|
|
 
|
|
Author
|
Topic: DVI vs. BNC 5
|
|
|
|
|
Robert Minichino
Master Film Handler
Posts: 350
From: Haskell, NJ, USA
Registered: Dec 2005
|
posted 05-31-2007 06:08 PM
BNC5 is a form of component video, usually RGBHV. This means each wire contains, respectively, Red, Green, Blue, Horizontal Sync, and Vertical Sync. It's generally less expensive to make go long distances than DVI, but DVI might result in slightly higher quality to a digital display (LCD, LCoS, DLP, Plasma) because you eliminate one digital-to-analog then analog-to-digital conversion in the process. Both can be used for incredibly high quality video, but as Mitchell mentions above, only DVI (and its sister, HDMI) supports the special HDCP handshake needed to get some sources with some media to enable full resolution analog HD output (Hollywood has apparently agreed not to set the flag on the discs that makes that happen until 2012).
Whew, that's a mouthful. ![[Smile]](smile.gif)
| IP: Logged
|
|
Joel N. Weber II
Expert Film Handler
Posts: 115
From: Somerville, MA, USA
Registered: Dec 2005
|
posted 05-31-2007 09:34 PM
I think it also depends what you are driving: if you're driving a CRT, 5 BNC is probably about as good as you can get; for an LCD, you're probably better off with a digital signal. I'm not sure about DLP, though I suspect it likes digital signals, too.
I have an old computer monitor at home that I haven't quite gotten rid of that uses 5 BNC input, and I have a cable that converts analog VGA to 5 BNC for that monitor. The cable is entirely passive, as far as I know. (VGA has some additional pins that aren't available with 5 BNC, which allow the computer to query the monitor's resolution.)
My experience with LCD computer monitors has been that DVI invariably results in sharp images; analog video sometimes has analog video artifacts, depending on how well the equipment is working. I would assume that LCD projectors are likely to work in the same way as LCD monitors in this regard.
| IP: Logged
|
|
Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
|
posted 06-01-2007 04:19 AM
quote: Joel N. Weber II
I think it also depends what you are driving: if you're driving a CRT, 5 BNC is probably about as good as you can get; for an LCD, you're probably better off with a digital signal. I'm not sure about DLP, though I suspect it likes digital signals, too.
Yes, CRT monitors are analogue; very few of them would take digital signals, I think I've only ever seen one, but they would be internally converted to analogue to drive the display. DLP is digital, and analogue inputs on projectors are internally converted to digital; in what form, I'm not sure.
quote: Joel N. Weber II
I have an old computer monitor at home that I haven't quite gotten rid of that uses 5 BNC input, and I have a cable that converts analog VGA to 5 BNC for that monitor. The cable is entirely passive, as far as I know. (VGA has some additional pins that aren't available with 5 BNC, which allow the computer to query the monitor's resolution.)
Yes, it's a passive cable, the RGBH and V signals are just the same as on the 5 BNC cables. This is also the case with the old Apple 15 pin monitor connection, though this provided more information about the capabilities of the monitor, hence the row of dip switches on manny of the Apple computer to VGA monitor adapters.
quote: Joel N. Weber II
My experience with LCD computer monitors has been that DVI invariably results in sharp images; analog video sometimes has analog video artifacts, depending on how well the equipment is working. I would assume that LCD projectors are likely to work in the same way as LCD monitors in this regard.
To be honest, I can't usually see any difference on typical small, low-cost monitors, but the difference does show up on some of the high-end ones which we have. I can also see the difference on a NEC cinema projector, connected via a Christie Cine IPM 2k.
A few other points:
There are several forms of DVI, if there are two pins missing in the centre of each row then it's single link, if all pins are there then it should be dual link, but sometimes isn't.
If there are four small pins grouped around the large flat pin at one end then it's DVI-I, if these are not there then it's DVI-D. DVI-D is purely digital, whereas DVI-I also carries VGA style analogue signals on the same connector. The four small pins carry RGB and one of the syncs, and the other signals are carried on some of the main pins. This enables an analogue monitor to be connected to a DVI-I port, or an analogue signal to be connected to a DVI-I input, via a simple passive adapter. Some of these adapers have only the pins required for the analogue signals at the DVI end, and this is sometimes referred to as DVI-A. There were a few CRT monitors which had a DVI connector, but accepted only analogue signals on it, just to confuse things.
Traditionally there have been major differences between normal video signals, and computer display ones, though this distinction is becomming blurred.
