Beatles Unknown "A Hard Day's Night" Chord Mystery Solved Using Fourier Transform
scientificblogging.com
scientificblogging.com
George Harrison on 12-string pairs 2 through 5: (A2 A3) (D3 D4) (G3 G4) (C4 C4)
George Martin on piano: D3 F3 D5 G5 E6
John Lennon on 6-string: C5
Paul McCartney on his Höfner bass: D3
Expert mixing masks the timbre of the piano amongst the guitars, leading to the "mystery."
It's a cute demonstration of basic physics, more-or-less at the freshman level (although lots of high school students could follow it). It doesn't claim to be anything else.
UPDATE: Finally got the blog link to load. While the original paper is modest in its claims, the blog hypes them up and then fails to cite the original paper. This blogger does not earn a cookie.
Once the author has a list of pitches though, the process of assigning pitches to instruments is very well laid-out. The key to locating the piano was that piano strings are hit in triplets, and each string in a triplet is tuned ever so slightly differently.
Signal processing was one of my favorite courses in college.
The fact that it's not reproducible on a standard-tuned guitar might have stopped guitar players from figuring it out on the fretboard though.
According to the article, this specific chord has been debated for decades by people with good ears.
I feel less dumb today knowing clearly exactly how that would work. Although I would have thought it would in practice be feeding it into an audio analysis app and picking the peaks and mapping them to notes on various tunings. Not really mathematics though, but cool none the less.