Do USB Audio Cables Make A Difference?

[watchnerd]

I find B to C printer cables give great value for money with wonderfully transparent results.

 

[SIY]

I find B to C printer cables give great value for money with wonderfully transparent results.

Only if you print on Mylar.

 

[Kane1972]

I bought a "hi fi" USB cable that was not expensive, but not cheap (about £20 I think). However, it uses 2 USB ports from the computer and takes power from one port and data from the other. I have no idea if this does actually result in any real benefit, but would be great if you could test such a cable. It is only about 200mm long as well.

 

[mansr]

I bought a "hi fi" USB cable that was not expensive, but not cheap (about £20 I think). However, it uses 2 USB ports from the computer and takes power from one port and data from the other. I have no idea if this does actually result in any real benefit

It results in violating the USB spec. Maybe some see that as a benefit.

 

[Forman]

I bought a "hi fi" USB cable that was not expensive, but not cheap (about £20 I think). However, it uses 2 USB ports from the computer and takes power from one port and data from the other. I have no idea if this does actually result in any real benefit, but would be great if you could test such a cable. It is only about 200mm long as well.

They suggest that you power your DAC from a power bank. If you have a self powered DAC you can disconnect the USB connector that carries the +5v power after the initial handshake.

I bet most cables still have the USB-spec shielding intact, meaning there is still a possibility for ground loops and noise. The cable shield is connectoed to ground on both sides.
And the powerbank recommendation might not be so smart. Handy when you need to charge your phone, but none of the ones I have seen are even remotely suited for low noise applications. The boost converter used to generate the 5v output are even more noisy than the buck converters used in the computer. Proper filters are usually abandoned to keep size and costs down.

 

[Kane1972]

OK, so the one I have is made by Achtung Audio, which i belive now goes by the name Gothic Audio. The one I have now sells for £50, which i'm sure I didn't pay that much. Only difference is mine does not have the gold plated ends that they have now. Like I say, I have no idea if splitting the power from the data is an improvement or not, which is why I think it would be great if Amir could test it.

 

[DeepSpace57]

what do you think about this? AQ pearl is another option.

 

[pkane]

Here's a USB cable comparison showing some differences

Lush2 audiophile USB cable vs. a generic (came with one of the non-audio USB devices). Lush2 has some jumpers to allow for various shield/ground combinations. It was used in stock configuration, as shipped. Red is Lush2, blue is generic cable:

The test was using Holo Spring DAC in NOS configuration, 100Hz sine wave captured using Apogee Element 24 at 24/96k. Nothing was moved or touched between the tests, other than switching USB cables. I switched them a few times to see that the pattern is repeated.

How does Lush2 USB cable cause higher level harmonics around 4kHz is hard for me to explain, although these are low enough in level. The 60Hz mains frequency component is obviously there only when using Lush, so the default shielding configuration seems to be not as good as the generic USB cable. The generic does have a built-in ferrite bead near both ends. Lush is 0.75m and generic is 1m in length.

 

[DeepSpace57]

Here's a USB cable comparison showing some differences

Lush2 audiophile USB cable vs. a generic (came with one of the non-audio USB devices). Lush2 has some jumpers to allow for various shield/ground combinations. It was used in stock configuration, as shipped. Red is Lush2, blue is generic cable:

View attachment 31828

The test was using Holo Spring DAC in NOS configuration, 100Hz sine wave captured using Apogee Element 24 at 24/96k. Nothing was moved or touched between the tests, other than switching USB cables. I switched them a few times to see that the pattern is repeated.

How does Lush2 USB cable cause higher level harmonics around 4kHz is hard for me to explain, although these are low enough in level. The 60Hz mains frequency component is obviously there only when using Lush, so the default shielding configuration seems to be not as good as the generic USB cable. The generic does have a built-in ferrite bead near both ends. Lush is 0.75m and generic is 1m in length.

So, although lush is shorter, generic cable costing 200 euros less is better.

 

[pkane]

So, although lush is shorter, generic cable costing 200 euros less is better.

It would seem that way. I'll need to try all the other 200+ shield/jumper configurations on Lush2 before I can legitimately make this conclusion

 

[pkane]

Here's a USB cable comparison showing some differences

Lush2 audiophile USB cable vs. a generic (came with one of the non-audio USB devices). Lush2 has some jumpers to allow for various shield/ground combinations. It was used in stock configuration, as shipped. Red is Lush2, blue is generic cable:

View attachment 31828

The test was using Holo Spring DAC in NOS configuration, 100Hz sine wave captured using Apogee Element 24 at 24/96k. Nothing was moved or touched between the tests, other than switching USB cables. I switched them a few times to see that the pattern is repeated.

How does Lush2 USB cable cause higher level harmonics around 4kHz is hard for me to explain, although these are low enough in level. The 60Hz mains frequency component is obviously there only when using Lush, so the default shielding configuration seems to be not as good as the generic USB cable. The generic does have a built-in ferrite bead near both ends. Lush is 0.75m and generic is 1m in length.

Now a null comparison between a 24/44.1k original digital file and captured audio. This also shows a small difference, again the generic cable comes on top compared to Lush^2. Interestingly, there is a small level difference (0.2dB), likely due to a bit higher harmonic distortion with Lush.

