[opendtv] Re: Which Modulation Would You Choose on a really bad day?
- From: John Willkie <johnwillkie@xxxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 25 Sep 2006 11:02:29 -0700 (GMT-07:00)
I beg to differ: I have repeatedly on this list defended the far-field
reception of 8-VSB. And, near-field is "getting better" (that's faint praise.)
John Willkie
-----Original Message-----
>From: "Stephen W. Long" <longsw@xxxxxxxxxxxxxx>
>Sent: Sep 24, 2006 7:21 AM
>To: opendtv@xxxxxxxxxxxxx
>Subject: [opendtv] Re: Which Modulation Would You Choose on a really bad day?
>
>Yes, the exact point. Digital is GREAT when it WORKS. This is why is it
>NOT (just) about signal strength. No one on this list has ever defended the
>native reception characteristics of 8VSB - it is and has always been a
>fragile modulation system. Since the whole point of the exercise is to
>receive pictures and sound, a system that digitally fades out because of
>multi-path echoes, is not a good choice for pictures and sound reception. A
>minor fade out may not affect some data types, if sufficient FEC is used,
>but MPEG-2 long GOPS appear to be very sensitive to these 8VSB signal drop
>outs - video freezes and audio drop outs do not make for a good TV viewing
>experience. I have had to just give up on watching ATSC signals in my
>house - the drop outs are just too damn annoying. Conversely, I can watch
>analog NTSC just fine. Low VHF sucks, but high VHF and UHF are received
>very well with my attic antenna, and I can get acceptable pictures using
>indoor antennas, even in the basement of my house.
>
>This "new" modulation discussion threat started when I bought a new 32" HDTV
>LCD TV for my home office. It delivers great pictures from my satellite
>HDTV service. I can receive exactly ONE 8VSB station with this new
>receiver. I have tried the attic antenna and one of the latest and greatest
>indoor antennas. There appears to be adequate signal strength (according to
>the signal strength meter in the set), but the pictures will not lock up -
>freeze and blocks and just crap.
>
>To add just a little more JP4 to the fire - one of the apparent reasons 8VSB
>was chosen was because of its theoretical high data rate. And just why was
>everyone so anxious about data rate - because of the very flawed assumption
>of the use of 1080/30i interlace HDTV. Interlace artifacts equate to noise
>which equate to poor coding efficiency, which means bits are wasted. If a
>more rational HDTV video format is chosen, such as 720/60p, better pictures,
>at a lower data rate are possible. The 720/60p pictures that ESPN releases
>when they do Monday night OTA football are STUNNING. The 1080/30i football
>pictures on another network are soft and full of motion artifacts. 1080i
>encoders are clearly throwing away the high frequency picture components to
>make the signal fit in the ATSC channel.
>
>ATSC is nothing but a collection of poor engineering choices and poor
>compromises. If 720/60p is your transmission video format, it would have
>been possible to select data rates below 14Mbps for DTV, which means a much
>more robust modulation system could have been chosen, to include DVB-T.
>When DVB-T parameters are chosen to match the ATSC data rate, it is still
>more robust than 8VSB.
>
>What is particularly illuminating to me at least as to the reason why COFDM
>was never seriously considered by the FCC engineering staff. Over drinks
>one evening an engineer told me COFDM was never considered because it would
>take them two to three years to re-compute the adjacent market interference
>and power allocations. When Sinclair started doing their public tests, the
>staff engineers would never consider a change to COFDM because the 8VSB
>decision that had already been made. It was never about COFDM not being a
>better choice, it was about it was too inconvenient to recalculate radiation
>patterns and interference.
>
>In the aftermath of the anticipated melt down when analog shuts down, during
>the hearings trying to find someone to blame, maybe some of the true reasons
>why poor decisions were made will come out. That is, if the documents have
>not all been shredded by then.
>
>Meanwhile, I will continue to have to pay a vendor to deliver digital OTA
>television signals to my house via fiber or satellite. A suspicious person
>might begin to think this was the objective all along.
>
>Stephen
>
>
>
>-----Original Message-----
>From: opendtv-bounce@xxxxxxxxxxxxx
>[mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of negrjp
>Sent: Sunday, September 24, 2006 5:46 AM
>To: opendtv
>Subject: [opendtv] Re: Which Modulation Would You Choose on a really bad
>day?
>
>
>Dear Friends,
>
>COFDM X VSB controversy started in the same time of the creation of these
>systems.
>
>
>In 2000 Brazil it made RF covering tests with American 6 MHz ATSC's 8VSB,
>European 8 MHz COFDM's DVB and 6 Japanese MHz COFDM's ISDB-T in Sao Paulo
>megalopolis,using broadcast transmitters in the highest tower of the city.
>
>The Japanese system was considered best. However, this version 6MHz COFDM
>failed in 8% of the analyzed localities. Brazilian Scientists are testing a
>"solution" to solve this problem with broadcasting diversity.
>
>When I are little boy, somebody was said that the SSB would be the system of
>communication of the future. Nobody said in digital communications systems,
>however CW is digital...
>
>It will be that the true controversy is digital x analog?
>
>TTFN,
>
>Jonas
>from Brazil
>
>
>
>> Ian Mackenzie wrote:
>>
>> >As you well know because of border issues Mexico and Canada
>> >had no choice in selecting a DTV modulation method.
>>
>> I don't understand why this should be the case. Especially if Canada and
>> Mexico had opted for a 6 MHz version of DVB-T, in which case the situation
>> would be much as it is in Europe between PAL and SECAM countries with
>common
>> borders.
>>
>> >Any settop HD in Australia will work in any other DVB country in
>> >HD and SD. (They have an SD downconverted output as well as
>> >the HD outputs) This is what is called a STANDARD.
>>
>> Do the Aussie STBs support H.264 HDTV? If not, they won't work in the only
>> other DVB-T HDTV country, which is France. As to SD outputs, that's true
>for
>> all ATSC STBs as well. They *all* have composite and S-video outputs, as
>far
>> as I have seen, in addition to the various analog and digital HD outputs.
>>
>> But all of this is much ado about nothing. I showed that Philips,
>> STMicroelectronics, and Micronas (at least those) already have global
>> standard reference designs, and that at least one manufacturer in the UK
>> already *sells* two models of global standard DTT integrated receivers,
>for
>> what seems to be competitive prices. Why all the fuss? Who cares? If DTT
>> STBs don't sell well in the US, it is caused primarily by three factors:
>(1)
>> the vast majority prefer cable and DBS, (2) most TV sets now come with
>> built-in ATSC anyway, (3) broadcasters have made it so procrastinators can
>> be perfectly happy continuing to use NTSC. Probably because they're afraid
>> of cable or DBS backlash if they worked to make their DTT offerings more
>> fun.
>>
>> >The big joke is that DBS worldwide uses DVB including the USA
>> >systems. OK not COFDM but the DVB-S system used is all part of
>> >the integrated DVB solution of DVB-T, DVB-S, DVB-C and DVB-H.
>>
>> I still think this is much ado about nothing. The only significant
>> difference between ATSC and DVB-T that creates all the pointless yelling
>is
>> the physical layer -- 8-VSB vs COFDM. Take that away, and the rest is just
>> the sort of obtuse silliness that broadcast standards around the world
>have
>> always created. Whether it was different versions of NTSC, PAL, and SECAM
>> around the world, the industry has obviously cherished its quite
>deliberate
>> incompatibilities.
>>
>> Bert
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