Put all five together and you have a warm, seamless and irresistible wall of amplified vocal sound, supported by near-perfect breath control, tuning and rapport.

Earlier ornithologists puzzled for centuries over how the sound was made, with many believing that it was a vocal sound.

The words were hard to hear, while the awe at massed vocal sound and spatial effects wore thin too early in this repetitive 45-minute epic.

There are four physical processes involved in producing vocal sound: respiration, phonation, resonation, and articulation.

Other characteristics are a call and response between the soloist and the chorus, and an especially tense vocal sound.