Robust and athletic, Baum was at one time the amateur heavyweight boxing champion of Czechoslovakia and member of Max Schmeling's Sports Club in Cologne.
Baum's roaring spinto voice easily reach the high-D flat in the Rosenkavalier Italian singer aria, in which he had express permission (via a letter) from the composer to interpolate the note.
His repertoire included cornerstone spinto roles such as Don Alvaro, Radames, Cavaradossi, Manrico, Lohengrin, Walther von Stolzing, Don José, Canio, Samson, Des Grieux, Turiddu, Enzo, Pollione, and Andrea Chénier, which he played beside such illustrious colleagues such as Maria Callas, Renata Tebaldi, Zinka Milanov, Eleanor Steber and Risë Stevens.
Recordings include the Lohengrin Bridal scene with Helen Traubel from 1945 which finds him in an ardent, heroic mood, underpinned by his characteristically strident technique.
[1] Several of his live performances as Pollione, Radames and Manrico beside Maria Callas in their 1950 Mexico tour were especially noted for the high degree of excitement generated, though he never sang at anything less than full volume.