Since you are talking about RGBHV on 5 BNCs I suspect that you are dealing with computer signals, since the use of separare H and V syncs is unusual with 'conventional' video systems, at least as extrenal connections, obviously the signals exist within equipment. RGB on 'conventional' video systems (is there a correct term for non-computer type video?) tends to use a single composite sync sygnal, either carried on a fourth wire (RGBs), or on the green signal (RGsB). In Europe most domestic televisions can accept RGBS via a SCART connector. Many monitors with RGBHV inputs on 5 BNCs can also take RGsB or RGBs, using three or four of these connectors.
Traditionally 'conventional' video used negative sync, interlaced scans and fixed scan frequcncies, whereas computers used positive, separate syncs, non-interlaced scans and multiple scan frequencies. However, Video DVDs played on computers, progrossive scan video systems and HD television are changing that.
There is an alternative digital monitor connection, DFP, which is now obsolete, but still sometimes seen on older equipment. It looks a bit like a tiny Centronics parallel printer connection, and the signals are the same as single link DVI-D, so a passive adapter can be used.
Watch out for games consoles; some of them output RGBs, but the sync is a 5V TTL one, not the normal 0.3V of conventional video.
HDCP content protection is mandatory on HDMI and optional on DVI, (obviously only on the digital connections on DVI-I); it is not supported on other interfaces.
| IP: Logged
|
|
Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
|
posted 06-01-2007 06:54 AM
Some clarifications to Stephen's post
quote: Stephen Furley
Yes, it's a passive cable, the RGBH and V signals are just the same as on the 5 BNC cables.
This not necessarily true. The "VGA" connector (High Density 15-pin Dsub...aka HD15) has pins for separate H and V sync...the sync "return" is common and often all the returns end up going to the same electrical point at one end or the other or both (in the devices, but sometimes in the premade cables too). Since 4-wire system RGBS predate the 5-wire systems...most devices can deal with either though 5-wire is preferred.
The ability to tell the difference between analog video and digital video really depends on the source material and the display device. I've done "shootouts" with identical source material with one staying all digital and one using 5-wire analog and most of the people couldn't pick off the difference...with motion video you are unlikey to see the difference. For static images that have sharp black to white transistions...you can often see which one is analog, if you know what you are looking for.
One thing DVI should do is have the devices handshake with each other to come up with the highest resolution both can handle...I have found though that sometimes it is better to go the analog route if the display device does not have as high a resolution as the source (non-HD display but HD source)...high quality scaling beats least common denominator.
quote: Stephen Furley
Since you are talking about RGBHV on 5 BNCs I suspect that you are dealing with computer signals, since the use of separare H and V syncs is unusual with 'conventional' video systems, at least as extrenal connections, obviously the signals exist within equipment. RGB on 'conventional' video systems (is there a correct term for non-computer type video?) tends to use a single composite sync sygnal, either carried on a fourth wire (RGBs), or on the green signal (RGsB). In Europe most domestic televisions can accept RGBS via a SCART connector. Many monitors with RGBHV inputs on 5 BNCs can also take RGsB or RGBs, using three or four of these connectors.
This one is riddled with differences between how Europe and the USA has handled video signals. Europe uses a "composite sync" which in the USA is normally referred to "Cvs" to distinguish it from a combined horizontal and vertical sync "S". They are NOT the same. A composite sync signal will carry the full composite signal (plug just that wire into the "video" input on the monitor and you got yourself a full colo(u)r signal). Not so in other parts of the word...the "S" cable just has the sync pulses.
When European equipment is used in the US...stuff with SCART connectors, one needs a device that understands composite sync OR you can use a device that strips the sync information out of the composite sync.
Pre-digital players...professional video used RGBS and later RGBHV. Most non-digital A/V systems nowadays are wired fully 5-wire.
Sync on green (RGsB) also is supported by many devices.
Most professional (broadcast quality) VTRs now have SDI outputs which make wiring a whole bunch easier/cheaper and retain a very high-quality signal, even over long distances using coax.
As Stephen has noted...things changed for the HD world for both analog and digital. For analog, "Component" was given the nod with Y,Pb,Pr and the sync went from the traditional "bi-level" to a "tri-level" sync.
| IP: Logged
|
|
Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
|
posted 06-01-2007 08:20 AM
You have to be careful with terminolgy; words have come to have different meanings, either officially or unofficially, over the years, or in different places. 'Composite' for example; in black and white days composite video was combined video plus sync, as opposed to non-composite video with separate sync. However, the same word is used when referring to a composite sync signal, i.e. combined horizontal and vertical syncs on one cable, as opposed to separate horizontal and vertical syncs with computer monitors. Then of course when colour arrived composite video came to have the meaning which is most common today, i.e. a PAL, NTSC or SECAM signal.
