Jul/090
Why are HDMI cables so expensive?
The rules of supply and demand don’t apply to cables. A Best Buy in downtown Boston charges $140 for name-brand HDMI cables, which connect high-definition video to big-screen TVs. The Radio Shack a few blocks away wants $50 for its generic version. Online, Amazon will sell you HDMI cables for $5.
Ostensibly, the products are identical. So why the huge disparity in price? Is there a difference between the three products?
Not really.
The prolific review crew at CNET put it more harshly. “Those cables are a rip-off,” says the website’s guide to HDMI. “You should never pay more than $10 for a standard six-foot HDMI cable.”
CNET’s editors regularly use inexpensive options for both professional tests and in their own home theaters. There’s no distinguishable drop in picture quality, they say. Any cable that caused unwanted dropouts or flashes was simply defective, something that can occur with all electronics – and no brand had consistent problems.
Consumer Reports, How Stuff Works, Popular Mechanics, and trials by the Monitor agree. “Our tests indicate, you can expect flawless performance from any 4-meter cable, regardless of price,” writes PC World.
So why do salespeople praise the expensive kind? The secret is that stores don’t make much profit off TVs and video-game consoles. So to balance out the big items, most retailers mark up the little things.
For example, the retail watchdog Consumerist.com published a 2008 wholesale list from Monster Cables, the high-end brand that hawks some of the most expensive cords. The suggested retail price for its four-foot HDMI cable is $79.99. But it wholesales for $38.23 – less than half the sticker price.
Monster responded by saying that final prices are up to individual stores and that its suggested markup is “much less” than the margins on clothing, jewelry, and furniture.
The company says it takes pride in the quality of its cables. They’re built to withstand wear and tear, both within the insulation and where the connector meets the TV.
And Monster insists that its HDMI products are somewhat futureproof. HDMI is an evolving standard. Current cables, especially Monster’s, can deliver more information per second than their original HDMI ancestors. According to Monster, this matters with 1080p video, which is the sharpest on the market, and will mean even more if TVs move toward higher-definition pictures.
But again, many eagle-eyed reviewers stress that with TVs under 1080p (such as 480p, 720p, or 1080i), you can’t tell the difference. And since image quality is only as good as the weakest link, that top-notch standard only applies if both the TV and the video run at 1080p. For example, high-def broadcast TV channels stick to 720p or 1080i – and they’ll most likely remain that way for some time.
Online stores offer the best deals on cables. www.ukhdmi.com
Jul/090
What’s the Matter with HDMI?
How the designers of the HDMI standard screwed up, and what’s to be done about it.
HDMI, as we’ve pointed out elsewhere, is a format which was designed primarily to serve the interests of the content-provider industries, not to serve the interests of the consumer. The result is a mess, and in particular, the signal is quite hard to route and switch, cable assemblies are unnecessarily complicated, and distance runs are chancy. Why is this, and what did the designers of the standard do wrong? And what can we do about it?
The story begins with another badly-developed standard, DVI. A few years ago, there was a movement within the computer industry to develop a new digital video display standard to replace the traditional analog VGA/RGBHV arrangement still found on most computer video cards and monitors. Interested parties grouped together to form the Digital Display Working Group (DDWG), which developed the DVI standard.
DVI had all the earmarks of a standard designed by committee, and it remains one of the most confusing video interfaces ever. DVI could run analog signals, digital signals, or both, and it could run digital signals either in a single-link configuration (in a cable using four twisted pairs for the signal), or in a dual-link configuration (using seven). Identifying which DVI standard or standards any particular device supported was not always easy, and the DVI connector came in various flavors and was never really manufactured in any form that wasn’t well-nigh impossible to terminate.
But the worst thing about DVI was something that the computer-display professionals involved in its development really didn’t give much thought to: distance runs. Most computer displays are mounted at most a few feet away from the CPU, so it didn’t seem imperative that DVI work well over distance. This lack of concern for function at a distance, coupled with common use of twisted-pair cable (e.g., CAT 5) in computer interconnection, led to a decision that DVI would be run in twisted-pair cable.
