A critical look at HDMI

So what are these secretive aspects? Have you come across DVD players at $29, or even as low as $19? And shopped around for cables to connect these handy, high-performance devices to your television sets? And wondered why the cables are 10 times as expensive, or at their cheapest, just as expensive as the compact DVD players? As an engineer, I'll admit to being shocked when I first came across a DVD player at $19. This is a Digital Versatile Disc player that provides high-definition images in real-time video, including sophisticated mechatronics, optoelectronics, motors, sensors, lasers, remote control, and sophisticated high-performance integrated and discrete electronics as well as power conversion and delivery that enables its operation. All this for $19, to me as an engineer, is magic. But this makes sense; it is the magic of integration and volume production that is the beauty of commerce, benefiting the simple consumer. What doesn't make sense to me is the cost of the cable to connect such a wondrous device to a television. It is akin to having to pay 10 times what you pay for a soft drink for the straw you use to sip your drink. Would you, kind reader, pay $10 for a plastic straw?

Blogs and online articles [see 2] make admirable attempts to educate the consumer. Following that example, I'll share and entertain with this engineer's insights into HDMI, and electronic communications cables in general.

It all began with USB
Or perhaps, with Firewire, the IEEE 1394 standard (an industry-wide standard) that has also been adopted as the High definition Audio-Video Network Alliance (HANA) standard connection interface for A/V component communications and control.

USB came right along about a year or so later in 1996, with similar user-friendly features, but lower speed. But what I am talking about is the marketing of such cables. Recall seeing advertisements that indicated that if you buy the 'better' USB cable, the print quality out of your printer will be better?

Let's dissect that argument and understand it a bit. These communications standards deal with digital data transmission over serial links. Put simply, information is transmitted bit by bit in sequence, at relatively high speeds, and USB started out with 12 million bits per second. Some of these bits transmitted could be recognized incorrectly at the far end, even though these are black-and-white symbols (digital, binary, true-or-false symbols) transmitted. These errors (corresponding to a Bit Error Rate, BER, of the cable) relate to picture quality, and presumably, the 'better' cables offered lower BER.

When the next version rolled along as USB 2.0, the standards group settled on 480 million bits of information per second, a 40 times increase in the bit-rate. More interesting than the puzzling 40X increase was the fact that the very same cables that were meant to transmit 12M bits per second could be employed to transmit the 480M bits per second without failing the standard!

One would rightly think that increasing the data throughput by 40X should amplify BER in the so-called 'worse' cable. BER is related to signal loss, and signal loss is strongly correlated with data throughput and corresponding frequency. Figure 1 shows signal losses vs. frequency on a 2-meter long, 50-ohm signal interconnect.