But it’s “The Beatles in Mono” box set that’s sparked the excitement of fans. The limited edition release has already sold out its pre-order copies at Amazon.com and other retailers, according to BeatleNews.com. “The new generation of CD buyers will probably be mystified by this mono and stereo thing,” Howlett said. “But the Beatles were recording at a time when there was this transition from mono, so they really only got to grips with stereo at the very end of their career.”

The mono box also contains its equivalent of “Past Masters,” which is a double CD called “Mono Masters” that collects up mono mixes of stray single and EP tracks. These are the mixes fans originally heard on their old records, which differ from the stereo versions. For example, Heatley said, “In the mono ‘Revolution’ there’s more distortion and it’s a harder kind of ‘Revolution.’”