When it rains it pours. I’m sure many of you are tired of hearing me talk about cables but it’s a topic that just keeps on giving. The other day I clicked over to an article on Positive Feedback written by Dave Clark that tries to explain why USB digital cables can make a difference. Dave apparently asked a few of his cable designer friends to help clear up any confusion about a few misplaced ones and zeros. You can read the piece for yourself by clicking here.
I could go through every paragraph and comment on the points made by the writers but I think I can sum up their approach in a few paragraphs.
One common focus seems to be on “data errors that cause audible losses” because of the lack of error correction, noise in the cable, or a loss of waveform fidelity. It’s true that music data can suffer from transmission problems under unusual circumstances, but the reality is that a 1-meter length of good quality USB cable can successfully deliver the ones and zeros virtually 100% of the time. Contrary to the repeated claims made by the designers, there is only a problem if the data is severely corrupted. And it would have to be corrupted a whole lot to damage the fidelity of the digital signals traveling 1 meter. In the real world, all of the data bits are successfully delivered from the source to the destination…in spite of any background noise or compromised data waveforms. All we have to do is get the data in tact, and then we can rebuild the analog waveform.
The second aspect of USB infallibility are the timing errors that are the result of “reflections and clock inaccuracies” inside the cable. The reality is that jitter is not an issue in a well-designed DAC because the incoming (jitter damaged) clock is not used…AT ALL. The electrical engineers that design and build high end DAC know that jitter can be a problem and they go to great lengths to use their own clocks inside their devices…clocks that are highly accurate and virtually jitter free. So the cable designers could well ignore any potential clocking errors in their expensive cables.
The final point made by the cable designers is the power lead that is part of the USB connection. The claim is made that the “transmission of power from the host to unpowered USB devices. The 5V power legs within a USB cable can also cause problems with the integrity of the D+ and D- signals if not properly isolated”. But what if the power is properly isolated as is the case in high end systems? Why bother talking about the potential problems when in the real world of high end audio they rarely if ever exist?
The gist of the articles is that certain bad things CAN happen to a digital stream. And those bad things have the potential to modify the audio moving from a source to a destination. But in the real world folks, those potential problems don’t happen or they happen very, very rarely. So would you accept the cost and logistics of building a 20-foot high sand bag barrier around your house in the Mojave Desert to protect your property from the once in a 100-year flood?
Think about the title of the article…”Why USB Cables CAN Make a Difference”. Then consider these two things: who contributed to Dave’s article and what would motivate them to overstate the “problems” with USB digital cables.