A USB Cable Test Designed to Satisfy Skeptics AND Believers—Feedback Welcome

[BeeKay]

For example, when I download photos from my camera, the colors are more vibrant with a certain USB cable.

Interesting. Same as with the audiophile SATA cable. I had trouble as my Excel files started to become more analog, less analytical when I accidentally stored some on the audio drive. Wasn’t helpful.

 

[Guestuser]

Having done dozens of tests on USB cables, including ones designed for experimenting with shields and geometry, I found there was sometimes a measurable difference between cables in the noise floor, but normally below any thresholds of hearing. And yes, I've done multiple blind tests on USB cables, as well, although obviously the results can't be generalized to anyone else.

The problem with induced noise null hypothesis is that it depends on too many variables, including ambient EMF noise levels and spectrum, specific DAC or device topology and design, grounding scheme, and what other circuits are connected beside the USB cable.

If you're really concerned with induced noise, use a USB galvanic isolator that will not let through any of the induced noise. These are available for under $30 and are extremely effective. I use such devices in all my measurements, as it eliminates one source of error that is external to the device I'm measuring.

In my own system, I have an Intona 7055-C usb isolator with a separate LPS, so can appreciate this comment. Any suggestions for how to incorporate a USB isolator into the test? The cable to be tested should go between the isolator and the DAC?

 

[voodooless]

I’m puzzled by all of the expressions of futility and pointlessness here in response to the idea of rigorous and well-designed tests with the potential to expose and embarrass the audiophile claims of people currently hunkered down in the fog bank of unchallenged subjectivity.

Apathy and bare-ass cynicism are not scientific values.

This isn’t about the test itself. The question is if this is the best instrument to reach the goal: reach those hunkered down audiophiles.

And here the science is clear: studies and data will not convince these people.

 

[pkane]

In my own system, I have an Intona 7055-C usb isolator with a separate LPS, so can appreciate this comment. Any suggestions for how to incorporate a USB isolator into the test? The cable to be tested should go between the isolator and the DAC?

You want a very short cable from the isolator to the DAC, and a very long cable leading into the isolator. For best effect, wrap the long USB cable around a transformer or some other emitter of a large EMF. Test with isolator in and out of the circuit, and the transformer on or off.

 

[Guestuser]

You want a very short cable from the isolator to the DAC, and a very long cable leading into the isolator. For best effect, wrap the long USB cable around a transformer or some other emitter of a large EMF. Test with isolator in and out of the circuit, and the transformer on or off.

Maybe something like this Bulk Current Injection (BCI) clamp could be used? https://www.avalontest.com/teseq-cip-9136a-bulk-current-injection-test-clamp

 

[MCH]

In my own system, I have an Intona 7055-C usb isolator with a separate LPS, so can appreciate this comment.

400 eur! From a company that sells that, and 300 eur USB cables.... ouch!

 

[HalSF]

This isn’t about the test itself. The question is if this is the best instrument to reach the goal: reach those hunkered down audiophiles.

And here the science is clear: studies and data will not convince these people.

I just had some back-and-forth at another forum with some confirmed adherents of pricey audiophile USB cables and the lower noise floor and added smoothness, resolution, and “$10K DAC” leap in sound quality they attribute to these cables vs. ordinary well-made in-spec cables. It would be useful to have evidence of the consistent replication of failure to reliably distinguish between audiophile and generic cables via blind testing. Even if such evidence has already been rigorously produced I’d like to see more. I don’t care if the “not everything that matters can be measured” cult ignores it.

 

[krabapple]

I'm reading that spending by the wealthy (plus floods of money being spent on AI infrastructure) is currently all that's keeping the US economy afloat.
So we Americans had best encourage idiots with money to keep buying these pricey audiophile trinkets.

 

[Salida]

When I was designing broadcast signal processing equipment for a living I did a bunch of ABX testing with a David Clark DLC designs ABX tester and an end-to-end broadcast chain.

Even with moderate differences in processing methodologies experienced listeners were often hard pressed to determine an A B preference using program material, resulting in frequent null outcomes.

I think you are interested in designing an experiment that will prove or disprove the following two hypothesis:

Unlike other USB protocols, Asynchronous Isochronous USB (UAC2) does not have any error detection and correction built in. Therefore the potential exists for undetected data errors to be passed to the DAC. Are USB cables creating errors that are detectable in controlled listening tests?

