@millercarbon - right, but if you want to get your hum levels down to below 70 -75 dB, you will need to do more than just set wires a few inches apart. Your comment is not informed, it is just biased, and incomplete.
@rodman99999 - Apparently, the original posting link and paper was deleted for some reason. Unfortunately, MS Edge didn't think the link was important, so it dumped it along with a number of other informative links.
Regarding the spacing and 90 degree crossing, all I can say is, when I put a voltmeter on my system and fought to get hum and hum related noise below -70 dB, it took an entire 3 day weekend. I found that I needed dual ferrites on the less expensive wall warts that were several feet away from the phone inputs and my big Marantz Class D amp had to be two horizontal feet away from the Stax Headphone amplifier. I discovered any low level hum at all dissolves clarity and definition, even at louder volumes, so the long effort was well worth it.