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Do USB Audio Cables Make A Difference?

Krunok

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#81
It would depend on the frequencies involved, don't you think? A 1 m cable qualifies as a lumped component only up to about 30 MHz. USB 1.1 @11 Mbps isn't likely to care, USB 2.0 high-speed @ 480 Mbps might, and USB 3.0 definitely will. (Found a lil' article on the challenges of high-speed USB 2.0 on board layout from back in the day.)

That said, 90 ohms vs. 75 or 110 isn't a huge amount of mismatch (that's like -20 dB of s11 tops), so I wouldn't expect any really bad reflections. The 100 ohm twisted pair that goes in ethernet cabling would be an even closer match. I do have to wonder why they went with 90 ohms for USB, that's quite low for TP.

In fact, characteristic impedance is entirely independent of length by definition. Resistance, of course, will depend upon length and conductor diameter as you would expect, and a manufacturer could cheap out in ways that would push certain devices over the edge. (Some bus-powered interfaces were notorious for doing it even with good cables, like a certain Terratec that would develop a habit for crashing regularly... was it the 6fire USB? In this case proper operation would be restored by shorting out a choke in series with supply voltage, bypassing its resistance.)
Nothing spectacular would happen with USB 3.0 if you use 3m or 5m cable with so small impedance mismatch - you may only not be able to achieve top speed, but I doubt it. With audio this wouldn't present a problem, even with HiRes.

And I repeat once again, I believe 75 ohm and 110 ohm impedance were mentioned in the context of coax SPDIF, not USB.

I'm not sure what people expect to hear once impedance really starts to become a problem but the only sound they would hear in that situation would be the sound of silence. ;)
 

DonH56

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#82
Improper impedance matching of even short cables can impact high-speed links. I had to debug a board that had a mismatch causing a glitch in a 100 MHz clock signal that was causing failure. Wideband data streams as found in high-speed USB are not audio signals. I do agree a small'ish mismatch may not cause problems most of the time.

The impedance of a cable is somewhat weakly dependent upon resistance. High resistance (which is NOT the same as impedance) will increase loss, of course.

Impedance Z = sqrt[(R + jwL) / (G + jwC) where R = resistance (usually small), L = inductance, G = conductance (usually small), and C = capacitance

For a lossless line, Z = sqrt(L/C)

There are Wikipedia articles on component impedance and transmission-line impedance (probably under "characteristic impedance" -- I was too lazy to look).

HTH - Don
 

Krunok

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#83
Improper impedance matching of even short cables can impact high-speed links. I had to debug a board that had a mismatch causing a glitch in a 100 MHz clock signal that was causing failure.
Sure it can, on high frequencies such as 100MHz. But have you ever heard anybody had problems with cable impedance with USB and SPDIF cables?

C'mon guys, let's be realistic in this discussion.. ;)
 

SIY

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#84
maybe his dac or computer is not rigorously implemented so that such impedance change can cause signal defect. In my view that’s entirely possible.

Usually usb cable should have ~ 90 ohm impedance. 110 or 75 is not a small deviation away from the spec and could change the signal in some very audible way.
"Audible" in the sense of pops and dropouts. The often-claimed changes in the quality of the sound... no.
 

DonH56

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#85
Sure it can, on high frequencies such as 100MHz. But have you ever heard anybody had problems with cable impedance with USB and SPDIF cables?

C'mon guys, let's be realistic in this discussion.. ;)

Many times. USB 2 data rate is 60 Mb/s, USB 3 is 625 Mb/s. USB 3.2 is 2.5 Gb/s. That seems pretty high though well below what I deal with in my day job... BUt I have had to deal with poor USB links many times over the years.

The AES-S/PDIF issue may be partly due to misunderstanding the spec. Balanced AES specifies 110-ohm cables; unbalanced AES and S/PDIF specify 75 ohms. They run in the MHz range and allow cables from 10 m to 1000 m so yes I have seen problems there as well. Guess our experience just differs.

The problems I have seen generally occur at the connectors and boards rather than the cables themselves if That's what you are arguing. Most vendors buy the same or similar cables (not that many raw cable manufacturers) and they meet spec.
 

Krunok

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#86
"Audible" in the sense of pops and dropouts. The often-claimed changes in the quality of the sound... no.
I would put my money on the bet that no sound would come at all if you exceed max cable length or impedance becomes a problem (which is extremely unlikely in home use).
 

Krunok

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#87
Many times. USB 2 data rate is 60 Mb/s, USB 3 is 625 Mb/s. USB 3.2 is 2.5 Gb/s. That seems pretty high though well below what I deal with in my day job... BUt I have had to deal with poor USB links many times over the years.
Really? When transferring audio over USB or data?