The USB receiver is powered by the sending device and is not galvanically isolated. USB cables also vary in their physical construction and EMI coupling. Therefore the potential exists for noise on the USB transmitter’s power and ground lines to be coupled into the audio system DAC ground and power supplies. Under what conditions does this become audible?

The first hypothesis is easy to prove using data transmission testing methodologies, so is less interesting than the latter.

The USB noise hypothesis inherently has a large number of variables that would need to be controlled. USB transmitter power supply design, host computer prior supply design, USB receiver design, DAC design, other connected equipment, etc. You could prove something about a specific instantiation but it would be difficult to expand that to other scenarios.

 

[Guestuser]

When I was designing broadcast signal processing equipment for a living I did a bunch of ABX testing with a David Clark DLC designs ABX tester and an end-to-end broadcast chain.

Even with moderate differences in processing methodologies experienced listeners were often hard pressed to determine an A B preference using program material, resulting in frequent null outcomes.

I think you are interested in designing an experiment that will prove or disprove the following two hypothesis:

Unlike other USB protocols, Asynchronous Isochronous USB (UAC2) does not have any error detection and correction built in. Therefore the potential exists for undetected data errors to be passed to the DAC. Are USB cables creating errors that are detectable in controlled listening tests?

The USB receiver is powered by the sending device and is not galvanically isolated. USB cables also vary in their physical construction and EMI coupling. Therefore the potential exists for noise on the USB transmitter’s power and ground lines to be coupled into the audio system DAC ground and power supplies. Under what conditions does this become audible?

The first hypothesis is easy to prove using data transmission testing methodologies, so is less interesting than the latter.

The USB noise hypothesis inherently has a large number of variables that would need to be controlled. USB transmitter power supply design, host computer prior supply design, USB receiver design, DAC design, other connected equipment, etc. You could prove something about a specific instantiation but it would be difficult to expand that to other scenarios.

Thanks for sharing your experience and ideas. The protocol includes a bus-powered DAC with no isolation as well as a DAC with its own power supply and isolation controls.

Someone else suggested similar feedback about controlling for interference and I agree that should be included. Current thinking is to use a USB isolator between the audio source and DAC. Then place the test cable between the isolator and the DAC with an interference injection clamp on the test cable. The injection clamp would allow for a controlled amount of interference and ensure the interference is focused on the cable and not directly impacting the DAC. Of course, the interference on the cable could bleed to the DAC, but that’s the point of the test.

 

[mhardy6647]

For example, when I download photos from my camera, the colors are more vibrant with a certain USB cable.

Does that difference fade after a while if you don't transfer 'em back and forth through that same cable now and again?
Asking for a friend.


EDIT:
PS What I am really waiting for are Kimber Cable directional USB-C to USB-C audiophile cables. That arrow will be all-important!

 

[RandomEar]

Some people believe USB cables transmit only binary digital data (0s and 1s), and others assert that USB cables can still affect the output stage of a DAC (antenna effect, etc.). This test is designed to control for both scenarios by using shielded and unshielded cables, as well as two different DACs: one bus-powered DAC with no galvanic or chassis isolation, and another DAC with a separate power supply, galvanic isolation, and chassis isolation. If there is no effect with any combination of cables and DACs, the "digital only" part of the debate will now have data to support or disprove it.

Edit: The problem with audio analysis of the DAC output using an audio analyzer is that the analyzers themselves are extremely shielded and resilient against RFI/EMI interference. The objections I've seen are that not all DACs have this type of shielding, and therefore, the antenna effect could affect the DAC output stage regardless of whether the data stream is stable. This protocol directly addresses that objection by including a bus-powered DAC with no shielding.

Again: If it's only about noise (and that antenna effect is exactly that), you can just capture that with an ADC like an ADI 2 FS Pro. I don't understand what any shielding of that ADC would do to the input signal noise. The ADC captures what the DAC outputs, so it effectively replaces the amp in the playback chain. If the DAC is "affected" by that noise, it will be present at the DAC outputs and will be captured by the ADC.

Differences in the grounding scheme of the whole setup including the ADC will affect ground loops and noise, but that problem will also affect any real system with an amp.

If it is only about noise, you could also simply play a silent track and then listen for or record the noise using a microphone, if you insist on an air gap. There is no need for playing music and complex double blind testing if you just want to determine if any EMI induced noise is present in the DAC output.

