DVI-D & HDMI
(very) Frequently Asked Questions
Aurora frequently get asked many questions about DVI and HDMI. The global home cinema community is still trying to come to terms with what DVI and HDMI are, how they compare, what they do, what they're compatible with etc. Here's some of the most popular questions, with simple answers which will hopefully solve your queries...
- What's the difference between DVI-I and DVI-D?
- How about DVI dual link vs single link?
- Can I connect DVI-I to DVI-D?
- I want to use component video or RGB output and convert to DVI-D. Can I do this?
- What is DVI-D "HDCP"?
- What is HDMI, and how does it compare to DVI?
- Can I connect a DVI device to a HDMI device?
- Can I connect my analogue video output to HDMI?
- Are there any length restrictions with DVI and HDMI cables?
What's the difference between DVI-I and DVI-D ?
It's important to first note that "DVI" (Digital Video Interface) refers to the connector, or interface, only. It's application can vary. There are three main types of DVI; DVI-I, DVI-D and a third one which is rarely mentioned, DVI-A. This latter one is DVI "Analogue", which is quite obviously analogue only. This is essentially VGA (RGB-HV) in a different plug. DVI-D is at the other end of the scale, being pure Digital video only. DVI-I combines the two, containing both analogue and digital cores.
DVI-I does NOT convert ananlogue to digital. Rather it just provides a convenient connection to offer analogue or digital in the one cable. DVI-I and DVI-D can be distinguished by the presence (DVI-I) or absence (DVI-D) of four extra pins - two above and two below the flat horizontal location pin, as follows;
How about DVI dual link vs single link ?
A "Single Link" DVI connection contains three data channels for digitized RGB information (called "Transition Minimized Differential Signaling"), offering a bandwidth which can support up to 1920x1080 HD progressive resolution. "Dual Link" has a secondary parallel connection of the same digital RGB "T.M.D.S." data channels, increasing bandwidth to a supported resolution of 2048x1536 progressive.
Most AV devices output only single link, but acquiring a dual link cable often costs about the same. Dual link is fully backwards compatible with single link, but the use of a single link cable cannot support the larger bandwidth if the need arises. In other words, it's recommended to buy a dual link cable to begin with.
Single link and dual link are both applicable to either DVI-D or DVI-I, but relates only to digital information being carried; ie:- it has no bearing on the analogue part of DVI-I. Single link can be easily identified by it's lack of the center two rows of pins in the connector, whereas dual link has all pins present. The diagrams following show this more clearly (the pins in question have been colored RED on the dual link diagram for clarification);
Can I connect DVI-I to DVI-D ?
Well... sometimes. Only the digital part of the signal will be relevant if they are connected, as the DVI-D connection cannot read the analogue signal which may be contained in the DVI-I. For example, if a DVI-I output of an AV device is outputting only an analogue signal, then you can't connect it to the digital-only DVI-D input of your display device, even though the plug may physically fit (although many DVI-D sockets don't have the provision for the extra pins of DVI-I, hence connection may not even be possible). You'll need to check that the DVI-I output is capable of passing DVI-D before attempting the connection. If your output device has only Analogue DVI-I, then try connecting it to the VGA input of your display device by using an appropriate adapter (Cinema Cables cannot provide such adapters).
I want to use component video or RGB output and convert to DVI-D. Can I do this ?
No - there's really no point. Component video and RGB are both analogue signals (as are Composite and S-Video). To input these signals into a DVI-D connector would require an analogue to digital (A/D) conversion. Any display device which contains a DVI-D input already uses a digital circuit which contains an A/D converter for all analogue inputs. Using an external A/D converter would be unlikely to acheive any better result than that which is already built in to the display device.
The benefit of DVI-D is the lack of A/D or D/A conversion required at any stage. The pure digital signal output from a DVD player, digital TV tuner and the like would be sent to the digital display device (eg plasma, LCD, projector etc) totally intact. This yields the best possible result.
What is DVI-D "HDCP" ?
"HDCP" was developed to protect the intellectual property of software/movie studios and distributors. It stands for "High Definition Content Protection", and is a digital code buried within the bitstream which is output from the digital source. This prevents unauthorised copying of protected materials, much like Macrovision did for analogue recordings. Only since the introduction of this standard have hardware manufacturers been allowed to offer DVI-D or HDMI outputs on their DVD players, High Definition TV tuners etc. Any device which bears the label "HDCP" simply means that it is complaint with the requirements. It does not change the output signal in terms of quality, it only refers to the additional code which it contains.
DVI-D was originally used exclusively in the IT realm, but the introduction of HDCP saw it evolve into the AV industry. HDMI was then introduced after the HDCP standard was released, hence all HDMI products are now HDCP compliant (and don't necessarily say so).
What is HDMI, and how does it compare to DVI ?
HDMI stands for "High Definition Multimedia Interface". It is the latest standard which integrates the same digital video bitstream as DVI-D (Single Link) with up to eight channels of high-res digital audio. What's more, it is a two-way communicating bus, allowing a source and display device to "talk" to each other. For example, a display device (eg Plasma screen) can tell your source devcie (eg DVD) what format it wants to run in, and the DVD can output the appropriate signal. This is of course reliant on the manufacturers making their firmware compatible with this capability. It's essentially the modern-day SCART cable, containing both picture and sound.
The picture quality of DVI-D and HDMI will be identical, assuming the same standard of cable is being compared, as the video signal/bitstream is the same. HDMI differs in that it also contains audio, has communications ability, and takes up less real estate on a device's connections panel.
Can I connect a DVI device to a HDMI device ?
You can connect DVI to HDMI, providing the DVI is the Digital variety - ie: DVI-D. The signal is 100% compatible with no loss of quality. You can use either DVI-HDMI adapters, or a cable which is terminated with DVI-D at one end and HDMI at the other. Of course the extra features of HDMI will be forfeited (digital audio and communications bus), but otherwise it's fine.
You cannot connect DVI-I to HDMI, as HDMI is digital only. You'll find that most HDMI-DVI adapters do not have the facility for the additional four pins of DVI-I, hence a physical fit is not possible. Use only DVI-D cables with a HDMI adapter, or vice versa.
Can I connect my analogue video output to HDMI ?
No. HDMI is digital only - no exceptions.
Are there any length restrictions with DVI and HDMI cables ?
No, not with good quality cables. Both formats can theoretically run in excess of 100m, but in reality there are some restrictions, being cable sizes and price. HDMI cables will in future be capable of greater bandwidth than is currently being claimed, so increasing wire gauge (thickness) is favourable. Lengths under 10m, can safely use 28AWG cores. Lengths over this should really be doubled in core thicknesses, but Cinema Cables chooses a little more again at 24AWG (approx 230% larger than 28AWG).
DVI cables do not require the same attention in core gauges, but we're comfortable at a 28AWG limit of 20m.