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In Reply to: RE: You know squat posted by audioengr on April 12, 2012 at 09:49:50
I'm sure that Belden has plenty of inexpensive cable that has a very nice eye pattern in lengths that fit within the USB protocol's timing budget. There is no science behind the mega-priced cables USB, it's marketing BS. The people marketing these cables undoubtedly lack sufficient knowledge of cable design, transmission line theory, driver and receiver circuitry, logic design, etc. There is real expertise in digital cables, but it resides in IC chip manufacturers such as Intel and cable manufacturers such as Belden.
Real engineers do not associate themselves with snake oil marketing.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Follow Ups:
Tony - you need to compare a $20 Belkin Gold (Which I incidently include with my USB converter) to the same length of Locus-Design Polestar playing music. The Polestar is not an expensive cable and not even the best out there, but absolutely kills the Belkin, and its more flexible. It's not marketing BS. I dont know that they even advertise this.
Belkin cable is a lot like all of the other "by-the-foot" cables on big spools made in China. Belden 1694A 75 ohm coax is the same. I have this too. They meet the specs for these types of cables, but it does not take much design skill to make something that sounds a lot better. Metals, dielectrics, shielding and geometries can all be improved.
Steve N.
There should be no audio signal going over a USB cable, only data. If there is an audio signal (i.e. a timed waveform that is correlated with the music) the design is broken, e.g. running in adaptive mode. If a USB cable effects the sound quality of a USB DAC then the USB DAC is not well designed. It may be that the best available USB DACs are not up to snuff, but if so the way to fix this is not a bunch of add-on band-aids. It is to do a better job of basic engineering. (But this is unlikely to happen because of the hockus-pokus snakoil nature of the high end audio mariet. I would look more to the pro-audio market, where the end users are technically knowledgeable so there is less room for nonsense.)
It's the same situation as with power cables. If a power cable affects the sound of the component attached it's because of poor design on the part of that component. A power cable is not supposed to be in the signal path. The situation is completely different with interconnects or speaker cables, where these wires are definitely in the signal path and have direct effect on the audio signal as well as directly interacting with the components on either end of the cable that are processing the signal.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
"If a USB cable effects the sound quality of a USB DAC then the USB DAC is not well designed."
This is what I though as well when I designed-in a multiple reclocked ASync USB interface. I had really hoped that this would be the case, but I learned different.
The reality is that these cables still matter, maybe not as much as when the interface was Adaptive, but they still matter. I dont know if its just impedance, shielding or common-mode rejection, but they still matter. Every single USB converter and DAC using async or block mode still improves by using a good USB cable.
I challenge you to design an async or adaptive interface that is completely immune to cable effects. Good luck.
All you have done is to indicate that you haven't been able to figure out what is going on. If changing the cable makes a real difference in the sound, why can't you track down what is going on?
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Why doesn't somebody just fix it? Because nobody knows what the problem is. All the obvious primary effects have long been taken care of. Secondary effects have been hypothesized, tested, determined which are causing problems and those dealt with, and still its not perfect. We are now in a situation where whatever is causing the issue is not obvious, and is almost certainly something difficult to measure.So someone comes up with a wild idea as to what it might be and tries to see if its possible to measure with existing test equipment. They come to the conclusion that it can't be measured by what's currently out there. So you go to a test equipment manufacturer and they say it will cost 20 million dollars to build such a piece of test equipment. The problem is we don't even know if the hypothesized effect is what is causing the issue. That's a lot of money just to find out if it is or is not the problem.
So what happens is people try and use existing test equipment that was designed to measure something else and see if its possible to coerce it into measuring what YOU want to measure, sometimes this works and sometimes it doesn't.
What frequently winds up happening is that you give up on trying to measure whatever it is and try and figure out a way to mitigate whatever it is (assuming that it exists), then build, that and listen, did something change? This process can take a long time and a lot of money, so you don't get to try out too many hypothesis per year. This process can take a long time to find the issue.
As an aside on this, my day job is designing chips that handle HUGE data rates. I can't tell you how many tera bits per second we are talking about, but it's a LOT of data. The cable that goes between boards that these chips are on costs $150,000, I kid you not. When you are working on the edge cables just plain cost a lot.
But I know you are going to say, but audio isn't going anywhere near as fast, so expensive cables are not necessary, BUT as Steve mentioned the level of the cable effects which are AUDIBLE are MUCH lower than the level which renders the link inoperable. These levels are in the same ballpark as what renders a link inoperable in the chips I work with. Why are such small levels audible? That's what we don't know yet. We do know that test equipment to work at these levels is extremely expensive, way out of reach of most audiophile companies. This makes going to the next level very slow.
It will happen, but it's going to take a lot of effort and wild goose chases to figure out.
John S.
Edits: 04/12/12
Thanks, John. I could not have said it better. At least I'm trying to resolve this. How many other manufacturers have a USB common-mode noise filter? Try zero. I'm the only one.
Steve N.
Right. The problems are elusive. And there's no real money in audio. And there are lots of scam artists, so that even if someone did happen to solve the problem there would be people out there "demonstrating" that the problem was still present, and this would diminish the already limited audiophile market. Another way of saying this is that the emperor has no clothes. Where is the little child?
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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