Thursday, December 20, 2007


What an HDTV PC Tuner does (and what it doesn't do)

An HDTV PC Tuner does one thing, it receives digital MPEG-2 encoded packets from an over-the air or cable broadcast and passes them to a HDTV tuner software application. If a packet is not received correctly for whatever reason, that data is lost. Digital/HDTV is a “get it all or get nothing” proposition, as opposed to analog broadcasts where weak signals can be captured and displayed on a TV, with the result usually being a snowy picture.

The difference in HDTV tuners boils down to:

  1. Whether they can tune cable QAM
  2. PC processor utilization
  3. How well they pull in weak and multi-path signals.
  4. Cost
A multi-path signal is a broadcast signal that has been reflected by trees, buildings or other objects to the tuner. In the analog TV world it translates to “ghosts” on the screen. With HDTV, multi-path can confuse the capture process, resulting in corrupt data, which in turn means lost data frames ultimately resulting in a flicker or jerky picture. The better tuners have the ability to lock in on the strongest signal and disregard the weak multi-path signal(s), and to pull in the weak broadcast signals. If you are in an area with lots of obstacles, a tuner with good multi-path filtering such as the Vbox Cat’s Eye 150 or one of the Fusion 5 tuners is recommended.

The quality of a HDTV picture depends on several things. Those under your control are: the MPEG-2 decoders*, the graphic card*, and the HDTV monitor. Since the HDTV tuner only captures and forwards data, it is not on the list.

If the decoders, graphics card and monitor stay the same, the digital/HDTV picture displayed will look same regardless which HDTV tuner and tuner software is used.

This assumes that the broadcast signal is strong enough for each tuner and multi-path does not cause packet loss.

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