What is SDI?
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It stands for "Serial Digital Interface". Its just a serial digital connection scheme, which can be used to connect video components together if they are so equipped. For our purposes, the important thing is that its a way to connect a standalone DVD player's digital video output to a scaler.
Currently you either use something like an HTPC, where the scaler is software based and has direct access to the digital data, or you have to send analog out from the DVD, to a scaler that resamples it, scales it, then sends it back out as analog again.
That round trip from digital to analog to digital to analog, costs you in terms of quality. A digital video connection from the DVD player to the scaler solves that problem for standalone components, and you don't lose anything relative to something like an HTPC (or Faroudja's all in one DVD/Scaler box.)
Currently you either use something like an HTPC, where the scaler is software based and has direct access to the digital data, or you have to send analog out from the DVD, to a scaler that resamples it, scales it, then sends it back out as analog again.
That round trip from digital to analog to digital to analog, costs you in terms of quality. A digital video connection from the DVD player to the scaler solves that problem for standalone components, and you don't lose anything relative to something like an HTPC (or Faroudja's all in one DVD/Scaler box.)
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It is highly standardized both SMPTE and CCIR. It is a broadcast grade interface that has been around since the late 1980s. There are several versions for composite digital, component digital, and HDTV.
143mbs for composite NTSC,
177mbs for composite PAL,
270mbs for component digital 525 or 625,
360mbs for 16x9 component digital 525 or 625
1.5gbs for HDTV 1080i/30, 1080p/24, and 720p/60
Electrical properties are 75ohm impedance at 800mv level.
It is a one way connection meaning and input and output cable is needed, it can't carry bi-directional communications on one cable. It carries some limited control information that would not be of much consumer use.
Because it is so widely used in today's broadcast systems, there are low cost chip sets from several manufactures. This enables some niche high end consumer companies to utliize this technology. The SDI referred to in this forum is the 270mbs variety.
| Originally posted by Swampfox Is this standardized? Is it firewire? SM |
143mbs for composite NTSC,
177mbs for composite PAL,
270mbs for component digital 525 or 625,
360mbs for 16x9 component digital 525 or 625
1.5gbs for HDTV 1080i/30, 1080p/24, and 720p/60
Electrical properties are 75ohm impedance at 800mv level.
It is a one way connection meaning and input and output cable is needed, it can't carry bi-directional communications on one cable. It carries some limited control information that would not be of much consumer use.
Because it is so widely used in today's broadcast systems, there are low cost chip sets from several manufactures. This enables some niche high end consumer companies to utliize this technology. The SDI referred to in this forum is the 270mbs variety.
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Firewire wishes it was as standardized as SDI (AKA D1)...
Firewire also carries audio & comes in a few flavors (MPEG, DV) which do not talk well with eachother. It's also multidirectional (i.e., more than one device can talk).
SDI components are unidirectional (you have one side sending and one side receiving), no audio support. All SDI components talk the same language & can understand the others.
Both SDI & Firewire have pretty much the same video capabilities (in terms of enough bandwidth for SD, but not beyond)
HD-SDI is on the horizon too (not for us consumers, though).
Firewire also carries audio & comes in a few flavors (MPEG, DV) which do not talk well with eachother. It's also multidirectional (i.e., more than one device can talk).
SDI components are unidirectional (you have one side sending and one side receiving), no audio support. All SDI components talk the same language & can understand the others.
Both SDI & Firewire have pretty much the same video capabilities (in terms of enough bandwidth for SD, but not beyond)
HD-SDI is on the horizon too (not for us consumers, though).
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"HD-SDI is on the horizon too (not for us consumers, though)."
Why not for consumers? It should be here within a year or so.
Why not for consumers? It should be here within a year or so.
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Guys - help me out here.
The reason SDI is used in broadcast is not because of quality - it is because of quality over *distance*.
I have spoken with broadcast technicians on this SDI issue on DVD and they keep bringing it back to: "Who cares if it's SDI - you are still using the compressed video version of the data. SDI is only ever needed to maintain signal quality over distance - it won't make any difference because you are
accessing the digital data only after compression."
So, is this view correct? And has anyone ever done an A/B comparison between SDI and the 'traditional' video feeds.
Max Christoffersen
The reason SDI is used in broadcast is not because of quality - it is because of quality over *distance*.
I have spoken with broadcast technicians on this SDI issue on DVD and they keep bringing it back to: "Who cares if it's SDI - you are still using the compressed video version of the data. SDI is only ever needed to maintain signal quality over distance - it won't make any difference because you are
accessing the digital data only after compression."
So, is this view correct? And has anyone ever done an A/B comparison between SDI and the 'traditional' video feeds.
Max Christoffersen
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Your friends are correct on the first point. It can go long distances - up to 1500 feet with the right cable. On the second point I don't think they are seeing the whole picture (no pun intended) of SDI with DVD or DBS.
