AVS Forum banner
Status
Not open for further replies.
1 - 10 of 10 Posts

·
Registered
Joined
·
173 Posts
Discussion Starter · #1 ·
The Chief at a local station has published a breakdown for their 19.39Mbps channel:


12Mbps for 720p HD

5Mbps for 480i SD

2.39Mbps for "other things"


My question is, will 12Mbps provide maximum HDTV resolution?


[This message has been edited by Rayman Carlton (edited 04-06-2001).]
 

·
Registered
Joined
·
1,386 Posts
Hi, Rayman,


HDTV's bitrate requirement is variable depending on scene content complexity. For example, a still image of some simple artwork and lettering would require very few bits to transmit but, at the other extreme, a basketball game with lots of fine detail and rapid motion would eat up quite a lot, perhaps up to the maximum available in the ATSC system at times. Most of the time 12 Mbps will be pretty decent looking. I'd worry about how a "b-ball" game might look though. I believe that stations like WRAL-DT in Raleigh that have some experience with simulcasting HD, SD and data tend to assign about 12 Mbps for HD most of the time and then dial-in more bitrate to accomodate the higher payload capacity needed when artifact-free performance on live sports programs in HD is desired.


------------------

HiDefDave


STOP HDCP!


[This message has been edited by Dave McRoy (edited 04-06-2001).]
 

·
Registered
Joined
·
1,125 Posts
Question about bandwidth for HD (not bit rate), what is the min max for a switcher to pass the signal without degradation. I have been told that 150 mhz is all you need. Then I've been told that you need at least 300 mhz for a HD signal. So, what is needed to pass the HD signal without degradation.

John
 

·
Registered
Joined
·
1,386 Posts
John,


If HDTV were to be transmitted over-the-air, uncompressed in analog form, the breakdown would be as follows:


NTSC 480i/30: 4.42 MHz (in a 6 MHz channel)


ATSC 720p/60: 33 MHz


ATSC 1080i/30: 33 MHz


Since maintaining 6 MHz channel allocations was desired, it was decided that digital, compressed signals would be used. ATSC includes lossless and "lossy" compression, in which some picture information deemed to be unimportant is eliminated in order to transmit the data required to recover an HDTV picture within only 6 MHz.


Regarding bandwidth required to switch uncompressed HD video, 100 MHz seems to be a common specification for professional HDTV switchers, routers, etc. When you seen a consumer HD switching device touting 350 MHz or some such it's usually either a case of the device needing to pass 350 MHz with minimal attenuation in order for the phase response down near where the video signal is to be adequate or perhaps just a case of "guilding the lily." But no high-end consumer electronics manufacturer would ever do that. http://www.avsforum.com/ubb/wink.gif



------------------

HiDefDave


STOP HDCP!




[This message has been edited by Dave McRoy (edited 04-06-2001).]
 

·
Registered
Joined
·
730 Posts
Quote:
Originally posted by wanthdtv:
This makes me wonder had HD been originally broadcasted in analog format

instead of the digital format, would HD actually had looked better since there is very little compression associated with analog.

In other words you will not have to deal with the sometimes distracting artifacts often associated with MPEG coding.
Well, your question seems to be "Does HD without lossy compression look better than HD with lossy compression?" Of course the answer is yes, but that is not much of a question is it?


The goal of the FCC is to use RF bandwidth as efficiently as possible and broadcasting analog HDTV would have been a very *very* poor decision in light of inexpensive computing power.

Quote:
Originally posted by wanthdtv:
Keep in mind that this was how Japan originally aired HDTV. Yes I know it was PAL not NTSC but it was still analog in nature.
Japan is actually an NTSC country, but neither NTSC nor PAL are terms used when talking about HDTV. You might want to do a bit more background reading.

 

·
Registered
Joined
·
196 Posts
Analog channel bandwidth is a function of the total number of pixels and the horizontal picture scan rate. It would be difficult to transmit analog HDTV in anything less than about a 30 MHz channel.


Even line-doubled video (480p DVD or VGA graphics) requires about 10 Mhz of bandwidth.


The nominal data rate for ATSC HDTV in a 6 MHz bandwidth is 19.39 Mb/s. Tests have been done allocating 15 Mb/s for 720p/60 and the balance for 480i. PBS allocates 4.5 Mb/s for four SDTV multicast channels, with the remainder for data.


Tests have been done combining one 1080i channel and two SDTV channels, but there is noticeable degradation with motion images.


Uncompressed 720p/60 is about 858 MB/s, and uncompressed 1080i is around 930 Mb/s - not a lot of difference, once they are compressed to 19.39 Mb/s.


If I am not mistaken, the HDTV analog system in Japan - MUSE - was a satellite system with greater available bandwidth.


Hope this answers your questions.


KC
 

·
Registered
LG 55" C9 OLED, Yamaha RX-A660, Monoprice 5.1.2 Speakers, WMC HTPC, TiVo Bolt, X1
Joined
·
45,617 Posts
The older analog HDTV system developed in Japan was called MUSE. Sony Hi-Vision had a full line of cameras, recorders, monitors, etc. Although I don't remember it's bandwidth, I would guess it would have to be higher than 33 MHz. The big difference compared to the ATSC system is the digital artifacts. MUSE being analog had none and ATSC, for example the high motion NCAA games last weekend, has easily see-able pixelization.


Both systems have interlace artifacts, with MUSE being 1125i and the MUSE system was also subject to typical analog video artifacts like video noise and color shift. It was my first exposure to HDTV and back in 1989 I was mightily impressed.


------------------

"better living thru modern expensive electronics"

tm
 

·
Registered
Joined
·
868 Posts
All this talk about analog bandwidth is meaningless without specifying how many dB down the response is at the bandwidth specified. Professional broadcast equipment normally specifies bandwidth as the upper limit to which the frequency response is flat within plus or minus at most a few tenths of a dB. Also the group delay variation needs to be fairly small over the operating bandwidth.


To pass uncompressed analog HDTV requires three channels the required bandwidth required for the channels will depend on whether you are talking about RGB or Y,Pb,Pr. If it is RGB three identical channels with a flat response bandwidth of a bit over 30 MHz is required. If it is Y,Pb,Pr then one 30 Mhz and two 15 Mhz analog channels are required. Again the channels need to have a response flat within a few tenths of a dB to the upper limit and a slow response roll off above the limit to provide minimum group delay variation within the video band.


These values will pass analog HDTV essentially transparently. For consumer applications more roll off can be tolerated before the picture starts to become visibly soft. You need to rememberer that specifications for professional equipment are held tight because the video may pass through several pieces of equipment and the loss for any one thing must be held small to make the final result still look good.


The data rate for uncompressed HDTV is 1.5 giga bits/second for 1080I/30 or 720P/60. The data rate for uncompressed component 480I/30 is 270 mega bits/second.




------------------

Rory
 

·
Registered
Joined
·
235 Posts
This makes me wonder had HD been originally broadcasted in analog format

instead of the digital format, would HD actually had looked better since there is very little compression associated with analog.

In other words you will not have to deal with the sometimes distracting artifacts often associated with MPEG coding.


Keep in mind that this was how Japan originally aired HDTV. Yes I know it was PAL not NTSC but it was still analog in nature.


If someone has seen HDTV in both formats could you please give your opinion on which you thought presented a clearer picture.
 
1 - 10 of 10 Posts
Status
Not open for further replies.
Top