Two of the best singers of their generation are heard here, both of them in their prime. Caballe's voice was at its most beautiful just around this time (the recordings were made in 1969), and Verrett too had a distinctive beauty of tone, firm without hardness, extensive in range yet happily committed to the mezzo-soprano repertoire for which it was best suited. The role of Amneris came only just within that category for she never had quite the annihilating force for the attack on Aida (''Trema! In cor ti lessi!''), nor the opulent chest notes for the vindictive phrases low in the voice; even so, she was able to some extent to compensate by the concentration of tone and meaning, as she does here. In fact, the drama of these duets is remarkably vivid, and in the long scene from Anna Bolena movingly realized. Caballe has some extraordinarily touching passages, such as her forgiveness of Jane Seymour (''Va, infelice''), and in the Aida duet she goes right to the heart in ''io vivo solo per questo amor''.
The two singers match their voices well when singing together, making a particularly lovely effect in the reflectively sung cadenza of ''Mira, o Norma'' (sung in E, a semitone up from the usual and one down from the written). The exception to the general pleasure of the record is the Semiramide duet, where Caballe 'separates' the notes in scale-passages and where there is a relative unresponsiveness to mood. But it is a fine recital, well recorded and sympathetically accompanied, with a distinguished partnership forged at just the right time.'