So you’ve just spent a bundle on a new HDTV or a home theater system. You’re about to head for the register, and the salesperson suggests that since you’ve invested so much in your system, it needs expensive cables to give you optimal performance.
If visions of rust-proofing and high-end floor mats come to mind, you may be on the right track. Ever since Monster Cable started operations decades ago, the myth that “more expensive cables are better” has been heavily promoted to the A/V consumer. It’s true that we should all avoid poorly-made cables, but whether there’s anything out there that will give you better performance than, for example, Radio Shack’s “gold” cables, has yet to be proved. Years ago, Stereo Review magazine (now Sound and Vision) did a true double-blind study of premium cables. A few of their testers discerned a very slight difference between cables, but no improvement was detected.
But that’s all old history, we’re told, because those cables were “analog.” With new “digital” cables (e.g., HDMI), quality is more important than ever. Indeed, the term “digital” sounds more complicated and less familiar, so we’re inclined to accept what we’re told. Still, knowledge is power, so let’s examine the facts.
In actuality, all signals are analog in nature. So all signals need a reasonably good wire to travel un-degraded from point A to point B. True analog signals travel as a continuously changing voltage, which must be faithfully reproduced on the far end of the cable. Equipment can tolerate a small amount of degradation, but significant disruptions will be reproduced, uncorrected, in your speakers.
Digital signals also travel as a continuously changing voltage, but the signal alternates between two levels; one near the maximum voltage, and the other near zero. The receiver samples the signal only when it is known to be stable, and measures only whether the signal is above or below a middle threshold. A high voltage is considered a “1”, and a low voltage is considered a “0”. Below are two traces showing consecutive 0s and 1s. Both would produce equivalent data.
As long as the digital signal isn’t degraded so much that the 0/1 measurement is made in error, the receiver will receive the transmitted signal with no imperfections. Even better, most signals include extra data bits used to check and reconstruct the transmitted data, so that even if an occasional 0/1 is received incorrectly, it can usually be fixed, again resulting in a perfect signal.
A higher quality cable may increase the difference between the high and low voltages, but anything better than “good enough” does not provide an improvement. An acceptable 0 or 1 (upper trace) and an exemplary 0 or 1 (lower trace) convey the exact same information.
So how do you know if your cable is good enough? Analog signals degrade gracefully. A slightly-damaged analog signal can sound very similar to a good one, such that only trained ears might hear a difference. However, with a digital signal, the effect of even a few uncorrected 0s and 1s is likely to create obvious distortion of picture or sound. Thus, if your HDMI signal sounds and looks good, it is most likely just fine.
Still, some cable manufacturers promote features that can be of little benefit. It’s not that these features don’t improve the wire, but once the wire is “good enough,” making it even better really doesn’t provide any benefit. A car that can travel 140mph may not benefit someone who never drives over 60.
Two features, lower-gauge (e.g., thicker wire) and twisted-pair, have some benefit in certain situations. For speaker wire, many authoritative sources provide tables for distance vs. gauge. However, exceeding the recommended gauge provides no further advantage. Twisted pair is already common in digital cables (e.g. HDMI). It’s appropriate for long multi-room runs, and can help reduce interference for line-level analog signals (like the connections between your audio components and receiver). But don’t bother upgrading unless you’re actually overhearing someone’s CB radio.
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Jeff Winston has been writing about home electronics since 1998. An electrical engineer, Jeff has contributed to the development of products in the computer, consumer electronics, and wireless industries. He spends his spare time with his wife, kids, and many PCs, sometimes in that order.