If you are just feeding your DVD into your TV, yes SDI would not make much sense as three analog component cables would yeild the same quality. The TV is analog anyway. Now some purists will rightly claim if your external SDI to analog convertor is superior to that in the DVD player, there would be some quality improvement. If your TV was 100 feet from your DVD player, again SDI feeding a DtoA at the TV would means no loss or noise pickup over that long cable run. But both these improvements are very subtle.
The big advantage of SDI is feeding external scalers and processors. As these devices work in the digital domain, it makes the most sense to feed them a digital signal. Otherwise they need to re-digitize the incomming YpBpR or worse yet, Svideo, composite video. SDI makes a significant improvement here.
Put it to your broadcast friends this way, if they need to make a dub between two digital VTR's such as Digital Betacam, how do they do it? A digital link or an analog link. An analog link means encoding the component digital to NTSC or PAL and back to component digital again on the record deck. We SDI fans here feel the same way, we want the best possible signal transfer into our scalers / upconvertors.
| Originally posted by [email protected] Guys - help me out here. The reason SDI is used in broadcast is not because of quality - it is because of quality over *distance*. I have spoken with broadcast technicians on this SDI issue on DVD and they keep bringing it back to: "Who cares if it's SDI - you are still using the compressed video version of the data. SDI is only ever needed to maintain signal quality over distance - it won't make any difference because you are accessing the digital data only after compression." So, is this view correct? And has anyone ever done an A/B comparison between SDI and the 'traditional' video feeds. Max Christoffersen |
If you are just feeding your DVD into your TV, yes SDI would not make much sense as three analog component cables would yeild the same quality. The TV is analog anyway. Now some purists will rightly claim if your external SDI to analog convertor is superior to that in the DVD player, there would be some quality improvement. If your TV was 100 feet from your DVD player, again SDI feeding a DtoA at the TV would means no loss or noise pickup over that long cable run. But both these improvements are very subtle.
The big advantage of SDI is feeding external scalers and processors. As these devices work in the digital domain, it makes the most sense to feed them a digital signal. Otherwise they need to re-digitize the incomming YpBpR or worse yet, Svideo, composite video. SDI makes a significant improvement here.
Put it to your broadcast friends this way, if they need to make a dub between two digital VTR's such as Digital Betacam, how do they do it? A digital link or an analog link. An analog link means encoding the component digital to NTSC or PAL and back to component digital again on the record deck. We SDI fans here feel the same way, we want the best possible signal transfer into our scalers / upconvertors.
SDI (as far as the broadcast interpretation of it goes) is not compressed.
The big advantage has already been stated.
The disc is digital with an Analog output.
The Scaler is going to take in analog, convert it to digital and then back to analog.
If we feed it digital, then the decoder and the a/d conversion does not have to happen. More importantly, the device does not need to "guess" what the signal is.
THe source is still whats important... crappy digital or crappy analog is still crappy.
The big advantage has already been stated.
The disc is digital with an Analog output.
The Scaler is going to take in analog, convert it to digital and then back to analog.
If we feed it digital, then the decoder and the a/d conversion does not have to happen. More importantly, the device does not need to "guess" what the signal is.
THe source is still whats important... crappy digital or crappy analog is still crappy.
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No-one would disagree with the garbage in equals garbage out equation; ie The 'crappy source'. This is equally true for digital audio transfer, with which I am way more familiar.
I think the pro guys are saying; "Compressed DVD is a crappy source anyway..you're rearranging the deck-chairs on the Titanic..what you really want is access to the bit-stream before it is compressed."
And if the analogue cable links are short between the player and the processor, (we have to assume the 'compression issues' are managed well inside the player), what *viewable* benefit is there to SDI?
On paper it looks to eliminate a step. But this is also true of progressive done inside the player vs outside the player. For me I can see no immediately discernable difference when comparing a progressive player vs an external doubler.
That's why I am asking for screen shots SDI vs 'Normal'.
The theory sounds right on the money - one less conversion step *should* make a difference; but *really* - do we have any shots in the forum of side-by-side SDI vs analogue?
Max Christoffersen
www.audioenz.co.nz
I think the pro guys are saying; "Compressed DVD is a crappy source anyway..you're rearranging the deck-chairs on the Titanic..what you really want is access to the bit-stream before it is compressed."
And if the analogue cable links are short between the player and the processor, (we have to assume the 'compression issues' are managed well inside the player), what *viewable* benefit is there to SDI?
On paper it looks to eliminate a step. But this is also true of progressive done inside the player vs outside the player. For me I can see no immediately discernable difference when comparing a progressive player vs an external doubler.
That's why I am asking for screen shots SDI vs 'Normal'.
The theory sounds right on the money - one less conversion step *should* make a difference; but *really* - do we have any shots in the forum of side-by-side SDI vs analogue?
