They did 24 bit remastering from the original tapes-- and did a shitload of cleanup -- scrubbing all sorts of imperfections in the source tape. #1 example is She Loves You.
She Loves You exists ONLY in the form of the original mono master made in 1963. The original 2 track recording is missing.
The original 1963 tape, having been pulled off the shelf perhaps dozens or hundreds of times and put through the wringer, so to speak, was in horrible shape in 1986 when they did the original master.
The original recording is edited in several places, and on CD the splices/drop-ins and tape drop-outs/imprefections shine through. Listen to the original (Past Masters 1), if you can take the treble, LOUD through headphones. Then listen to the version on 1.
Version on 1 is MUCH clearer, less harsh, and they have edited out 3-4 icky transitions/tape defects.
Some other noticeable examples:
Hey Jude - the orchestra sounds much warmer and fully present
Paperback Writer/Rain- much better bass response, as is the bass response throughout.
As alluded befoer- even though the Help/Rubber Sould songs were re-edited digitally for the '86 CDs, Ticket To Ride REALLY blows the speakers out in the One version - much much better bass.
Even Love Me Do warbles MUCH MUCH less than the one on Past Masters.
Just think what they could do with the entire catalog (!)
Everyone's talkin' 'bout the President
We all chip in for a bag of cement