@Salida is correct that the USB audio protocol lacks error correction. However, in my experience, bit errors in audio transmission are not subtle. If you ever listened to a portable CD player with an undersized playback buffer or tinkered with individual samples in Audacity, you will remember how jarring such tiny errors can sound

 

[Mr. Swordfish]

Nothing will end the cable debate, no point trying. Usb is a digital protocol, its either broken or working, theres no in-between.

Sometimes problems are intermittent. Works for a while, then flakes out, then works again. So there is an "in-between"

Yeah, in the digital world there are redundancies and error corrections that mitigate or remove the intermittent problems, but a sufficiently poorly made cable could at least in theory appear to work while degrading the audio via short dropouts.

But I'd need to see evidence of this actually happening. Should be easier to measure than hear.

 

[Guestuser]

Again: If it's only about noise (and that antenna effect is exactly that), you can just capture that with an ADC like an ADI 2 FS Pro. I don't understand what any shielding of that ADC would do to the input signal noise. The ADC captures what the DAC outputs, so it effectively replaces the amp in the playback chain. If the DAC is "affected" by that noise, it will be present at the DAC outputs and will be captured by the ADC.

Differences in the grounding scheme of the whole setup including the ADC will affect ground loops and noise, but that problem will also affect any real system with an amp.

If it is only about noise, you could also simply play a silent track and then listen for or record the noise using a microphone, if you insist on an air gap. There is no need for playing music and complex double blind testing if you just want to determine if any EMI induced noise is present in the DAC output.

@Salida is correct that the USB audio protocol lacks error correction. However, in my experience, bit errors in audio transmission are not subtle. If you ever listened to a portable CD player with an undersized playback buffer or tinkered with individual samples in Audacity, you will remember how jarring such tiny errors can sound

This protocol’s primary evidence is perceptual and the null test measurements are included (section 5.3.3) but they supplementary. This would allow us to verifiably distinguish the degree of measurable vs audible differences.

 

[amirm]

However, in my experience, bit errors in audio transmission are not subtle.

Indeed. Years ago I tested a "USB Regen" device that claimed to cleaned up USB. To test that, I created a very long and thin USB cable out of a number of individual cables. It took a bunch of them to induce errors. But I got there and turns out the USB Regen had a lousier receiver than a cheap USB hub! I captured the output when the USB Regen was in the loop:

Dropbox

www.dropbox.com

We hear clear static. And of course it is readily measurable:

 

[Sir Sanders Zingmore]

Perhaps I’m about to confirm my biases by saying this but I suspect that that this would actually end up being yet another test of confirmation bias

 

[Guestuser]

Perhaps I’m about to confirm my biases by saying this but I suspect that that this would actually end up being yet another test of confirmation bias.

You might be right about how people react to results but the protocol itself is specifically designed to limit confirmation bias in the data.

Could someone still dismiss results they don’t like? Sure. But they’d have to argue the blinding failed, the placebo controls don’t count, and the validation was a fluke. All of that while the analysis plan is open to public comment before data collection.

 

[RexrothPigeon]

I’m puzzled by all of the expressions of futility and pointlessness here in response to the idea of rigorous and well-designed tests with the potential to expose and embarrass the audiophile claims of people currently hunkered down in the fog bank of unchallenged subjectivity.

Apathy and bare-ass cynicism are not scientific values.

I can't speak for anyone else, but I am not opposed to the OP carrying out these tests. The tests have no value to me, and won't persuade the true audiophoolery die-hards, of course, and I'd rather see all this time and effort (and money) put to study something that isn't already scientifically "settled," but if the OP wants to do this study its their time and effort and money wasted not mine.

I don't think that's what's happening here, though. Correct me if I'm wrong, but this looks like an experiment design with no provision (or budget) for actual execution.

 

[solderdude]

If you can't measure a difference, you certainly can't hear one either.

Still possible to hear a difference even when there isn't any.
That's the magic of perception.

 

[somebodyelse]

Unlike other USB protocols, Asynchronous Isochronous USB (UAC2) does not have any error detection and correction built in. Therefore the potential exists for undetected data errors to be passed to the DAC. Are USB cables creating errors that are detectable in controlled listening tests?

Before determining whether the errors are audible we can determine experimentally whether they exist at all in the received data. If none exist then there's no need to test whether it would be audible. One easy way may be to use one of the RME DACs that report on bit perfect reception of a test signal. Another would be with some custom XMOS firmware based on their example UAC2 receiving code but reporting data received and any detectable errors. That gets around the argument that a USB debugger is somehow different from the USB receiver in a DAC since so many use XMOS and code not much different from the examples.