Question about QAM, ATSC, and Digital

[thetmaxx]

I've been pretty happy with my regular old analog tunning GBPVR machine. it works with no problems to speak of. but I have been reading a lot about QAM, ATSC, and digital stuff. I have a HVR-1600 and always wondered what goes to it's digital side? and what do these terms mean.

my service is basic cable, and comes in @480. I know my provider offers digital, but nothing that says HD. is digital/qam/atsc automatically HD or can it be 480 as well?
also do the antennas marked for digital over the air hdtv ready, do they tune 720 right over the air? (I'm surrounded by local tv towers) and is this antenna only for my digital tuner?

Sorry if these questions are basic, I've been reading through the forums a lot, and just can't get a grasp on what you guys are talking about. Especially qam, that seems the most complicated...

[johnsonx42]

my service is basic cable, and comes in @480. I know my provider offers digital, but nothing that says HD. is digital/qam/atsc automatically HD or can it be 480 as well?

It may be either one; for me on ATSC (in california), most channels have 1 HD 720p or 1080i feed, and then some channels also have additional sub-channels that are almost always 480i. There is theoretically enough bandwidth on 1 digital ATSC channel to do 2 720p feeds, but I've not seen it done myself.

On ClearQAM, if your cable company actually provides it, you may get a dozen different feeds (channels) on a single QAM channel (or frequency); this makes QB-PVR's new Multi-Record function quite useful as you can then simultaneously record any or all the feeds on a single channel using just one tuner. Again though, QAM doesn't mean HD, it just means digital - the channels can be 480i, 720p or 1080i.

Broadcasters are free to over-compress their digital feeds and give you a crappy picture if they want to, or they can keep the bit-rate up and make even a 480i picture look like HD. I'm often surprised at the quality of the SD feed on KNBC 4.2 Universal Sports, more than once I've pulled up an info screen wondering if they hadn't switched over to HD during the night...

also do the antennas marked for digital over the air hdtv ready, do they tune 720 right over the air? (I'm surrounded by local tv towers) and is this antenna only for my digital tuner?

The whole 'HDTV' antenna thing is a bit of marketing hype... HDTV is/will be broadcast on all the same frequencies that existing analog TV is, so as a general rule you need the same sort of antenna. Currently all of the digital broadcasts are in the UHF range, as there are no free VHF channels available until analog goes dark in February. On Feb 17th, many (but not all) digital channels will move back down to their stations' traditional broadcast frequency - for example, KABC7-DT is on UHF 53 now, but will move down to VHF 7 as soon as KABC7 Analog shuts down (convenient for me - one of my tuners seems to have lost the ability to tune UHF 53).

HOWEVER, at least from what I can see in So Cal, they're not going to use the VHF LO channels (2-6), since those are the hardest to receive (I presume). KCBS 2, KNBC 4 and KTLA 5 will all stay on UHF channels after the switchover. Due to the relationship between KCBS and KCAL, KCAL will move back down to VHF 9, and KCBS will take the UHF frequency being used now by KCAL DT.

UHF channels 52-69 are going away on Feb 17th; those are the ones whose spectrum was auctioned off a bit ago. KCBS's temporary digital frequency is in this range, as is KABC's and many of the other networks.

This means that all us ATSC users will have to re-do our channel scans in GB-PVR on Feb 17th. I don't know if regular HDTV's will get some sort of signal that tells them to re-assign the channels, or if they'll have to re-scan too.

If you haven't noticed yet, all digital channels are numbered virtually - their channel 'number' no longer has any relationship to their broadcast frequency. So even now, KABC DT is channel 7, even though it's on UHF 53, and KNBC DT is now, and will be, channel 4, even though they aren't and won't be using VHF 4 any longer.

[whurlston]

That has to be the absolute clearest explanation of the Analog/Digital channels and the Analog->Digital conversion I've ever read. Well done.

[dennit]

That has to be the absolute clearest explanation of the Analog/Digital channels and the Analog->Digital conversion I've ever read. Well done.

That was a great explanation, but one part may not have come through clearly. Most cable providers currently supply both analog and digital on the same cable. The digital is quadrature amplitude modulated (QAM) and typically includes both encrypted and unencrypted ("clear QAM") signals. The clear QAM is required by law in the U.S. for your local stations, but cable companies don't bother to tell you this. They fear you may buy the less expensive analog cable then watch your locals in HD.

The term QAM refers to the modulation technique for digital cable. The term 8VSB refers to the 8-level vestigial sideband modulation technique for Over the Air OTA broadcast signals in the U.S.. Both modulation techniques bring you digital data which arrives in the ATSC standard format. ATSC is the digital TV format adopted in the U.S. For some reason, people refer to QAM (the modulation technique) when discussing digital cable, and ATSC (instead of 8VSB) when discussing broadcast TV.

What all this means is that if you subscribe to analog cable, you get digital HD cable for free for the local channels. Since you have a HVR-1600 and subscribe to analog cable, you can just put a splitter into your line and feed the second output to your ATSC input on the 1600. Set up a source for QAM and scan. You should get HD without any further hardware, depending on what your cable supplier offers. Try this link to see what is offered QAM cable or 8VSB broadcast in your area.

