07-28-12: Richard_stacy
The latest find for me is the USB cable that connects my exterior drive to my server. If you read the forums or ask and "expert" they will tell you this cable will not impact sound. Most will say the USB cable that connects the server to DAC will but even some guys say that will not. Well...in my system they both do and not in subtle ways. Changing the feed from my HDD to server from generic eSATA cable to an Acoustic Revive USB cable has been a transforming event for my systems performance.
From a technical standpoint, I for one don't find that to be at all surprising, Richard.
Since you are apparently connecting the server to the DAC via USB, presumably the DAC and the external HDD are located not all that far apart, probably in the same room. Therefore RFI emissions from the HDD cable could couple through the air to the DAC and/or its cable, affecting jitter. Digital noise associated with the signals that are present on the HDD cable could also couple into the DAC cable through the common ground connection they have with the computer.
Those kinds of effects could very conceivably, IMO, have sonic consequences that would vary among different cables of the same type (e.g., USB). But changing from eSATA to USB introduces additional variables that are likely even more significant. In doing that, you've made major changes in the technical parameters of the signals being conducted by the cable, including risetimes and falltimes, which directly relate to RFI and noise. You've also changed the interface circuitry that is being used in the HDD and the computer, and you've changed the involvement of the CPU and related circuitry in the computer in processing the transfer of data. All of that likely affects the timing, magnitude, and frequency components of computer-generated noise, some small fraction of which probably ends up being conducted into the DAC, affecting jitter and/or bypassing D/A conversion and directly affecting analog circuitry in the DAC.
Of course, as we've discussed in other threads, IMO these kinds of effects figure to be highly system-dependent, and to not have a great deal of predictability, and to have a degree of correlation between cable performance and cable price that is much less than perfect.
Best regards,
-- Al