I wouldn't agree with Eric Clapton about much, but he's always been bang on the money when it comes to Robert Johnson. Clapton once described Johnson as, "the most important blues singer that ever lived". The recordings that Johnson made between 1936 and 1937, collected in two volumes entitled King of the Delta Blues Singers, not only mark the apogee of the blues form, they stand among the most influential recordings of all time. Johnson's songs come at the listener with such combustible force that they sound for all the world like the very first rock'n'roll recordings. In the years following his death in 1938, Johnson's story was reshaped as myth, largely thanks to the wonderfully daft notion that he'd sold his soul to the devil in order to master his guitar and play the blues. The myth endures but the extraordinary power of his work has ensured that the music effortlessly transcends the myth.

And now, nearly 50 years after Columbia first packaged his work as King of the Delta Blues, we discover that we've been listening to these immortal songs at the wrong speed all along. Either the recordings were accidentally speeded up when first committed to 78, or else they were deliberately speeded up to make them sound more exciting. Whatever, the common consensus among musicologists is that we've been listening to Johnson at least 20% too fast. Numerous bloggers have helpfully slowed down Johnson's best-known work and provided samples so that, for the first time, we can hear Johnson as he intended to be heard.

As we speak, I'm listening to a slowed-down version of Come on in My Kitchen. The original version is so familiar to me it's practically cemented in my DNA. Once accustomed to this slower version, acclimatised to the lower-pitched vocal and less hectic guitar, I find it even more beautifully haunting than the rendition I've known and loved for more than 30 years. In the new version Johnson sounds more natural, exactly like he ought to sound.

Initially though, the effect is not a little disconcerting. Not unlike the childhood experience of deliberately playing records at the wrong speed for a laugh, invariably bringing on bouts of dizziness and nausea. After a certain age (say, seven) the novelty of playing songs at the wrong tempo tends to wear thin, although it was always highly entertaining to hear John Peel regularly get his 33 and his 45 RPM mixed up. On one memorable occasion, Peel distinguished himself by playing an entire side of Fripp and Eno's No Pussyfooting backwards. Brian Eno was the only listener to notice anything was amiss.

If hearing music at the wrong speed is the sort of thing that grills your kippers, then you might want to check out the supremely bonkers back catalogue of Brighton-based Wrong Music. For the rest of us, the right speed will do just fine. Like me, you might be left not a little incredulous to learn that some of the most beloved albums in the canon were released at the wrong speed. As late as 2003, a music professor pointed out that all the early Doors albums, on vinyl and CD, had been slowed down due to a cock-up at the mastering stage. When Kind of Blue was first released on CD it received ecstatic reviews despite the fact that Miles Davis' trumpet was at the wrong speed on half the tracks. There are those who swear blind that the vinyl version of Dylan's Sad-Eyed Lady of the Lowlands from Blonde on Blonde was mastered at the wrong speed as it plays at a quarter-tone below the CD version. Most famously, all the original Rolling Stones ABKCO releases were mastered at the wrong tempo, an error first noticed by Keith Richards when the albums came out on CD.

Does any of this matter? Well, I don't know about you, but I'd prefer to hear an album as it was meant to be heard, rather than a version birthed by a studio muppet flicking the wrong switches as he lights up another jazz woodbine.

In the case of Robert Johnson, we have much to be thankful for. After years spent listening in awe to his blues masterpieces, we can now enjoy his work as if hearing it for the first time. Just as soon as Columbia pulls its finger out and releases his 41 recordings at the right speed. It won't win Johnson his soul back, but at least we finally hear the world's greatest bluesman as he actually sounded in that lonesome San Antonio hotel room back in the mid-30s.