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USB A->B cable - max length without lowering signal quality or adding jitter in DAC?

ethanhallbeyer

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So I have a PC on a rack in a little rack cabinet that is on the other side of my room. On the other side, I have my monitor, keyboard, mouse, amp, DAC and speakers. I have found an active DP cable that will be long enough to run from the rack cabinet to my monitor on the other side of the room. My keyboard and mouse can use usb extension cables w/o issue and I'm not concerned about performance degradation there.

The only other cable I need is an extension cable for USB A->B, so that I can connect from the rack cabinet PC to my DAC on the other side of the room. I'm guessing I need about 25' length. I've seen active USB cables available at that length. My question is would that compromise audio quality/signal or increase jitter when used between an external DAC and PC? if so, I will have to likely find another solution.
 

mansr

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The maximum length for a USB2.0 compatible cable is about 5 m or 16 feet. Longer cables exist, but these are by definition not spec compliant and thus cannot be guaranteed to work with every device. If too long a cable is used with a DAC, you will have dropouts or it may fail to be recognised at all. You will not get any subtle degradation of sound quality, so if it works, there's no need to worry.
 

RayDunzl

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I'm guessing I need about 25' length. I've seen active USB cables available at that length. My question is would that compromise audio quality/signal or increase jitter when used between an external DAC and PC?

I've used this one for six years without any issues.

https://www.amazon.com/Tripp-Lite-H...ocphy=9012086&hvtargid=pla-309291855031&psc=1

Wow, it's $2 less now.

---

Also one of these, more recently, but it is less reliable. Has limits on the power transfer for devices it must power.

https://www.amazon.com/gp/product/B074JJ3YFY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I'm using it now to feed data to a powered hub at the rack.

It seems to be fully capable of that. The hub has four devices plugged into it.
 
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ethanhallbeyer

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Thanks for your replies! I was just worried about added jitter or degraded sound quality. I am using PC as source and with USB out to a balanced DAC then to balanced AMP direct to my speakers, so I didn't want to degraded the signal/quality. Seems like the triplite cable linked to above may do the trick for me.
 

RayDunzl

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I now note the TripLite has a power delivery limitation of 150ma.

Therefore, neither cable is particularly well suited to operate devices that draw power from the USB.

Also, the cheapie cable is an extender Type A connector on both ends - the TripLite has a B connector on one end.
 

amirm

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Don't worry about jitter. It is not a concern in that regard. When the extension cable doesn't work right, you will hear clear static/pops. So get a cable from Amazon, etc. that you can return to test. Some devices are better at receiving end than others so hard to predict what will or will not work.
 

enioentity

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Don't worry about jitter. It is not a concern in that regard. When the extension cable doesn't work right, you will hear clear static/pops. So get a cable from Amazon, etc. that you can return to test. Some devices are better at receiving end than others so hard to predict what will or will not work.

There is a guy here, he ran some tests and there are some errors that show up on longer usb cables. Not sure if those matter or not..

Here is what he wrote:


I used a Lecroy Mercury T2 USB protocol analyzer to measure errors. I used several sources:

Deskside computer, homebuilt, Supermicro motherboard, Xeon processor, 32 gigs memory Windows7 64bit. Foobar 2000 playing local files.



LenovoT460S laptop, powered from provided SMPS and also tried from internal batteries. Also running Win7 64bit. Foobar 2000 playing local files.



Sonore ultraRendu in squeezelite mode over LAN from vortexbox software running on compulab fitlet.



DACs:

Soekris dac1101

micca OriGen+

Bottlehead Dac



Cables:

whatever I had on hand. This was NOT designed to be a test of specific brands, I didn't buy any cables for this test. There were only three cables that had a brand name, Supra, Belkin and EVERNEW. The rest did not have brand names but did usually have some form of USB 2.0, usually a temperature max etc. The Supra and Belkin were the only ones I bought specifically as a cable purchase, the others came with DACs and other stuff bought over the years.



Error rates:

Under 6ft, no errors with any cable, source DAC combinations.

6 to 10ft, all source and DAC combos, except for Supra cable. Occasional errors, somewhere between 1 error every several minutes to 1 error every seconds. Different source and DAC combinations made very little difference. It was hard to give precise error rates. Even with exactly the same setup error rates varied quite a bit. I tried different times of day, different room temperatures and couldn't find any decent correlations. Sometimes it would go for ten minutes without an error, then have a whole bunch of errors within 10 seconds. The Supra in this range didn't have any errors, but all the others behaved pretty much the same, they all varied a lot between minutes per error to groups of errors close together.



Above 10ft ALL the cables had errors. This is where I saw some differentiation between cables and equipment combinations. A few combinations had many errors per second which caused the DACs to drop the connection. Withe the same source and DAC changing cables did make significant differences. They all had errors but some would be at 1 per second and others would be at 10-20 per second. At this length sources did make a difference but the DAC made a much bigger difference. One of the DACs would stay connected even if getting lots of errors but the other two would disconnect when the error rates got above 2 errors per second.



As a separate test, quite a while after the original, I DID measure a corning optical cable, 30ft long, this worked very well, no errors under any combination.



Note this was NOT a test designed to measure specific brand cables. I really had no idea what error rates existed on music over USB cables so I decided to test systems using equipment and cables I had on hand, that is all this test was about, there was no sound quality part of this test, it was all about errors as detected by the analyzer. It was not supposed to be any form of uniform representation of the entire universe of cables.



Summary of results: Note this is for the cables and equipment I had on hand others may be different.

Cable length DOES matter. Under 6ft no errors with any cables and equipment combinations.



Equipment (source, DAC) makes very little difference. Note: this is JUST error rates, it has NOTHING to do with how things sound, that is a completely different test.



With longer cables, giving lots of errors, DACs vary a lot in how they handle errors.



John S.
 
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