High-pitched soprano singing is unintelligible because harmonics are too sparse for formants

Evidence

Another commonly known phenomenon is that trained soprano singers may produce such high pitches that the harmonics are sparse in frequency, so that the formant structure is not present in the signal. This makes high-pitched vocals unintelligible. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 631

Categorization

• XREF: Connects to the intelligibility tradeoffs in speech synthesis and communication design that this reader explores across the book.
• corroborated: 2 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 631