Q: I have excellent reception of all of the local digitals -- most of the time. But occasionally one of the stations will be lost for 30 or 40 seconds, breaking up and then coming back with a very strong signal.
Why does this happen, and what can be done to eliminate the problem?
A: This sounds like a case of multipath interference.
Multipath is just what it sounds like -- the signal from one or more stations is arriving at your antenna from multiple paths, most likely as a result of it bouncing or reflecting off some topographical or man-made object as it travels between the the station transmitter to your home. In the analog world, multipath resulted in out-of-sync, multiple images on screen that were often referred to as ghosts; in the digital world, the second signal causes the receiver to null out the signal until it can lock on a single signal. This explains why you intermittently receive picture/sound and then nothing.
Multipath can be fiendishly difficult to eliminate, but antenna placement can help. If you can, move your antenna a few feet left or right, up or down, or play with angle of orientation. The goal in repositioning is to try to find a spot where the antenna will not see the secondary signal that is causing the multipath.
Over time the digital receivers have become more adept at rejecting multipath signals, with each generation doing slightly better in this regard than the last. If you're using an older receiver, an upgraded, more current receiver may help, but there's no guarantee that would cure your problem.
Also, a directional antenna (like a yagi attic/roof antenna) will perform better in installations where multipath problems occur. Multi-direction antennas are better at pulling in more stations without adjustments, but they sometimes increase the incidence of multipath issues.Q: Sometimes the pictures on my local digital stations are fantastic, but a lot of the time they don't look that much better than what I was receiving over cable or satellite previously.
Why? Is there something wrong with my television or OTA receiver?
A: At this point in the transition to digital HDTV, local stations are only providing a small portion of their daily broadcast schedule in the HD format. In almost all cases, the only HD programming available is when the local station's national network affiliate provides a program in the HD format, and the local station passes it on via its digital channel.
As a result, HD broadcasts are largely limited to prime-time programming, with the main exception being certain sporting events that are broadcast live in HD, such as selected NFL games, the Olympics, some college basketball games, some golf tournaments, etc.
Whenever a local station isn't receiving and passing on an HDTV network broadcast, they simulcast and "upconvert" their local programming on the digital channel. You probably understand the concept of simulcasting, but "upconverting" may require some explanation.
In order to simplify this, let's take the example of local channel KSDK-DT. Whenever KSDK-DT is sending an HDTV program, they send it in the 1080i HD format. Likewise, when they transmit a "standard definition" program, they are also sending it in the 1080i format by taking the original NTSC (480i) signal and electronically converting it to the same 1080i format used for HD.
The important thing to understand is that "upconverting" is not a magical process of transforming a sow's ear (NTSC programming) into a silk purse (HDTV). The limiting factor is the resolution of the original picture. If the original source material was created in the 480i format, there's no way to create HD resolution out of thin air.
This is similar to trying to convert a Polaroid snapshot into a professional studio portrait. There's no question that the professional photographer or film processor could make the Polaroid snapshot larger or produce it on nicer stock, but the end results are never going to be confused with a picture that originated as a studio portrait using higher-resolution film and equipment.
As in the case of NTSC programming, the limiting factor is the original resolution when the image was captured.Q: Why can't I change the screen mode for my television on the OTA digital channels?
A: Digital broadcasts (for the most part) are required to send their images out as a widescreen (16x9) picture. Although it's not always obvious from looking at the images, where black bars appear on the sides, these are actually formatted as part of the picture sent by the station.
One other point about digital broadcasts and your HD monitor. Many consumer televisions assume that when they receive an HD signal that the picture is being sent in widescreen format. In some cases this will limit or (more commonly) completely prevent the viewer from changing how the picture is formated onscreen. While the screen mode or aspect ratio controls for your set can be used with standard-definition programming, they may be non-functional or limited when your set is displaying either upconverted SD or true HD OTA broadcasts.Q: I understand that HDTV supports the Dolby Digital 5.1 surround sound format, but this doesn't appear to be working on my sound system. Is there a problem with my OTA receiver or my A/V receiver.
A: It's true that Dolby Digital 5.1 is part of the ATSC specification for HDTV broadcasting. However, there are a few conditions that need to be considered before determining what you're receiving and whether there's a problem with your equipment.
1. You need to have in place equipment capable of receiving and processing DD5.1 broadcasts (a DD5.1-compliant A/V receiver or processor) and you need to be using a digital audio connection between your OTA receiver and A/V receiver or sound processor. There are basically two types of digital audio connections, one that makes use of coaxial cables and the other using optical cables.
You will need to consult the user manuals for your OTA receiver and audio equipment to ensure that you are making the correct connections for your particular equipment and configuration.
