Length of USB Cable

Hi,

Anyone out knows the maximum length of a usb cable from notebook to DAC can be before any reduction of signal sets in? I intend to run it for about 6m - 8m. Is that ok?

Any assistance is greatly aprreciated

Rgds

from: http://www.usb.org/about/faq/ans5


Q1: How long of a cable can I use to connect my device?
A1: In practice, the USB specification limits the length of a cable between full speed devices to 5 meters (a little under 16 feet 5 inches). For a low speed device the limit is 3 meters (9 feet 10 inches).

Q2: Why can't I use a cable longer than 3 or 5m?
A2: USB's electrical design doesn't allow it. When USB was designed, a decision was made to handle the propagation of electromagnetic fields on USB data lines in a way that limited the maximum length of a USB cable to something in the range of 4m. This method has a number of advantages and, since USB is intended for a desktop environment, the range limitations were deemed acceptable.

thanks sflam good info..

Thanks sflam. It was most informative. TQ

izamjazz wrote:Hi,

Anyone out knows the maximum length of a usb cable from notebook to DAC can be before any reduction of signal sets in? I intend to run it for about 6m - 8m. Is that ok?

Any assistance is greatly aprreciated

Rgds

If the USB cable length exceeded its design capabilities, it will just quit working. Just like a HDMI cable.
You won't get a gradual degradation* unlike analog hifi connections, but it will happen as a step intermittent or total failure instead.

* for pure data connections, That is .

In practice, I have change from 5m usb to 3m, immediately notice the difference.

some have notice an improvement use Furutech, Wireworld, etc. Fancy ah.

I have posted before the jitters (eye diagram), can be seen at the digital section.

Am I correct to say; those exotic or more purposely built USB cable is tackling the EMI, RFI and Microphonics?, which indeed a major cause to the jitter problem?

But in that case, certain DAC has the ability to reclock the incoming data which tremendously reduce the jitter; instance like this the purposely built USB cable still make a change to final sound reproduction. Why?

Do you agree that EMI, RFI, and Microphonics are what is exactly the hi fi cable is dealing all these while? Are we being confused all the time just about the jitter, not the actual cause of the problem?

adrian4454,

the usb has a set of specifications. u can read all about it here http://www.usb.org/developers/usbfaq#13

just for an interesting read...

16. What does it mean when a product is USB compliant, and why should I care?

A: Compliance means products that are called USB products are really built to match the description in the USB specification. This is important to a customer because if all products match the spec perfectly they would by definition work together perfectly. The world is not perfect and so compliance testing exists to help manufacturers measure how well their products match the specification. There are many ways to make sure products work together and many ways to see if they match the specification, but compliance testing is one of the most useful. Conscientious manufacturers do a great deal of testing on their own and use compliance test programs like the one sponsored by our organization, USB-IF. If you don't find a product on our product list it does not mean there is anything wrong with that product, but if you do find it there you know that this manufacturer has put in a lot of effort to try to make sure that product matches the USB specification and has the best chance of working properly in a variety of applications. Please visit the www.usb.org/developers/compliance/ page for more details.

also, look at this q & a regarding ferrite beads to control emi.

4. What are the most common signal quality design mistakes?

A: Signal Quality is a mandatory test. See the signal quality test description for details. Most problems are the result of EMI "control" components like ferrite beads mounted on the signal lines. Often, these manage to destroy the integrity of the signal as well as make emissions worse.

it's not just about emi. rfi and microphonics. it's also about impedances. look at this:

6. What characteristic impedances should I design for in laying out my USB device's traces?

A: 30 ohms to ground, 90 ohms differential between the USB data lines. Be aware that many differential impedance formulas don't take into account the presence of a plane next to the data lines and tend to overestimate the reduction in single-ended impedance due to coupling between the two lines. For typical buried microstrips on spacings FR4 stackups the USB traces should be somewhere around 11 or 12mils wide with roughly a 33mil edge to edge spacing (45mils center to center). This is far enough apart that there's almost no coupling between the lines---the single-ended impedance is around 1.5O lower than what a single trace's impedance would be.

it's all very technical.

Thanks sflam. Anyway, does this spec being built into those industry standard USB cable? I've couple of this standard equipment USB cable, with many Industrial standard logo marked on the cable sleeve.

But I believe at the same time, those technical things being said inside the org isnt being built into those cable...

adrian4454,

it's true. there are lots of made-in-china usb cables that are below specs.

a friend passed me his hard drive for me to download a game. i used one usb cable that was lying around and the pc did not even recognise it.
the friend, who is an it expert, told me to use a different usb cable and it worked.
my friend said some of the cheap cables use too thin wires for the power supply cable and the resistance is too high for the usb outlet to power up the hard drive.

Hi Mr SF Lam,
I've been around Low Yat Plaza and obviously there's a plethora of USB cables of all sorts there. I'm in the market for some USB to mini USB cables for my media player and other purposes.
Any brand or types (with steetprices) with exceptional quality for audio or video media that you think are worth acquiring?
Possibly some reviews of good to exceptional cables you've used in the past? I'm just so afraid of those that "look nice on the outside, nice packaging but possibly poor in its actual build quality..thin weeny under spec wires that are camoflaged?". Can never trust whats offered nowadays.

If you need to run a long length of USB cable, you need a USB repeater. The distance between my computer to my printer is about 10m, so I run a USB repeater. It works just fine. It looks something like this: http://usbrepeater.com/

You should be able to find something similar at Low Yat Plaza.

on usb cables longer than five metres...

from http://www.usb.org/developers/usbfaq#cab2

2. I want to build a cable longer than 5 meters, why won't this work?

A: Even if you violated the spec, it literally wouldn't get you very far. Assuming worst-case delay times, a full speed device at the bottom of 5 hubs and cables has a timeout margin of 280ps. Reducing this margin to 0ps would only give you an extra 5cm, which is hardly worth the trouble.

3. What about using USB signal repeaters to make a cable longer than 5 meters?

A: Don't bother. The best solution is self-powered hub with a fixed 10m cable that had a one-port bus powered hub in the middle. The maximum range will still have to deal with the timeout, so any out of spec tweaking of the terminations between the two hubs and the timing budget still won't yield more than 5cm of extra distance. A better solution is described in the following question.

4. I really need to put a USB device more than 30 meters away from my PC. What should I do?

A: Build a USB bridge that acts as a USB device on one side and has a USB host controller at the other end. Use a long-haul signaling protocol like Ethernet or RS-485 in the middle. Using cables or short-haul fiber, you can get ranges upwards of a kilometer, though there's no reason why the long-haul link in the middle of the bridge couldn't be a pair of radio transceivers or satellite modems.
Embedded host solutions capable of doing this already exist. Also, two PCs connected via USB Ethernet adapters are essentially a slave/slave version of this master/slave bridge.

cmboy,
i use the usb cable that came with the benchmark dac1 pre. i hv yet to test the audiophile usb cables.