Defective voices enjoy a special immunity. The public, accustomed to their uneven or veiled tones, only perceives with difficulty any problems they may be experiencing.

[But] it is not the same with voices that are naturally pure; the more perfect the voice, the more easily the ear captures any distortion.

Faure, Jean-Batiste, et al. La voix et le chant: traité pratique. 1886.