By USB spec I don't think a USB cable can be more then several feet....
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Yes, USB 2.0 spec is 15 feet. You may get away with longer with slower devices. Also, you just need a cable that meets spec - $20 or so. The only way a USB can "change the sound" is if somehow bits are uniformly changed to alter the sound in a uniform way. Or some bits get flipped and some samples are corrupt and substituted in the player with previous good samples. It's quite easy to determine if your cable is corrupting data. Just connect an external USB drive to your computer and cable and copy files with some sort of data verification (checksums, zip file intergrity test etc) and see if any files get corrupted compared to the source when reading it back. It's very unlikely you'll see and difference between a $20 cable and a $200 "audiophile" USB cable.
Thanks, Steve, for the reply. For $15 I decided to try the cable referenced above to satisfy my own curiosity. I connected it between my "front end" netbook and Ayre QB-9. I used my 5M USB 2.0 cable for a total of 15M of USB cable. I couldn't hear any differences. Sounded fine to me. Of course I don't have any equipment to take any type of measurements at the DAC input. And, I was only sending CD data, I don't have any higher rez PCM to try.
Let's not forget that Larry_s has an async USB DAC, where the clock is not recovered from the input stream and transport and interface jitter don't exist.
Kijanki, your friend might still be OK, though, and the low price of the USB cable justifies at least a try. What other decent interconnects could one use for the same price?
That's what I have (Benchmark DAC1) but I use Airport Express across the room instead of long cable, with 3' glass Toslink to DAC. AE has low (250ps) jitter, according to Stereophile measurements, that is further suppressed by Benchmark. My friend tried it a while ago but couldn't make it work. He returned it to Apple store and doesn't want to try again. It was most likely software setup issue.
Kijanki, I had the Benchmark and liked it, in general, but I found it to be far from jitter-immune. It responded to different transports and digital interconnects, which tells me that it didn't really knock out jitter.
It lowered it though, let's give credit where credit is due.
I bet that if you had a chance to listen to any asynchronous USB DAC you'll see what jitter-free really means and how wonderful computer audio can truly be. Throw in hi-res on top of that and you'll be thanking God for your ears, for without them your smile will go all-around your head ;-)