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In Reply to: RE: DIY USB Cable posted by Duster on October 4, 2017 at 17:07:46:
Preface this with the thought that we're likely dealing with very small differences in the sonic signature between competing USB cables that meet the USB "Implementers Forum" published spec. But there my be very small differences in the physical construction of the cable that enter into the equation.
Excuse me if I have this wrong, my UHF experience goes back to vacuum tubes. However it scans that:
1. Any "bits is bits" argument is out the window for isochronous audio travelling (half duplex) on USB cable... Aspects of high frequency transmission lines enter into it biggly.
2.The twisted pair of data wires in a USB cable need to be exactly equal in length, and about perfectly evenly, symmetrically twisted. Anything other may cause phase shift => timing inconsistencies => jitter. Reasonable tests suggest you can really hear jitter.
I looked up the USB spec and, if I understand it, the maximum skew introduced by the cable between the differential signaling pair (D+ and D-) must be less than 100 picoseconds. Wow.
While it's not exact to speak of the "frequency" of digital signals, such small of a phase shift at such a short characteristic "wavelength" might result from perhaps nanometers differing lengths between D+ and D- wire lengths?? Or am I all wet?
Upshot would suggest that you want darn-near perfect, machine-made twisted pairs for USB. Twisted to minimize noise pickup. Perfectly matched in length to minimize jitter.
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Follow Ups
- About USB... - mr.bear 11/2/1713:01:32 11/2/17 (5)
- RE: About USB... - beautox 01:49:23 11/3/17 (3)
- RE: About USB... - Ryelands 05:51:27 11/3/17 (2)
- RE: About USB... - beautox 07:36:44 11/3/17 (1)
- RE: About USB... - Ryelands 07:52:40 11/4/17 (0)
- RE: About USB... - Duster 14:08:12 11/2/17 (0)