USB cable..difference are they measurable? An experimental model

[awsmone]

Dear all

I have been pondering putting some of these controversies on a scientific footing

Surely, since usb cabling involves transmission of digital data, this can be analysed.

My understanding is the proposition by cable manufacturers is that there are three areas more expensive usb cable is superior

1. lower data transmission errors
2. lower noise floor... polluting the DACs noise floor etc
3. greater immunity to RF....polluting data error and noise floor

If these are the case surely we can measure these?

In recording industry data errors can be measured

Noise floor should also be measurable

And different cable immunity to RF interference also

Surely this can be done between expensive and stock cable ?

The scientific null hypothesis is there will be no difference

My personal suspicion is the results will be

1. data: no difference in error rates
2. noise: maybe but won't effect data error rates
3. rf : yes, won't effect data error, might effect noise

I have not fixed view on the results, and be more than happy to be proved wrong

However, results might help/ it could help inform discussions ?

 

[Folsom]

rf is noise...

Streaming data has higher rates of loss because it can be buffered and checked.

Noise affects whatever it feeds. It's cumulative so even if it adds little, it adds. But consider it's directly adding noise to something that converts to streaming. Hence noise is very bad to have at this critical point.

The biggest problem with USB cables is the noisy power leg on them, that's why there's many alternatives to straight power from the source.

Best advise? Check with ears. Many have been surprised.

 

[awsmone]

ah sorry but i am not talking about streaming but difference in usb cable

and i am not talking about audible differences but measurable

 

[Folsom]

USB cables can be used for streaming data. But also as I stated whether or not the USB is, it has an effect on things that do so considerable care about the noise on the USB cable matters.

I'm trying to help you understand what measurements and why you'd want them since you're just learning on the subject.

You know, you have to choose what cables to measure, ya?

 

[awsmone]

Seriously

where talking about setting up a experimental method

the test subject is are difference in usb cables real: from a measurement viewpoint not audible

please address the issue?

the way they r used re: streaming is irrelevant

noise is one of the parameters i have said should be measured

rf immunity is another...its effect on noise is obvious?

i honestly don't understand your point?

as the three parameters i have mentioned to be tested you have simply reiterated ?

 

[Folsom]

I am. You need to know what to measure and why.

I'll setup some scenarios based on what I've said.

1. Measure the cables ability to reject noise from source, by measuring source.

2. You'll need a noise generator that to see what it can pick up from air. I'd prefer something that can do a wide range, 60hz and 5-200mhz especially.

3. Separate PSU for USB, as clean as possible. A transformer would be good too. Measure effect of noise with and without USB power from dirty source (computer), both types (computer/clean)

4. Repeat all tests with streaming and pulse to check for data loss.

 

[Folsom]

And again, rf is noise unless you're using a tuner. What you must be trying to say is the different things I pointed to measure, from air or from source. Either could be any range of noise, any frequency, RF or not. All of which are noise.

 

[LarsS]

Starting point could be measuring cables electrical performance and adherence to USB spec, something like Supra publishes on their cable:

Electrical performance
Resistance: 72 (Ohm/km)
C: 52 (pF/m)
Imp. Z: 90 Ohm
Velo. Factor 0.66c

 

[Vincent Kars]

As it is about “digital” cables, try measuring the eye-pattern.
If I remember correctly HiFi-news did so a couple of years ago and found differences between cables.

 

[DonH50]

Even the eyes might not tell much since so much depends upon the receiver... A good receiver can recover data without error from a nearly or completely closed eye.

One of the oft-mentioned and yet still overlooked issues with USB cables is the ground path. Connecting the DAC to the PC ground can add common-mode noise the DAC may or may not be able to adequately reject.

 

[thedudeabides]

Shouldn't this thread be in the Measurement Based Forum?

Given its title, I think so.

That's why it was created.

 

[amirm]

Shouldn't this thread be in the Measurement Based Forum?

Given its title, I think so.

That's why it was created.

It should be especially the way OP has positioned the question, i.e. measurement vs audibility.

 

[amirm]

Answering here for now, the measurements listed can easily be done. Unfortunately the signals traverse at high enough bandwidth (i.e. rise time), that requires a very expensive scope and specialized input probe.

 

[thedudeabides]

It should be especially the way OP has positioned the question, i.e. measurement vs audibility.

Don't you have the ability to move it to the appropriate forum?

I, for one, am glad you all created the measurement forum. A very pro active move to try to reduce the "friction" between the O and S crowd.

 

[amirm]

Don't you have the ability to move it to the appropriate forum?

Not any more. I am demoted to an ordinary user (see my title).

I, for one, am glad you all created the measurement forum. A very pro active move to try to reduce the "friction" between the O and S crowd.

That was the hope.