the full bandwidth for a single HDTV channel at 19mbs, you will get the best quality obtainable from HDTV. However, many OTA stations will broadcast several programs on sub-channels simultaneously with their HD channel. That steals bandwidth and bitrate from their HD channel, and if that is done too much, the HD picture quality will suffer (the subchannels are usually not HD). So you cannot lump all OTA into one category for picture quality.

The same is true for cable channels; they have the option of retransmitting the exact signal broadcast, in which case the cable will have the same quality as the broadcast. However, some cable systems will decompress and recompress the signal so they can use a lower bitrate and less bandwidth. If they do that, the cable's picture will be poorer than OTA. It is also possible for the cable to receive a higher-quality signal from the station (less strongly compressed) that the networks use to distribute their HD content. If the cable system then compresses that signal to a high bitrate, but the broadcaster limits its bandwidth, the cable signal would be better. i do not know if this latter approach is being used by any cable companies at this time, but it is a possibility.

Finally, satellite compression is often more severe than OTA or cable, and my experience with satellite HD is that for the major networks, it is not as good as OTA or cable. However, special HD channels on satellite (HDnet, Discovery HD) are excellent.

In summary, the answer to our question is: it depends.

Finally, all MPEG compression schemes are "lossy". It would be impossible to get the HD picture in the allotted bandwidth with lossless compression. But the degree of "loss" is flexible and up to the party doing the enccoding.




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