We look at the different types of HDMI cable and compare them to the different types of DVI cable, paying particular attention to video bandwidth. When it comes to PC video, they are neck and neck.
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Not Gone, But Lets Forget Them
Many connectors that are still very common with home theater equipment are analog. Our first article was devoted to pointing out the superiority of a digital signal, at least where computer video is involved. Our third told you how and when to upgrade to Digital Video Interface (DVI), and get High-bandwidth Digital Content Protection (HDCP) while you are at it. Therefore, anything we say about analog connectors in terms of computer video would be something of a history lesson.
We’ll keep it brief. In computer video signal terms: RGB is better than component, is better than S-Video, is better than composite, is better than co-ax, which, for runs over 10’-15’, is better than VGA. DVI is better than all of them. But how does DVI fare compared to other digital connectors?
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HDMI as Fast or Faster than DVI
There are several types of HDMI connection, defined by connector type, version, and cable category. Type C, also called HDMI Mini, connectors are used for small or portable devices. Type B is not currently available, so we will talk about it with other next generation options in a coming article. For now we focus on the more common Type A. The different connector types are physically different and not compatible. Cables of different versions or categories are physically identical and compatible, but offer different speeds and features.
The versions, from 1.0 to 1.3x, include numerous changes and additions. Focusing on video bandwidth in comparison with DVI, the significant difference is that versions 1.2x and earlier have maximum video bandwidth of 3.96 Gbits/s. That’s the same as Single Link DVI (we explained Single and Dual Link DVI in the second article in the series); enough for 1900x1200 resolution screens, with a 60Hz refresh rate and 24-bit color depth. Version 1.3x includes specifications for 2 categories of cable.
Category 2, or High-Speed, cable is able to support a faster connection than Category 1, or Standard cable (340 to 74.25MHz). A 1.3x, category 2 cable, offers video bandwidth slightly higher than DVI Dual Link; enough for a 2560x1600 screen @ 60Hz and 24 bit/px. A Category 1 cable limits bandwidth, from any version, to 2.23 Gbits/s total, meaning for audio and video combined (more on HDMI simultaneously carrying audio and video in a moment), they are suitable for 1080i or 720p and below. Thus, they are not a good idea for computer monitors. Even a monitor with an appropriately low resolution will have its bit/px, or colour depth, compromised.
Manufacturers don’t always include this information about their cables. Some will just specify a supported bandwidth. This is the total bandwidth for audio and video. Therefore, it is obviously higher than the bandwidths listed above for video only.
Category 1 cables of any version will claim 2.2, 2.23, or “over 2" or “over 2.2" Gbits/s.
4.8 or 5 Gbit/s indicates 1.2 or earlier with cat 2 cable, or the same video bandwidth as Single Link DVI.
Speeds “up to 10.2" or “over 10" Gbits/s indicate a 1.3 or later, with cat 2 cable, or slightly more video bandwidth than Dual Link DVI.
Provided you avoid Category 1 cables, HDMI is an able competitor against DVI in terms of computer video signal quality, delivering the same or slightly more bandwidth. But that is just the video bandwidth side. We’ll explain all of HDMI’s extra features, which is where it really shines against DVI, in the next article.