The Mexico City "Aida" is not for audiophiles or the fainthearted: it is one of those awful crackly pirate recordings that pick up the prompter as well as the singers.

But in the 1990s, the number was reduced to 20%, with retail value of pirate recordings in 1995, estimated at US$15 million.

Among Sébastian's "pirate" recordings are Elektra (1966) and Salome (1967), both with Anja Silja.

After listening to a pirate recording of that concert, Will Crutchfield wrote in The New York Times: "What a sound!

Eavesdropping on recording sessions, particularly the parts never intended for release, is one of the great guilty pleasures of record collecting, and one that is usually satisfied by pirate recordings rather than commercial releases.

After the 1997 recital, I searched in vain for a pirate recording of it.

The pirate recording of the Berlin Lucia has been a huge success on LP and even now on CD.

Mr. Clark figures that he listened to nearly 100 Bernstein performances - tapes of old radio broadcasts, mostly, plus the occasional pirate recording - in deciding which pieces to recommend for the compact disc set.

Also still on hand are shelves devoted to the shop's specialty: rare vocal records, including the pirate recordings of live performances.