First, generic USB nulled with original digital file (-65dB rms null and 67dB correlated null):

And Lush2 null with original file (-62dB rms and 64dB correlated nulls):

Spectrum of the null (delta) between the original file and generic USB cable ADC capture:

And between original file and Lush^2 capture:

 

[scott wurcer]

I wish sometimes that folks would realize how absurd the concept is that a digital cable by its materials or construction could rearrange bits in a data stream to create, for instance, harmonic distortion or consistent frequency response deviations in the decoded digital data.

 

[pkane]

I wish sometimes that folks would realize how absurd the concept is that a digital cable by its materials or construction could rearrange bits in a data stream to create, for instance, harmonic distortion or consistent frequency response deviations in the decoded digital data.

I'm with you, bits are not rearranged or molested in any way. Except there are some differences in what I measured above and here. So, what explains these? The original post by Amir also shows measurable differences between USB cables at the DAC output.

Is it EMI/RFI? Ground problems? 5v power-line noise? something else?

 

[graz_lag]

I wish sometimes that folks would realize how absurd the concept is that a digital cable by its materials or construction could rearrange bits in a data stream to create, for instance, harmonic distortion or consistent frequency response deviations in the decoded digital data.

I do not know abt. frequency or harmonic distortion, I know abt. noise:
Picture transferred from my Pentax K-1 via my esoteric audio-homeopathic USB-cable ...



The same now by means of my cheaply 1999 USB-printer cable, Canon branded though ...

 

[SIY]

Is it EMI/RFI? Ground problems? 5v power-line noise? something else?

This is begging for a gauge R&R.

 

[pkane]

This is begging for a gauge R&R.

I ran three tests against each cable. I'll do another set another night, just to be sure it wasn't an unexpected lunar eclipse or a sunspot causing this

 

[Kane1972]

I believe cable induced jitter is a thing in coaxial digital cables, not so sure about USB though? I think electrical noise can also make error correctors work incorrectly, so may be cables can help keep out some of that?

 

[SIY]

I ran three tests against each cable. I'll do another set another night, just to be sure it wasn't an unexpected lunar eclipse or a sunspot causing this

Probably telling you what you already know but... between runs, unplug the cables, shut down source and receivers, restart source and receivers, replug cables.

 

[Kane1972]

Here is an interesting old post from "Mal" on another forum about cable induced jitter. Not sure if USB audio is the same though?

Lets take a look at the timing issue - according to the theory of digital transmmission of analogue signals, in order to reproduce the original analogue signal perfectly samples are supposed to be spearated by exactly 1/f seconds where f is the sampling rate in Hz. Now, in the real world no system can be designed to present samples at an absolutely exact interval. So, there will be an error in the timing of each sample - that is a simple fact. As long as we can design sytems where this error is low enough for the data to still be transmitted intact then we at least have a working sytem. However, unless the samples are perfectly timed the resulting reconstructed analogue waveform will not be a perfect replica of the originally encoded one.

When you send a digital signal down a cable then the waveform you get out at the other end doesn't look the same. The digital signal is a series of pulses:

It is impossible to generate the pulses such that they have a perfrectly vertical rise and then a right-angle at the top and then a perfectly vertical drop since those instantaneous changes in amplitude represent infinite frequency. Rather, you will have a slightly rounded looking version of these pulses.

Once you send these down any length of cable then they will be further changed due energy loss. Any cable will have a transmission function which tells you how well is passes different frequencies. No cable can pass infinite frequency - most can't even pass more than a few MHz. If you are wondering why for digital transmission plastic TOSLINK, despite being able to pass 30MHz is not considered as good as glass which can pass 60MHz or more then the answer lies in how accurately it is delivering the pulse train. The lower the rated frequency capability then the more rounded the signal becomes.

Furthermore, other distortions occur to the pulse train due to reflections, electrical interference (in the case of metal cables) etc....

Now, in order to reconstruct the data transmitted by the cable all we need to know is where the 1's and 0's are so it may be tempting to assume that as long as you can still recognise the pulse train however rounded the corners have become and however distorted they may have become then you are still in business. The problem is that once the pulse no longer looks like it did originally it is no longer as easy to define where it is in time. In the original signal you could say that the beginning of each pulse is the sample timing reference point. However, once that has been rounded off where do you set the reference point? Maybe we could choose the middle of the pulse? Well, again once the corners have been rounded off and the general shape of each pulse is distorted by random effects such as electrical inteference then you can no longer define the timing of sample points so accurately.

Now, since many DACs derive their clock signal from the incoming data stream this is clearly going to affect the resultant analogue output.

Whether the effects of these time-based errors (ie jitter) on the reconstructed analogue output will be audible is a matter for debate but the fact that these errors exist is a simple fact of digital audio.

 

[pkane]

I believe cable induced jitter is a thing in coaxial digital cables, not so sure about USB though? I think electrical noise can also make error correctors work incorrectly, so may be cables can help keep out some of that?

Noise is likely the problem. Jitter on SPDIF can affect the output timing directly, since the clock is derived from the SPDIF stream. USB data is sent in packets and stored in memory before being clocked out using an independent oscillator. Jitter within USB spec should have no effect on DAC output.