Refer to this thread:
Why you shouldn't buy cheap HDMI cable (
http://forum.lowyat.net/topic/738072)
(Source)
http://www.audioholics.com/education/cable...ble-bench-testsDigital Is Digital, Right?Unlike the mumbo-jumbo surrounding TOSlink and coax optical cables, HDMI is a little more complex. When the specification is a constantly-moving target, as HDMI has proven to be - and this has been fueled by a willing consumer electronics industry - things get a little hairy. It's important to understand just why, with HDMI, you can't just say "digital is digital, it either works or it doesn't." As we referenced in detail in our article 'HDMI - It's All in the Bitrate,' HDMI has progressed (evolved) from a simple 720p/1080i 8-bit per channel signal to the current 1080p 12-bit (or more) per channel signal it is today. Just what kind of bandwidth is being sent over the cable depends on the source electronics and the capability of the display, but the potential has vastly increased since the debut of HDMI in 2003. As these signals got higher in resolution and bit depth, the amount of bits per second traveling through the HDMI cable increased. When that happened (and most recently culminating in the release of HDMI 1.3) the tolerance requirements for HDMI cables changed as well.
By way of example, with a digital audio coax cable you are dealing with a required maximum bitrate of just over 3 Mbit/s. For a S/PDIF connection, be it TOSlink or digital coax, this is chump change. The specification for that digital connection hasn't changed since ~1997 and the demands made on the cable are far less than the cable's potential capabilities. Now let's look at HDMI. A massive bundle of 15 cables (not including drain wires) - some insulated, all fairly important. In order for HDMI to remain practical, and avoid unnecessary interference, the cable has to be made, at least partially, out of stranded wire, lest 15 solid cables render the cable more of an unbendable, unwieldy stick than a cable. Additionally, the amount of information necessary to transmit the incredibly high resolution video and 8-channels of uncompressed digital audio far exceeds that of the typical DTS or Dolby Digital compressed traffic which meanders through a S/PDIF audio-only connection.
So How Do Cables Differ?Aside from cost, HDMI cables differ in many ways. Some real obvious differences include the gauge of cable used in construction, stranded versus solid cable pairs (which greatly affects flexibility), and flat versus round. These physical differences are significant, but not nearly as important as whether or not the cables are rated to carry a particular signal a stated distance. Many cables are certified by one or more companies who provide specifications and/or speed ratings to cables. Simplay, for example is a wholly-owned division of HDMI Licensing, LLC that charges large sums of money to test cables and consumer electronics for compatibility and interoperability. Another company coming online is DPL Labs which rates cables on a 1-5 rating. It's a bit redundant since it should be pretty obvious that the Category 1 and 2 specs should be easy enough to certify and uphold. We're more concerned with manufacturer being honest than whether or not some third party certifies them or gives them a sticker. After all, nobody expects every AV receiver to be certified by a third party for exact power ratings (the FCC notwithstanding, but they hardly do more than ensure the product doesn't emit radiation).
Specific problems arise in a couple of areas. First, the equipment required to test HDMI cables is very expensive. We're talking over $200,000 for a basic setup including source generator, scope and calibrated HDMI "probes". This is obviously cost prohibitive for smaller companies to do much more than rebrand someone else's manufactured cables that have already been certified. If they choose the right manufacturer this isn't a problem, but some don't.
You can predict cable integrity and performance fairly accurately by doing the math on the cable geometry and modeling the results. This isn't easy, however (at least not for mere mortals) and we opted to use the measurement methodology instead. For a great (though very technical) article on HDMI cable modeling, please see Eugene Mayevskiy's writeup, which comes from an engineer who worked with Tektronix to deal with these very issues.
This post has been edited by DigitalTech: Apr 12 2010, 11:23 AM