USB Cables and Digital Sound Quality

Lee · Jan 15, 2012

Recently via a dealer loan, I received an Audioquest Diamond USB 1.5 meter cable. I placed it between my Mac Mini running Snow Leopard and Decibel in HOG mode and my Benchmark DAC1 Pre. Previously I had a Belkin Gold USB cable.

The addition of the Diamond fleshed out the details, improved instrument separation and the soundstage increased in width and a little bit in depth.

Now I would have thought that the ones and zeros moving from the FLAC files on my Mac would arrive at the Benchmark fine either way.

Why am I hearing differences? By what mechanism does the sound change?

amirm · Jan 15, 2012

Well, the answer is that it is not 1s and 0s! There is no way to send perfect pulses on a cable. The waveform distorts and instead you get slanted ramps instead of perfect pulses. The receiver then attempts to recover the timing of the original pulses but it is not able to. To the extent your DAC then uses that clock to generate analog signal, the performance can change. Electrically it can also have an impact as far as what signal gets coupled form your source to the DAC.

That said, if you have an asynchronous DAC with electrical isolation, none of this should occur. I can't quite tell from the description of Benchmark DAC1 Pre what they do on USB. Seems that it is not asynchronous but what it is, I can't tell.

Vincent Kars · Jan 16, 2012

Benchmark USB is adaptive (24/96) , they use the Centrance implementation.

Lee · Jan 16, 2012

amirm said:
Well, the answer is that it is not 1s and 0s! There is no way to send perfect pulses on a cable. The waveform distorts and instead you get slanted ramps instead of perfect pulses. The receiver then attempts to recover the timing of the original pulses but it is not able to. To the extent your DAC then uses that clock to generate analog signal, the performance can change. Electrically it can also have an impact as far as what signal gets coupled form your source to the DAC.

That said, if you have an asynchronous DAC with electrical isolation, none of this should occur. I can't quite tell from the description of Benchmark DAC1 Pre what they do on USB. Seems that it is not asynchronous but what it is, I can't tell.

Amir, do you think that usb cables have different jitter characteristics that can cause sound differences? I know you have both DAC sampling jitter and there are transmission jitter as well.

rbbert · Jan 16, 2012

Does transmission jitter affect audio?

amirm · Jan 16, 2012

Lee said:
Amir, do you think that usb cables have different jitter characteristics that can cause sound differences? I know you have both DAC sampling jitter and there are transmission jitter as well.

That is the theory I was putting forward. We know that the cable changes USB jitter. To the extent some of that jitter leaks through to the DAC clock (and in adaptive mode it can), then that could impact the sound. Whether it is audible difference, is hard to say but it is also hard to rule it out due to this factor.

Phelonious Ponk · Jan 16, 2012

That said, if you have an asynchronous DAC with electrical isolation, none of this should occur.

Which, by the way, can be significantly less expensive than an Audioquest Diamond USB cable.

I don't know what you heard, but you don't have a problem to be solved by a usb cable more expensive than your Benchmark DAC. I assure you that Perter Aczel did not use an Audioquest cable, and he got stunning results from your DAC...

http://theaudiocritic.com/plog/index.php?op=ViewArticle&articleId=40&blogId=1

Tim

rbbert · Jan 16, 2012

It's still pretty hard to take Peter Aczel seriously...

And that cable is less than half the price of his DAC, not that that still isn't a bit crazy

amirm · Jan 16, 2012

Phelonious Ponk said:
Which, by the way, can be significantly less expensive than an Audioquest Diamond USB cable.

I don't know what you heard, but you don't have a problem to be solved by a usb cable more expensive than your Benchmark DAC. I assure you that Perter Aczel did not use an Audioquest cable, and he got stunning results from your DAC...

http://theaudiocritic.com/plog/index.php?op=ViewArticle&articleId=40&blogId=1

Tim

Those measurements do not apply to this situation Tim. There is nothing there relative to USB port and interactions with so many unknown PC configurations.

Lee · Jan 16, 2012

Amir,

I'm not convinced this is an "async or not" issue for one reason (besides a fairly robust Benchmark interface): a friend has the Ayre QB-9 which is async and we hear the same thing.

My bet is that some jitter can be transmitted by the cable even in async conditions but I could be wrong. I know there is such a thing as line induced jitter.

Lee · Jan 16, 2012

Phelonious Ponk said:
Which, by the way, can be significantly less expensive than an Audioquest Diamond USB cable.

