Why records are off pitch.

On tape, pitch and speed are tied together. Play a tape faster than it was recorded and every note rises; play it slower and every note falls, and the tempo moves with it.

The rule: divide the playback speed by the recording speed, take the base-2 logarithm of that ratio and multiply by 1200. In plain words, every 1 % of speed is about 17 ¢, and about 6 % is a whole semitone.

A song 1 % fast gains barely more than one beat per minute at 120 bpm, far too little to notice. A small mismatch between the machine that recorded a tape and the one that later played it back was enough for 5 or 10 ¢, about where a player starts to notice it against the record.

Studios also changed the speed deliberately, with a control usually called varispeed: to make a voice sound younger, to reach a vocal line, or to make two takes meet. A change of exactly one semitone leaves the record on the A 440 grid in a new key; a change that is not a whole number of semitones leaves it off the grid.

• The Beatles' Here Comes the Sun was sped up after it was played, and measures about 35 ¢ sharp.
• Lovely Rita was slowed in the mix and sits at about A 425, between E♭ and E.
• When I'm Sixty-Four was recorded in C and sped up by about a semitone, to D♭. It measures about 9 ¢ flat, with the rest of the album.
• Across the Universe, recorded in 1968, was slowed down for the Let It Be album and now sits about 25 ¢ above E♭ Standard.
• The Rolling Stones' Fingerprint File was mastered faster than it was played, B minor becoming C minor; it reads about 13 ¢ flat, and tabs follow it with a capo at the 1st fret.
• Led Zeppelin's No Quarter was slowed with varispeed yet measures about 4 ¢ sharp, back on the grid, which fits a change of a whole semitone.

Sometimes only part of a song moves: the end of Black Sabbath's War Pigs was sped up, so its last minute climbs above the pitch of the main riff.

Small electronic tuners only became cheap and common from the late 1970s. Before that a band tuned to a piano, an organ, a pitch pipe or a tuning fork, or simply to one guitar, and everyone landed wherever that reference was. A studio piano tuned a little high pulls the whole take up with it, and a Hammond organ's pitch is fixed by its motor, so the guitars tune to the organ.

• Kyuss had no tuner, by bassist Scott Reeder's account, until he joined in 1992. Wretch sits mostly about 40 ¢ under C Standard, with some songs lower still; Welcome to Sky Valley, Reeder's first album, sits steady about 8 ¢ sharp.
• Van Halen. Eddie Van Halen tuned by ear and Michael Anthony tuned his bass to him. The debut sits about 13 ¢ above E♭ Standard, Van Halen II about 28 ¢.
• AC/DC. The Bon Scott albums sit 10 to 34 ¢ flat as a whole, with single songs from 63 ¢ flat to 44 ¢ sharp. From Back in Black (1980) on, every measured album sits within about 12 ¢ of A 440, most of them right on it. Tape, tuning or both: the cause is unknown, the change is plain.

A tuning, a machine's speed and a piano's pitch hold for a session, not forever. Songs recorded on another day can land somewhere else, even on the same album.

• The Beatles cut ten songs of Please Please Me on 11 February 1963. The album sits about 28 ¢ flat, but the two songs from the morning session, There's a Place and I Saw Her Standing There, are only 12 and 9 ¢ flat.
• Black Sabbath recorded Evil Woman a week before the rest of their first album, in another studio. It sits 13 ¢ above the songs from the main day.
• On Nirvana's Nevermind, the songs from the May 1991 sessions run about 14 ¢ sharp, while Polly, kept from a 1990 session, sits at A 440.
• AC/DC's Rock 'n' Roll Damnation, recorded last as a single, sits 16 ¢ under the rest of Powerage.

A CD transfer, a remaster or a new LP means playing the master again, and the speed does not always match. TuneLit measures several editions where the owner has them:

• Early CDs. AC/DC's American CDs of High Voltage and Dirty Deeds Done Dirt Cheap run about 6 ¢ faster than the Australian CDs and the remasters. The 1993 MCA CD of Jimi Hendrix's Are You Experienced runs about 21 ¢, or 1.2 %, slower than the three other editions.
• Remasters. Iron Maiden's 1998 remaster of Powerslave reads about 15 ¢ higher than the 1995 CD and the 2015 remaster. Nirvana's 2009 Bleach runs about 16 ¢ higher than the 1992 CDs.
• Remixes. Megadeth's 2004 remix of Youthanasia moves several songs 12 to 50 ¢ higher, while the remix of Peace Sells stays as flat as the original.
• Vinyl. Radiohead's In Rainbows LP reads about 14 ¢ sharp, but its songs run 0.8 % shorter than on the CD. 0.8 % faster is exactly 14 ¢: the LP copy played that much fast, on the turntable or in the cut, so the CD most likely sits at A 440. It can go the other way. Both LPs of The Beatles' Revolver that TuneLit checked play 8 to 10 ¢ lower than the 1987 CD, and so does the song Yellow Submarine on another CD: so the 1987 CD is probably the fast one here.

The pitch you need is the pitch of the copy you play, and two copies of one album can differ by anything from a few cents to more than 20 ¢.

• Every measured album page names the copy TuneLit used, such as a 1986 Atlantic CD, and its notes say how other editions compare. If yours is that one, press Tune and play.
• With another edition or a stream, start from the Tune setting and hold a chord against the record. If it beats, nudge the reference a few cents until the wobble slows down.
• If you have the file, load it in Play along: it measures your own copy and can shift the song to your tuning instead.