Stretched and Compressed Scales
You will hear a melody played in a high register with an accompaniment in a low register. Which of the three presentations sounds most in tune?
This demonstration illustrates that to many listeners an overstretched intonation, such as case #2, is acceptable, whereas a compressed intonation (#1) is not. About 40% of a large audience will judge #2 best.
Intonation compressed (Bass: C ; Melody: B)
Intonation stretched (Bass: C ; Melody: C#)
Intonation mathematically correct (Bass: C ; Melody: C)