Hi,
I have some questions regarding USB cables and measurements.
Currently I'm using a cheap printer USB cable and always have the doubt if a replace makes sense.
QED Cable
Trying to look for measurements in USB cables published by the manufacturers found this cable:
https://www.qed.co.uk/reference-high-resolution-usb.html#tab1
Which has some measurements of the cable performance, not of the output signal of a DAC, but at least is something:
- Characteristic Impedance: 90 Ω +/-5%
- Signal Pair Attenuation: < -0.11 dB/m @ 480 MHz
- Propagation Delay: 26 ns max
- Propagation Delay Skew: 68 ps max
- Maximum Data Rate: 480 Mb/s
- Worst case time related jitter: < 76 ps pk-pk (5 m cable measured at 480 Mb/s; 440 mV rms)
They also have a section with "papers".
https://www.qed.co.uk/cablesmatter
Allo Cable
I saw that they mention the controlled impedance feature and later on found that Allo also sells a USB cable mentioning the same:
https://www.allo.com/sparky-eu/flex-cable.html#features
Questions
Are any of the QED's measurements relevant to the final audio output? Or just electrical characteristics of the cable that exist but doesn't make any difference? If the DAC has its own power supply, does the jitter measurements of USB cables matter at all?
Since Allo seems to be an honest company from the "science" point of view, how do you interpret this? Theoretically, can there be really any audible difference in some system when using a cable with a more accurate impedance? I say theoretically because to some extend I understand that cable manufacturers try to build a good cable based on measurements of the cable itself, and not plugged into a system, simply because they can't assume that there isn't a system out there affected by the quality of the cable. I mean, from their perspective, the fact that no one it's been able so far to pass a blind test of two USB cables doesn't rule out that it could happen some day.
Thanks!!