More than any great singer of the 1950s, Maria Callas’s legacy deserves to be considered from two different perspectives. Her studio career from 1950 to 1965 is one thing, and rightly a cause for celebration. However, there are many who will tell you that her defining work was done on the stage, where her gifts as a vocal actress were allowed full play in tandem with her ahead-of-their-time dramatic abilities.

But here’s the rub: no great singer of the 1950s has been so poorly served in terms of live recordings. Devotees have had to struggle for decades to get a handle on the voice, straining their ears through layers of static, distorting microphones and a sense that the action was going on somewhere else in the building, in fact anywhere but where the listener happens to be right now.

Three years ago, Callas fans were rightly thrilled at the efforts of Warner Classics engineers who went back to the original tapes to remaster the studio recordings. The results were transformative with greater clarity, resonance and a natural sonic stage permitting La Divina to shine more brightly than ever before. Even more excitement, therefore, greeted the news that Warners would be revisiting...