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Do USB Audio Cables Make A Difference?
- Thread starter amirm
- Start date
This is the one I'm using:
https://www.ebay.co.uk/itm/6N-oxyge...A-TO-B-/273158431279?var=&hash=item3f9982e22f
I bought it because I liked the colour and because of well described feature set:
Features: Using a 0.2mm oxygen free copper and silver stocks +6 11 0.08mm 99.9999% of ultra high purity oxygen-free copper wire is made, the low high school three-band mix just right.
"The low high school three-band mix just right" feature seemed especially attractive to me!
https://www.ebay.co.uk/itm/6N-oxyge...A-TO-B-/273158431279?var=&hash=item3f9982e22f
I bought it because I liked the colour and because of well described feature set:
Features: Using a 0.2mm oxygen free copper and silver stocks +6 11 0.08mm 99.9999% of ultra high purity oxygen-free copper wire is made, the low high school three-band mix just right.
Rough diameter 7mm, easy to carry the line is soft.
Plug are gold-plated copper ferrule, metal, strong anti-interference, effective antioxidant, connection is stable, reduce the signal attenuation, to ensure good qualitytransmission effect
"The low high school three-band mix just right" feature seemed especially attractive to me!
graz_lag
Major Contributor
IMHO, there should be two types of USB cables available * in the market as exclusively designed for audio D/A applications :
* I know very little abt. the catalogs issued by the USB manufacturers for audio applications ...
one type that includes both digital signal transfer and DC
another type that includes only the digital signal, to be used on DACs with their power supply in
If - in these DACs, the 5V lines are terminated, the use of USB cables that carry also the DC, it would cause a ground loop, so noise, unless they are transformer isolated.
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graz_lag
Major Contributor
I'm late on this thread ... do you hear the whistling from my brakes ?
Here's one who prefers 75 Ohms - and better 110 Ohms, over the USB for his audio digital transfer, from a pure sonic results.
What abt. just record the digital output from a DAC that is fed via a USB cable, to see if the source file and sent file are identical ?
My point is that the most common use for USB is for moving files around, where the receiving end has some intelligence and compares its copy with the original to see if it is correct - and if not, the information is re-sent.
This is normally carried out by checksums or other similar means, right ?
Does a modern DAC, among the ones you are testing here, have that some sort of intelligence to compare it's received data to the original ?
I'm not an expert, I wonder what the impact - on the final sound, would be if there is any difference
in the data file sent vs. the one received ...
The ground connection is required for device detection.
graz_lag
Major Contributor
So, the USB port in the DAC is isolated so that the ground loop is avoided, correct ?
OP
- Thread Starter
- #67
You can't. Analog capture of a digital stream will have noise, variation in speed, etc. And will differ from run to run so no exact match can be found.
graz_lag
Major Contributor
Thank you, it's clear.
So at the end we go back to the infamous jitter as "in the real life" indication of speed accuracy between the PC transmitter and DAC receiver, right ?
OP
- Thread Starter
- #69
No, digital jitter is too small to cause audible speed variations. What I mentioned is drift. Our hearing is not sensitive to that so the clocks used in audio are allowed to change over time, temperature, etc. This is why your digital watch can lose time after a while. This drift occurs in a matter of seconds and will make run to run comparisons difficult.
Oh, so your hearing aid device can help you hear that difference too? Impressive..
Does a modern DAC, among the ones you are testing here, have that some sort of intelligence to compare it's received data to the original ?
I'm not an expert, I wonder what the impact - on the final sound, would be if there is any difference
As an expert I would say this is entirely possible --- you don't even need to test the data received against the data sent, as each USB data packet includes a checksum for that packet, and you can program the interface chip (such as xmos's xu208 in many DACs measured in this forum) in your DAC and log (print onto screen, for instance) whenever there's a checksum mismatch. But normally USB audio spec does not requires retransmit of data in case a checksum error occurred.
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Bad USB DAC or cable design could lead to audible artifacts.
This usually is lead by two issues
- some usb dac output is powered by USB power. If the power quality is very bad and the DAC power filter is not working properly , the output will be noisy.
- some bad USB cable cannot transport reliable digital signal (which means the digital signal may have very high error rate because of the power loss through the wire).
Usually these two factors are super easy to avoid --- as @amirm said, a cheap but properly implemented DAC and a normal USB cable can avoid those problems easily.
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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.
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Cable impedance is not necessarily related to length as is resistance.
Indeed so. S-PDIF and AES-EBU (both balanced and unbalanced) are incredibly rugged and pretty much anything will transmit the stream adequately for the receiver to lock, over normal domestic distances. In Studio complexes where the cable runs can be hundreds of metres, then impedance does matter, but not at short distances.
Some of us remember Canford Audio's demonstrations of AES-EBU going through two pieces of wet string. It was wet because it went through a fish tank with fish swimming about! I would be surprised if the impedance of that circuit was closely controlled....wouldn't it depend on where the fish were?
S.
AnalogSteph
Major Contributor
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.)
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