'PAL' and 'NTSC' now tend to be used to refer to 625 and 525 line systems, rather than just to the strict meaning of the colour systems involved. Of course, that causes problems with Brazilian PAL M, plus various semi-converted formats like PAL 60 and NTSC 4.43.
'VGA' tends to be used for the 15 pin analogue computer monitor connection, even though we long ago moved on from the original VGA specifications for resolution, etc.
quote: Steve Guttag
This one is riddled with differences between how Europe and the USA has handled video signals. Europe uses a "composite sync" which in the USA is normally referred to "Cvs" to distinguish it from a combined horizontal and vertical sync "S". They are NOT the same. A composite sync signal will carry the full composite signal (plug just that wire into the "video" input on the monitor and you got yourself a full colo(u)r signal). Not so in other parts of the word...the "S" cable just has the sync pulses.
When European equipment is used in the US...stuff with SCART connectors, one needs a device that understands composite sync OR you can use a device that strips the sync information out of the composite sync.
I think what you are saying here, if I have understood you correctly, is that over there you use the phrase 'composite sync' to mean what we would call a composite video signal, i.e. video plus sync. 'Composite sync' to us is combined horizontal and vertical syncs, but no video. This is another area where SCART has added to the confusion; in composite mode video is out on pin 19, in on pin 20, with a common return for both on pin 17. In RGB mode, R,G and B signals are on pins 15,11 and 7, each with its own ground, on pins 13, 9 and 5. There are no 'in' and 'out' connections for RGB, because it was originally intended for use with computers; so the same pins were 'out' on computers, and 'in' on televisions. This was in the days when many home computers put out 625 line interlaced signals.
SCART originally had no provision for S-video; it was later added, using the composite pins for 'Y', and the 'R' pin for 'C'. This means that different pins are used for each direction for 'Y', but the same pin is used in both directions for 'C'
Because SCART uses the composite pins for sync when working in RGB mode, Different pins are used for 'in' and 'out' for sync, but the same ones for R,G and B. Also, because the composite pin is used for sync, just about all domestic televisions can accept a full composite video for use as a sync with RGB, as anything going into this input will find its way to the sync separator in the set, but a lot of professional equipment with BNC connectors cannot; it requires a composite sync signal, i'e' combined horizontal and vertical, but no video.
SCART was a good idea, but it was badly implemented, and it's a mess. That's quite apart from the horrible connector.
With domestic equipment, using SCART at both ends, you only need one type of cable, there are no 'crossed' or 'uncrossed' versions as there are with DIN audio cables, and generally if you use a SCART connection you will get the best quality picture that the equipment is capable of. With more recent equipment you even stand a good chance of getting the correct aspect ratio automatically.
quote: Steve Guttag
Pre-digital players...professional video used RGBS and later RGBHV. Most non-digital A/V systems nowadays are wired fully 5-wire.
Most that I've seen has been RGBS on 4 BNCs; maybe I'm seeing older equipment.
quote: Steve Guttag
Sync on green (RGsB) also is supported by many devices.
Sony seem to have been quite keen on it.
quote: Steve Guttag
Most professional (broadcast quality) VTRs now have SDI outputs which make wiring a whole bunch easier/cheaper and retain a very high-quality signal, even over long distances using coax.
It's a pity domestic and even semi-pro DV equipment don't have it. The only digital connection you tend to get there for video is IEEE 1394. I've not yet seen a converter to DVI, there are converters to SDI, but they're expensive, and the Cine IPM 2k doesn't have a SDI input without buying a (also expensive) input module for it.
quote: Steve Guttag
As Stephen has noted...things changed for the HD world for both analog and digital. For analog, "Component" was given the nod with Y,Pb,Pr and the sync went from the traditional "bi-level" to a "tri-level" sync.
Can you explain what you mean by a 'tri-level' sync? I've heard of it being used for HD, but I'm not clear how it works. The only HD that I've had any dealings with so far has been with a couple of clips played from my laptop, via DVI into either DVI or HDMI.
AT least with film if you hold it up to the light you can tell what you've got; ok, you can't tell a Dolby 'A' track from an SR one, and you may not be able to tell what aspect ratio it is, but you cn generally work those out if you run it. At least you don't have any difficulty getting picture on screen and sound coming out of speakers.
| IP: Logged
|
|
|
|
|
|
|
|
All times are Central (GMT -6:00)
|
|
Powered by Infopop Corporation
UBB.classicTM
6.3.1.2
The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion
and agrees to release the authors from any and all liability.
|
Home
Printer-friendly view of this topic