“Timbral beauty is an important aspect of a singer’s voice, but certainly also elusive: what is beauty and from what does it emerge? Yet, the beauty of a voice is often striking, but perhaps, and even more so, the ugliness of some voices.”
Here’s a human example from the paper [ .wav format ]
And a synthesised example [ .wav format ]
See ‘The KTH Synthesis of Singing’ by Johan Sundberg
[Research research by Martin Gardiner]