A musical psychoacoustic demonstration

Before you go on reading, please listen carefully to the following two 2-second piano recordings, and see if you can put your finger on the difference between the recordings.

Most people will hear a difference between the two, perhaps thinking that they were recorded on different instruments, or that the notes are different.

To reveal the actual difference between the two, please scroll down...

The two audio clips above are actually piano recordings from which the first 200 msec have been removed. Here are the original recordings, with those 200 msec included. Can you now tell what the difference between the recordings is?

Browse further down to see the answer...

The first recording is a piano playing a Middle C. The second recording is the same piano playing a Middle C together with a High C (one octave above). Because the base frequnecy and the harmonics of the High C all fall on harmonics of the Middle C, it is not trivial to hear the High C.

This experiment demonstrates the importance of the note onset (the first few hundred milliseconds) in humans’ ability to differentiate between notes. The onset contains nonlinear effects which fade out over time, and these turn out to be important in differentiating notes in a chord.

Recorded and written by Zvika Ben-Haim. This is based on a similar experiment which I saw described in a musical acoustics textbook long ago. Sadly I was unable to find this reference. If anyone is aware of a published source describing this phenomenon, please let me know and I will add a citation here.