Had the DVI standard been designed by broadcast engineers rather than computer engineers, things probably would have turned out very differently. In the broadcast world, everything from lowly composite video to High-Definition Serial Digital Video is run in coaxial cables, and for good reasons, which we’ll get to in a bit. Long-distance runs of VGA, in fact, are always handled in coaxial cable (though there may be a number of miniature coaxes in a small bundle, rather than something which obviously appears to be coax).
DVI lacked a couple of things which the consumer audio/video industry wanted. It was implemented on a variety of HD displays and source devices, but it was confusing for the consumer because of the many variants on the standard and different connector configurations, and it didn’t carry audio signals. A consortium to develop and promote a new interface, HDMI, was formed; the idea was to come up with a standard which could be implemented more uniformly, was less confusing, and offered the option of routing audio signals along with video.
Here, again, was an opportunity to avoid problems. The difficulties of running DVI-D signals over long distances were well known, and the mistakes of the past could have been avoided by developing HDMI as a wholly new standard, independent of DVI. Instead, the HDMI group elected to modify the DVI standard, using the same encoding scheme and the same basic interface design, but adding embedded audio and designing a new plug. Instead of many DVI options, analog, digital, single and dual link, there was one “flavor” of HDMI (actually, there is also a dual-link version in the HDMI spec–but you won’t find it implemented on any currently available device). This provided the advantage of making HDMI backward-compatible with some existing DVI hardware, but it locked the interface into the electrical requirements of the DVI interface. Specifically, that means that the signals have to be run balanced, on 100 ohm impedance twisted pairs.
We’re often asked why that’s so bad. After all, CAT 5 cable can run high-speed data from point to point very reliably–why can’t one count on twisted-pair cable to do a good job with digital video signals as well? And what makes coax so great for that type of application?
First, it’s important to understand that a lot of other protocols which run over twisted-pair wire are two-way communications with error correction. A packet that doesn’t arrive on a computer network connection can be re-sent; an HDMI or DVI signal is a real-time, one-way stream of pixels that doesn’t stop, doesn’t error-check, and doesn’t repair its mistakes–it just runs and runs, regardless of what’s happening at the other end of the signal chain.
Second, HDMI runs fast–at 1080p, the rate is around 150 Megapixels/second. CAT5, by contrast, is rated at 100 megabits per second–and that’s bits, not pixels.
Third, HDMI runs parallel, not serially. There are three color signals riding on three pairs, with a clock circuit running on the fourth. These signals can’t fall out of time with one another, or with the clock, without trouble–and the faster the bitrate, the shorter the bits are, and consequently the tighter the time window becomes for each bit to be registered.
Consider, by contrast, what the broadcast world did when it needed to route digital video from
Jul/090
Sky “considering” adding Dolby Digital 5.1 via HDMI to Sky+ HD boxes
Sky has exclusively told whathifi.com that “it’s currently investigating the possibility” of introducing Sky+ HD set-top boxes that transmit Dolby Digital 5.1 surround sound via the HDMI connection.
At the moment, Sky+ HD owners have to use an HDMI cable to transmit the picture from the box to the TV or projector, and a separate optical digital connection to their home cinema amplifier to output 5.1 surround sound.
“When we launched Sky HD, lots of users weren’t using HDMI [for sound], but we’re aware this is becoming more of an issue for some of our customers,” says a Sky spokeswoman.
There’s no timescale for when the change may be introduced, but Sky’s technical team is looking into it.
It’s become more of an issue recently, with some new-model multichannel amps and receivers automatically defaulting to HDMI for surround sound and bypassing the optical connection.
This means that in certain configurations current Sky+ HD boxes will only output stereo sound (via HDMI) to the amp or receiver, not Dolby Digital 5.1.
Sky is not alone in this regard, with other set-top boxes from companies such as Tiscali and BT Vision also outputting Dolby Digital 5.1 via the optical, not HDMI connection.
Last year Sony had to fix its STR-DG820 and STR-DA2400ES receivers so you could use the HDMI and optical inputs simultaneously, and this year Yamaha has run into the same problem with four of its 2009 models.
Even if Sky does decide to add surround sound via HDMI to its future set-top boxes, there are still one million or more existing Sky+ HD boxes in UK homes that need the dual HDMI/optical connection.