The descriptive note comes from item B0279 in :
Cowden, Robert H.
Concert and opera singers
A bibliography of biographical materials
Compiled by Robert H. Cowden
Westport, Connecticut: Greenwood Press, c1985, 278 p.
This is what Robert H. Cowden had to say:
The author includes twenty-three singers among the fifty artists he has asked to discuss their lives and careers. All of them were well-known in Germany at the time
© Robert H. Cowden
(c) 2022. Frank Greene. All rights reserved.