2. DD5.1 broadcasts require special equipment to be installed at the local station. Although you may know that a specific program is being sent by the network in the DD5.1 format, if the local station here isn't able to process and decode the DD5.1 soundtrack, you won't be able to hear the DD5.1 mix in your home theater.
Here's a list of the stations in St. Louis and their ability to send Dolby Digital 5.1:
26 (11-2) -- KPLR (WB) - yes
31 (30-1) -- KDNL (ABC) - yes
35 (5-1) -- KSDK (NBC) - yes
39 (9-1) -- KETC (PBS) - no
43 (2-1) -- KTVI (FOX) - yes
47 (46-1) -- WRBU (UPN) - no
56 (4-1) -- KMOV (CBS) - yes
Also, here is the Dolby Digital 5.1 status of some of the major cable/satellite HD stations:
HBO-HD -- yes
ESPN-HD -- no
BRAVO-HD -- yes
Discovery HD Theater -- yes
HDNet Movies -- yes
HDNet -- yes
TNT-HD -- no
NBC-HD East/West -- yes *
CBS-HD East/West -- yes *
FOX-HD East/West -- yes **
* = only available to St. Louis viewers who obtain a written waiver from the local affiliate
** = the East Coast FOX out-of-market feed is now available to all St. Louis-area DirecTV HD subscribers who are paying for the local channels package. No waiver will be required for receipt of the the East Coast FOX feed, as KTVI, the local FOX affilliate, is directly owned by FOX television. (updated 1/2005).
3. Not all programs are available in the Dolby Digital 5.1 format, so even where one of the stations listed above is shown to be capable of transmitting DD5.1 broadcasts, if the program isn't created with a DD5.1 soundtrack, the local station won't be able to send in that format.
As an example, although KMOV-DT is capable of providing Dolby Digital 5.1 sound, "Everybody Loves Raymond" is not produced with a DD5.1 soundtrack. On the other hand, although "NYPD Blue" is produced with a DD5.1 soundtrack, local station KDNL-DT isn't currently equipped to handle DD5.1 broadcasting.
I've yet to find a completely reliable source of information about HD programming that includes a DD5.1 soundtrack, but HDTV Magazine Program Guide is the best that I've found so far:http://www.hdtvmagazine.com/programming/guide.php
In order to customize the guide for the local and/or cable/satellite channels you receive, it will be necessary to register with HDTV Magazine and set up a profile listing your stations. Note that the DD5.1 designations in the HDTV Magazine grid are "program-specific" and therefore won't accurately reflect the ability of the local station to provide DD5.1.Q: I'm not clear on the difference between "true HD" and "upconverted HD." Take for example the "Hogan's Heroes" re-runs that sometimes are shown on HDNet -- how can a show that wasn't originally recorded in HD be considered real HD?
A: I think your skepticism about "true HD" comes from a misunderstanding of the difference between "upconversions" and true HD programming. The "Hogan's Heroes" example you mention is a good way to illustrate the distinction.
Let's pretend for a moment that one of our local St. Louis stations holds the local syndication rights to "Hogan's Heroes" re-runs and that these programs are based on the same film-to-NTSC video transfers that appeared when the series was a first-run sitcom on CBS a couple of decades back.
When the local station shows "Hogan Heroes" reruns, the picture quality over the station's analog channel will be largely the same as any other NTSC prime-time drama or comedy series. However, when the show is transmitted on the local station's digital channel, it will be electronically upconverted to either 1080i or 720p, depending on which HD standard this particular station normally uses.
Note the words "electronically converted," because what happens when the program appears on the digital channel is that the 480 lines of NTSC video resolution are "reconstituted" to match the station's 720- or 1080-line digital broadcast. The important thing to understand in the hypothetical example here is that even though "Hogan's Heroes" is being converted to 720p or 1080i broadcast formats, the underlying video is still only 480 lines of resolution -- an electronic conversion can't create resolution beyond what existed in the original video frames.
On the other hand, what HDNet has done is to go back to the original film masters of the "Hogan's Heroes" series and performed a true "HD transfer" of those film frames to 1080i HD.
At the risk of oversimplifying the process, HDNet has "re-scanned" the film master in order to capture more of the resolution that existed in the original film frames of the series but that was lost when the film was converted to 480-line NTSC video. At the same time, HDNet has exposed more of the original film frame in order to fill (or nearly fill) the 16x9 aspect ratio mandated in the HD standard.
One other point that may be muddying the waters for you is the dfference between HD that originates via film (most theatrical-release films and most prime-time TV dramas or sitcoms) and HD that originates as true HD video (live sports, concerts, etc).
In general, HD that originates as HD video may have clearer and more lifelike quality to it, but in fact, 35mm or 70mm film contains as much (actually more) inherent resolution as the highest ATSC HD video standard (1080p x 1920). While they do appear different and you may think HD native video looks better, when a film-to-HD transfer is done properly, it qualifies as "true HD."