Adding a detuned copy of a voice makes it sound like a choir.

Evidence

No one mistakes a chorus for a soloist, and vice versa. Nor are 20 violins ever mistaken for a single violin. Yet if all singers are somehow in exact lockstep unison, with no vibrato or frequency drift, the sound some distance away would be indistinguishable from that attainable by a single voice. — Eric J. Heller, Why You Hear What You Hear- An…, 418 (#complicates, via linked claim)

Categorization

• XREF: connects to: Slight mistuning among voices fuses into a single pleasant tone; A convincing chorus emerges from 5 to 10 slightly pitch-shifted copies; Perfectly synchronized voices are acoustically indistinguishable from one voice — Eric J. Heller, Why You Hear What You Hear- An…, 418

Broader Connections

• A convincing chorus emerges from 5 to 10 slightly pitch-shifted copies #corroborates (0.90)
• Perfectly synchronized voices are acoustically indistinguishable from one voice #complicates (0.80) — Eric J. Heller, Why You Hear What You Hear- An…, 418