You are here

Log in or register to post comments
jorsan
jorsan's picture
Offline
Last seen: Never ago
Joined: Aug 2 2006 - 5:39am
USB cable: how long is too long

Hi, I need to run a 30ft USB cable from my computer to my audio system to play my Flac files thru my DAC there. I need to know if I could have some loss in the digital signal using a cable of this long or because is digital, the signal remains 100% perfect?. Just found this amplified cable:
http://www.usbmax.com/view_product_info....ategoryidds=102

Looks like this cable could do the job (as per the add), but need some profesional and honest comments from you to decide what is the best.

One more, how can I verify if Im loosing quality? will be interruptions in the sound or just degradation of quality? maybe a basic question but honestly dont have a clue about it.
Thanks in advance.

struts
struts's picture
Offline
Last seen: 2 months 2 weeks ago
Joined: Feb 1 2007 - 12:02pm
Re: USB cable: how long is too long

Although it is carrying digital signals, USB is fundamentally an electrical system that relies on voltage changes as its underlying mechansim. Since all wires have electrical properties such as resistance that are proportional to their length, the answer is yes, you do risk signal degradation if you exceed the specified performance envelope.

The USB 2.0 standard specifies a maximum cable length of 5m/16ft (so the simple answer to your question "how long is too long" is "longer than that") however the standard allows for this to be extended (up to 5 times) by inserting a USB hub. As it says in the description, this cable just has a bus-powered hub built in, so it looks like a perfectly valid solution. No snake oil there.

As with most communications protocols, USB includes a CRC check to ensure data integrity, however while CRC is very good at catching the sort of random errors common in data transmission it is effectively a statistical mechanism and doesn't guarantee data integrity. It is most likely that any data errors that do sneak through will manifest themselves as a noticable click or pop.

Timing errors are a far more complicated subject. USB connections can suffer from quite high levels of jitter or very low levels depending on the way the manufacturer has implemented the product (if you don't already know more than you ever wanted to about this subject my advice would be to ignore it - ignorance is bliss!) I think the simple answer is that either way this cable is unlikely to make a significant difference and for $22 I don't think you have much to lose.

I can't see any reason to recommend against trying this cable. Good luck!

jorsan
jorsan's picture
Offline
Last seen: Never ago
Joined: Aug 2 2006 - 5:39am
Re: USB cable: how long is too long

Thanks a lot Struts for your interesting lesson on USB cables and ..... you are right, sometimes ignorance is a "bliss".

RGibran
RGibran's picture
Offline
Last seen: 2 years 2 months ago
Joined: Oct 11 2005 - 5:50pm
Re: USB cable: how long is too long

IIRC, the Transparent (?) USB cable AD recently reviewed claimed lengths up to 50' with no loss!

  • X
    Enter your Stereophile.com username.
    Enter the password that accompanies your username.
    Loading