Side note: the 1600 is very picky about signal strength for QAM - I would feed your ATSC input on the 1600 card without any splitters when doing the scans and use the signal strength monitor app from Hauppauge. You want a signal strength over 30.

[htewam]

A very good explanation that I could have used about three weeks ago when I started my move over to digital :-) I pretty much used the approach outlined by dennit above - cable splitter into both inputs of my HVR-1600 -- luckily I had no problems with signal strength. As a novice, I have found it much more slow-going with moving to Clear QAM versus analog.

As a cautionary tale for thetmaxx: some of the issues that I ran in to (and have slowly been resolving) include:

a) My initial gbpvr channel scan found 70+ digital subchannels -- but only about 20 were "real"... figuring out which ones mapped to which EPG channels took me days -- mostly due to false starts.

b) I found that the Silicondust hdhomerun listing (as shown in dennit's link above) was woefully incorrect for my zipcode and I had trouble mapping the entries they listed to what was reported during the gbpvr configuring process. In the end, I mostly just had to compare against the analog channel line-up using my TV.

c) I found that the digital broadcasts required a couple of filters/decoders that I never previously had installed -- and never needed for analog -- this included an AC3 audio decoder and the resulting .TS files would not play back on my default Windows Media Player installation without the addition of some new plugins. My gut feeling is that all of this experimentation has added tremendously to the bloat-ware on my machine but I'm too fearful of breaking something to remove any of the extraneous mux/filter combos that I tried but failed with.

d) I use several MediaMVP boxes scattered around the house to view the Gbpvr recordings -- but this opened up the whole mysterious world of transcoding since the MediaMVP is very restrictive about the data it accepts. I've only just begun to make headway in this area and still have a way to go.

So... I've had some success but it certainly has been eye opening related to the complexities of changing over from "just plain analog" to "the wonders of digital"... and since I'm currently bound to my MediaMVP implementations, I can't really take advantage of digital HD at the moment.

[TonyXL]

I've been going the QAM route as well, here are some things that helped me:

1. Search some of the other message boards out there to get your local QAM mappings. I found mine on the dslreports and sagetv message boards. The Sage board actually has a dedicated QAM mapping thread. Saved me hours since my scan picked up hundreds of (mostly encrypted) QAM channels.

2. Try different muxes. TS is currently working best for me, especially with the sub's latest TS reader (http://forums.gbpvr.com/showpost.php?p=3...stcount=35). Comskip and srt captions are still a bit off, though. On the plus side, the multirecord is working well, and all of my major networks are on the same QAM channel.

DVR-MS gives me perfect comskip and caption timing, but often freezes up during recording. Still trying to diagnose this. I'm going to try the ATI and Cyberlink ones next (http://forums.gbpvr.com/showpost.php?p=3...stcount=60).

[thetmaxx]

Thank you guys so much for the info. I was just dissapointed tonight. I connected it to my cable, selected QAM and did a search. got about a dozen channels all said and done. I tried to preview them with nothing, just black. So I tried a few other channels, then one frame of very clear video popped up, and the whole GB-PVR config froze up!

So I tried again, most of the signal strengths said -6000 and quality was around 90. So I was clicking through them getting black screen, then one of them made sound. no vid, and gb-pvr froze.

So I decided to try ASTC, dug out my old 1980's rabbit ears and sure enough picked up most my locals with signal strength at -7000 and quality of 90-100. So I tried one of the local HD's and it come up and was playing with a very good picture. I watched it for a second, then changed to another channel and all of gbpvr config froze once again!!!!!!!!!!! how frustrating!!

anyone know whats happening?

also I don't want to mess up my EPG xml thingy, how do I tie these channels into GB-PVR? does it work as a seperate channel in the TVguide? (will it have a PBS for ATSC, and a PBS for my cable input? )

Anyways, Some help would be great!! It's just so cool, but something isn't working right...

[whurlston]

Don't worry too much about the freezing. It it common with QAM. It's annoying but the Config displays the channels a little differently than the actual PVRx2 application. Sub has stated that he has plans to revamp the config channel mapping process and also plans to look into the freezing issue.

Once you identify a channel, all you have to do is select it in the list of EPG channels on the left. This will expose a dropdown of the channels listed on the right, just select the one you want. Once you have them all mapped, save and exit.

[thetmaxx]

OK, I got it to work for the ATSC channels I found. It's so sweet actually watching TV in HD. I was watching the locals while recording from my cable, so sweet! I'm thinking of trying the QAM again, and not trying to preview the channels because they all come up unknown (my oTA ones came up with names so it was easy) thinking of trial and error testing them on certain channels, then writing down what comes up as what, and doing it that way. Cuz while the rabbit ears are sweet there are still some reception issues with certain channels. Still blows me away my 1980's rabbit ears tunning HD, can't wait to set this up on my parents new digital TV, since they still refuse cable...

Thanks again you guys for getting me going, all this just makes GBPVR that much more worth all the problems i've hurdled in that past.