The first discussing RFIhttp://brneurosci.org/interference.html
The second discussing Common Mode noise.http://www.maxim-ic.com/app-notes/index.mvp/id/2045
Of particular note see "cables and noise" in the second links.
So cables and power cords under all circumstances can never make a difference? I don't think you all should be so quick to say "never." My house has a clear improvement with a conditioner that addresses both common mode and RFI issues. (Furman It-Ref 20i, and Surgex RT-1120.) If I run my my Lexicon MC12 and LX7 amp unbalanced the noise floor is awful. Run it balanced and there is a dramatic improvement in noise floor. Likely due to Common Mode noise removal.
An example of what noise can do: Have an JVC RS20 projector connected to a PurePower 1050 power regenerator/ups. The unit has a couple of MOVs in it but it does not have a very robust surge protection stage. As a reult I put a BrickWall unit prior to the UPS, with an Aluminata cord on the RS20 projector. The picture was remarkable. Decided to upgrade the BrickWall to a Furman so I could turn on the rear sub with a switch. Also added a dedicated 20 amp line with JPS ac wire. What was the result? A disaster. A much noisier image resulted with a big hit on the sharp 3d like improvement I got with the brickwall/Aluminata addition. I was dumbfounded since I even cleared the Furman with both Purepower and Furman. After extensive reading I finally found the problem. The UPS MOVs and preceeding Furman's MOV (hybrid multi-stage protection Series Mode and MOV), combine to cause extensive noise to the ground.
An excerpt from Surgex
2/ "Surge protectors which have MOVs only between live and neutral divert energy only to neutral and do not contaminate the ground wire, but they are also not effective at completely protecting equipment. Not having any MOVs or other shunt devices to ground, they allow live and neutral to float with respect to chassis ground up to dangerously high voltage levels during a surge event. To use the technical term: they convert normal-mode surges to common-mode surges. Common-mode surges are normally only found at low, harmless levels on branch circuits, but when generated by such a piece of equipment they can be large and damaging. Power supplies in electronic equipment may be damaged, and equipment that has a common-mode filter on the AC power input will almost certainly be damaged. Common-mode filters often have capacitors from live and neutral to ground and these capacitors will be blown out by the large common-mode surges that are generated by this type of surge protector. It is extremely important that no other surge protectors which have MOVs to ground be plugged into the type of surge protector which has MOVs only between live and neutral. To do so will convert the protection back to the type which has MOVs between live, neutral and ground resulting in ground contamination exactly as per the discussion in (1) above. There is also the risk of blowing out the MOVs that are inside the second surge protector. This also applies to UPSs since most UPSs have MOVs between live, neutral and ground. Whereas it has been standard practice for many years to plug a UPS into a SurgeX in order to protect the UPS front-end, plugging a UPS into a surge protector which has MOVs only between live and neutral cannot be recommended for these same reasons. The SurgeX True Series Mode architecture effectively “disconnects” MOVs inside any equipment plugged into it but this is not the case with other architectures"
Furman and SurgeX now both confirm the problem and recommend removal of the Furman and replacement with a dedicated Series Mode device or nothing at all. The result of adding the JPS ac wire, the dedicated 20 amp circuit, and the SurgeX 1120-RT was amazing and now curiously improved the picture further than the BrickWall/1050 combo . The SurgeX in addition to common mode noise (like the brick wall) has additional differential/normal mode removal. How is this relevant when the UPS recreates perfect power/sine wave is beyond me.
Noise has a direct effect on video and audio signals alike. That is why interconnects,power cords and proper power conditioners can, under the right circumstances, systems, and environments make an appreciable improvement. YMMV.