Max Christoffersen
www.audioenz.co.nz
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I must disagree with that. And I am a "pro guy" and work in one of the largerst DVD mastering facilities in the USA. A properly mastered DVD rivals the source. Remember the compression is TEMPORAL, not SPATIAL. And most DVD's run an average of 10mbs. That's plenty for a typical movie with average action sequencies.
Now DBS is a crappy signal. It didn't used to be but the addition of too many channels has severely degraded the picture quality.
While it would be ideal to access the virgin uncompressed recording, that is not possible. So we are making the best with what's available to us.
| Originally posted by [email protected] I think the pro guys are saying; "Compressed DVD is a crappy source anyway..you're rearranging the deck-chairs on the Titanic..what you really want is access to the bit-stream before it is compressed." Max Christoffersen www.audioenz.co.nz |
Now DBS is a crappy signal. It didn't used to be but the addition of too many channels has severely degraded the picture quality.
While it would be ideal to access the virgin uncompressed recording, that is not possible. So we are making the best with what's available to us.
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Even if you doubt that its better, one way to look at is is that if you don't have to have lots of expensive circuitry to insure that you get a super high quality sample of the incoming analog signal, then you can do as good a job for a fraction of the price. An $800 HTPC can absolutely compete with a $10000 external (analog fed) scaler, because it gets the digital data straight off the disc and scales it. The expensive scaler has to have lots of expensive bits to sample that analog signal at very high quality, watch for 3/2 pulldown sequences, etc..., that a digital system doesn't require.
But, over and above that obvious advantage, it does make a difference. Plenty of people have moved to HTPCs from $1000 to $7000 and more external scalers. I moved from a $7000 Faroudja DVP-2200 to an HTPC, and the HTPC blows it away in terms of raw scaling quality, and because it can scale immaculately to almost any arbitrary resolution, and the results are super-crisp, and because it costs a fraction as much.
I'm going to move to a Leeza with an SDI input now. Its mainly a convenience thing. The reason we moved to the HTPCs was because of the high quality allowed by a direct digital connection to the scaler. But it has its rough edges that make it a PITA sometimes (particularly for me since my CQC work requires me to use it as a guinea pig a lot, so keeping it stable is hard.) But having an SDI connected scaler means we can get back to the convenience of CE devices, with all of the quality of an HTPC's direct digitial scaling.
But I compared the HTPC to my Faroudja while I had them both in the house (before the Faroudja was sold.) The HTPC was significantly crisper at the same resolution. And the fact that the HTPC can scale to exactly the resolution you need for your projector is just icing on the cake.
| The theory sounds right on the money - one less conversion step *should* make a difference; but *really* - do we have any shots in the forum of side-by-side SDI vs analogue? |
But, over and above that obvious advantage, it does make a difference. Plenty of people have moved to HTPCs from $1000 to $7000 and more external scalers. I moved from a $7000 Faroudja DVP-2200 to an HTPC, and the HTPC blows it away in terms of raw scaling quality, and because it can scale immaculately to almost any arbitrary resolution, and the results are super-crisp, and because it costs a fraction as much.
I'm going to move to a Leeza with an SDI input now. Its mainly a convenience thing. The reason we moved to the HTPCs was because of the high quality allowed by a direct digital connection to the scaler. But it has its rough edges that make it a PITA sometimes (particularly for me since my CQC work requires me to use it as a guinea pig a lot, so keeping it stable is hard.) But having an SDI connected scaler means we can get back to the convenience of CE devices, with all of the quality of an HTPC's direct digitial scaling.
But I compared the HTPC to my Faroudja while I had them both in the house (before the Faroudja was sold.) The HTPC was significantly crisper at the same resolution. And the fact that the HTPC can scale to exactly the resolution you need for your projector is just icing on the cake.
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Glimmie,
Do you mean 10 mbs with the SDI overhead? Otherwise 10mbs is a little on the high side for an "average" figure.
-Mr. Wigggles
Do you mean 10 mbs with the SDI overhead? Otherwise 10mbs is a little on the high side for an "average" figure.
-Mr. Wigggles
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10mbs is the high peak, average is about 4-5mbs. I didn't put that very well.
Once it's decoded, it's back to 1MBper frame, or 270mbs if serialized. The video will only have 10mbs or less of data. Being that it is temporally compressed, a still image can go out to 6.75mhz on luminance. It just can't do that 60 times a second in different places in the moving image. This is the difference between VHS and DVD. A VHS is spatial compression (in analog form) and it is not variable.
| Originally posted by MrWigggles Glimmie, Do you mean 10 mbs with the SDI overhead? Otherwise 10mbs is a little on the high side for an "average" figure. -Mr. Wigggles |
Once it's decoded, it's back to 1MBper frame, or 270mbs if serialized. The video will only have 10mbs or less of data. Being that it is temporally compressed, a still image can go out to 6.75mhz on luminance. It just can't do that 60 times a second in different places in the moving image. This is the difference between VHS and DVD. A VHS is spatial compression (in analog form) and it is not variable.
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