The problems I have seen generally occur at the connectors and boards rather than the cables themselves if That's what you are arguing.
Well, partly.. I'm arguing that chances that everything will work fine with cheap USB cable between average notebook and not so crappy DAC are actually extremely good.
 

Krunok

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#89
USB has a fixed rate at the link level. For high-speed USB 2.0 it is 480 Mbps. Audio data is sent in bursts every 125 μs, each containing however many samples result in the correct average rate.
Now who would guess that..

Guys, this topic has become pissing contest about something that is absolutely not an issue in real world of home audio enthusiasts.
 

amirm

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#91
I would put my money on the bet that no sound would come at all if you exceed max cable length or impedance becomes a problem (which is extremely unlikely in home use).
Oh you do get sound. Recently I had a 6 foot or so USB cable I was testing with a DAC and just occasionally I would hear a subtle tick. Changed the cable and all was well. This was a cheap generic USB cable by the way.

I have also caused USB data loss using two USB extension cables strung together.

Here is one version of how it sounds: https://www.dropbox.com/s/rdbweo5mkxsocpt/Behringer Extension cable without Iso Regen.wav?dl=0

And with a less performant USB receiver:
https://www.dropbox.com/s/h36zguooded28l4/Behringer Extension cable with Iso Regen.wav?dl=0
 

graz_lag

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#92
... I have also caused USB data loss using two USB extension cables strung together ...
This experience of mine is related to USB data transmission, not audio, but I'd like to report it just as support to what you have experienced ...
In my packaging machines, there are several brushless motors, to which I communicate by means of a very standard USB 2.0 cable.
However, I am not allowed to go any longer than 6 feet nor to use any extension, otherwise the receiver into the brushless motor VFD rejects the transmission, it keeps saying "data transmission error" ... :rolleyes:
 

mansr

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#94
I think this thread is a perfect place to ask someone to explain this 8kHz noise thing.
That is caused by the 8 kHz packet rate in high-speed USB 2.0. Whenever a packet is being received, the power consumption of the receiver increases a little, and the processing of the packet also causes some additional electrical noise. In some DACs, these variations couple, one way or another, to the analogue side as noise at 8 kHz and its harmonics.
 

yue

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#96
I think this thread is a perfect place to ask someone to explain this 8kHz noise thing.
8khz noise is irrelevant to this topic. 8khz is the frequency for each packet transferred. The thing discussed here is the USB packet error caused by bad components, either bad cable or bad USB interface design.
 

graz_lag

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#97
Oh, so your hearing aid device can help you hear that difference too? Impressive..
Come on ... you know that I am not claiming any sorts of dramatic sound differences between the different configurations of mine ...

As I always say, listening to music is very much - and ultimately, a subjective experience.
I perfectly accept / acknowledge that you feel a "better" sound with that particular tonal balance with the added distortions out from your tube amplifier. As long as you like it, I am very happy for you, indeed.

When I am saying I hear differences between the USB and balanced 110 Ohms, I perfectly know that the reason is related to how the associated infeed has been implemented inside the DAC. Logically, that applies only and exclusively to my setup.
It could perfectly possible that those feelings of mine would not be confirmed on a different setup. (I am pretty sure they will not ...)

By the way, I use cables from Supra, Sweden :

USB 2.0 (http://www.jenving.com/products/view/usb-2.0-a-b-blue-1m-1001907573)
DAC-XLR DIGITAL BLUE PC (http://www.jenving.com/products/view/dac-xlr-digital-blue-pc-1m-1001900107)

I buy these Supra's vs. the cheapest ones for reliability, not audio quality. And because - as many of us here in this forum, I love numbers, Supra is one of the few manufacturers who publishes the electrical performance, so - at least, you know what you get for your money ...
 

bennetng

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#98
That is caused by the 8 kHz packet rate in high-speed USB 2.0. Whenever a packet is being received, the power consumption of the receiver increases a little, and the processing of the packet also causes some additional electrical noise. In some DACs, these variations couple, one way or another, to the analogue side as noise at 8 kHz and its harmonics.
Thanks. Very useful info.
 

DonH56

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#99
Really? When transferring audio over USB or data?
Yup. Data is data and dropped bits are dropped bits; there is no analog audio path through USB.

Well, partly.. I'm arguing that chances that everything will work fine with cheap USB cable between average notebook and not so crappy DAC are actually extremely good.
As I said, our experience differs. "Extremely good" was not your original premise. But, this seems like another religious debate wherein neither of us is likely to change the mind of the other.

Have a good day - Don
 

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