I don't know what you heard, but you don't have a problem to be solved by a usb cable more expensive than your Benchmark DAC. I assure you that Perter Aczel did not use an Audioquest cable, and he got stunning results from your DAC...

http://theaudiocritic.com/plog/index.php?op=ViewArticle&articleId=40&blogId=1

Tim

Tim, the cable is $700 MSRP, the DAC1 Pre is $1,600.

No doubt the cable is pricey nonetheless.

amirm · Jan 16, 2012

Lee said:
Amir,

I'm not convinced this is an "async or not" issue for one reason (besides a fairly robust Benchmark interface): a friend has the Ayre QB-9 which is async and we hear the same thing.

As I noted, electrical coupling is the other source of interference and it is hard to know how well devices isolate relative to the myriads of PC configs.

My bet is that some jitter can be transmitted by the cable even in async conditions but I could be wrong. I know there is such a thing as line induced jitter.

Line induced jitter is what I have been describing

. The issue is that in async mode, it should have no effect because the clock that feeds the DAC, runs independent of it. Where it is not independent is in electrical coupling that could impact the DAC clock still.

There is an easy way to verify this which sadly no one does. Jitter can be measured. So if there is an effect, we could document it yet seems like this data is never presented. For that reason, I think we have to allow for possibility of this being placebo

.

Lee · Jan 16, 2012

Thanks Amir.

The electrical coupling comment resonates since I have noticed that better ac cords seem to make a real nice difference on DACs and CD players in my experience.

I'm not sure why line induced jitter has not been measured. I contacted Gordon Rankin to see if he has any thoughts.

DonH50 · Jan 16, 2012

Could someone please define "line induced jitter" for me? I can list a number of reasons a cable might contribute to jitter, but before spouting off want to see where I stand (must be getting cautious in my old age).

BTW, measuring jitter is hard and takes some pricey equipment, probably partial reasons it is seen so infrequently in reviews and specs.

Lee · Jan 16, 2012

DonH50 said:
Could someone please define "line induced jitter" for me? I can list a number of reasons a cable might contribute to jitter, but before spouting off want to see where I stand (must be getting cautious in my old age).

BTW, measuring jitter is hard and takes some pricey equipment, probably partial reasons it is seen so infrequently in reviews and specs.

Hi Don, my brother lives in Monument. Great place. Look at this article: http://www.nanophon.com/audio/jitter92.pdf

DonH50 · Jan 16, 2012

Cool, we should try to hook up sometime!

Thank you for the link. The article (in my 2-second look) appears to define line-induced jitter as due to bandlimiting. I would certainly say that is by far the largest factor, but there are many others. However, I strongly suspect the other factors are in the mud for audio links. My guess for audio line-induced jitter causes would be (a) bandlimiting, (b) loss from long lines, (c) poor shielding leading to EMI issues, and (d) everything else at a much lower level.

On the coupling issue, I have a vague memory of an article discussing HDMI or USB links and discovering one of the benefits of a more expensive cable was the much better shield and heavier ground on the more expensive cables. However, for USB links, I still think galvanic isolation is the way to go.

Phelonious Ponk · Jan 16, 2012

It's still pretty hard to take Peter Aczel seriously...

Exactly the way I feel about most audiophile reviewers.

Tim

amirm · Jan 16, 2012

DonH50 said:
Could someone please define "line induced jitter" for me?

Simplest and best explanation is done in Jullian Dunn's tutorial for measurement of digital audio using Audio Precision analyzer. I have references this useful chart from him:

He also has practical measurements of cables in a recommendation doc he created for AES.

The above was done using an audio cable for AES interconnect and a long one at that. The actual doc is in our library section of the forum.

BTW, measuring jitter is hard and takes some pricey equipment, probably partial reasons it is seen so infrequently in reviews and specs.

I would think they can rent the gear and or have a lab make the measurement for them. Seems like the stuff sells without it so they don't bother.

Vincent Kars · Jan 16, 2012

Has anybody read the article in Hi-Fi news (January 2011)?
Paul Miller has tested a couple of USB cables and on a forum somebody said that he found out an audiophile cable being much worse in jitter performance than an ordinary one.
I’m afraid the article is not online.
Time to ask Paul Miller to join WBF!

amirm · Jan 16, 2012

I wouldn't be surprised these guys are shooting blind in changing cables and not knowing without measurements, whether they have moved forward or back. Orb mentioned the same regarding Paul's tests: http://www.whatsbestforum.com/showt...yond-say-10-feet&p=53850&viewfull=1#post53850

In fairness, whether a cable makes a difference or not is source dependent. So Paul's tests can't be representative of all situations.

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