Why do AC cords make so much difference?

I believe Sean is fundamentally correct in significant parts of what he is saying. Good recording studios routinely use large transformers, shielded low inductance in-wall wiring, dedicated circuits, and extremely low noise grounding systems for house current. It's not cheap to do, but it makes more sense than buying equally expensive audiophile line conditioners that are basically inadequate to do the a/c cleanup.

On cables, the jury might still be out. Perhaps it's just tone controls interacting with poor component design, but it would be nice to have a consistent understanding of why sound changes so much with cable design.

Back to the "floating ground" issue. I was told by a supposed cable guru that one shouldn't "float" the ground on digital gear, because digital gear uses the ground to shunt the digital garbage, "grunge", "error bits", or whatever you want to call it, away from your system. Therefore, I was told, using the "cheater" plug to defeat the ground eliminates the route of escape for this unwanted byproduct of the digital gear allowing it to enter the other components in the system.

Any thoughts out there from the experts?

Baloney - there is no requirement for an earth ground. There is no "shunting" of noise necessary unless the power supply is letting power line HF noise through - this is unlikely. My transport has no earth ground and it is superb.

Digital is NOT an audio signal at it's point of origin or when being transferred in digital form. It is an RF based signal that operates above 3 MHz. As such, a design that makes use of some type of bandpass, high pass or low pass filtering or has bypass caps in the design may require a low resistance Earth ground for optimum operation. The reason that a designer would shunt such signals to ground would be to try to keep stray signals from "leaking out" or interfering with other sections of the player. While the device would still "work" without having a low resistance path to ground, it might not be performing up to snuff or meet spectral purity as documented by the FCC in terms of spurious emmissions / interference. As such, not all designs are the same when it comes to grounding, nor should they be treated as such. Sean
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Great post, Sean. Thanks.