“Ms. Caballé’s exalted status was won by virtue of the vast number of roles at her command; the length of her performing life; and the lather of adoration into which her fans routinely whipped themselves. … But above all — and this is what moved her fans to ardor in the first place — there was the voice itself. For sheer vocal glory, reviewers wrote, few voices, if any, could rival Ms. Caballé’s.”