Last week, I introduced you to the water spirit Ondine, main character of Ravel’s eponymous work. I also mentioned at the end of this short introduction I will talk today about the German physicist Hermann Ludwig Ferdinand von Helmholtz, the author of the classic study of acoustic science. I’m not very sure you are familiar with this great guy. He discovered several things but what makes him interesting to me is his strong interest in physics of perception, and especially his On the Sensations of Tone as a Physiological Basis for the Theory of Music published in 1863. What’s in it? Roughly, he discovered harmonics and their importance. Not following me?

Each sound is the result of a vibration and consist of sine wave shaped oscillations. Sounds produced by an acoustic instrument or by singing consist of a fundamental frequency and overtones that are multiples of the frequency of the first harmonic. These multiples as a whole is called the harmonic series (see fig. below).

The human ear usually doesn’t perceive harmonics as separate notes. A musical tone composed of many harmonically related frequencies is perceived as one sound, the quality, or timbre of that sound being a result of the relative strengths of the individual harmonic frequencies. The timbre of an instrument is thus defined by its harmonic spectrum. For example, the characteristic timbre of a clarinet is a result of its very weak even (4th, 6th, 8th, …) harmonics.

Why did I say I would talk about Ravel if I don’t? Here it comes! We’re speaking about timbre, a synonym for color, the most important thing in Ravel’s Gaspard de la nuit. I am about to reveal a well guarded secret: how Ravel literally creates new sophisticated colors with a single instrument called piano.

Remember the beginning of Ondine reproduced above? The “tremelo” is clearly a color pattern: Ravel doesn’t want us to detail each of the thirty-second notes but to give the illusion of a general color. He uses a C sharp major triad and adds a minor 6th (A). The key is C sharp Major, fundamental tone is C sharp, the C sharp major triad in C Sharp major represents the 4th,5th and 6th harmonics of the C sharp spectrum, nothing unusual. That would have been totally boring if Ravel had not added the minor sixth, the 13th harmonic of the C sharp spectrum. So, basically Ravel took the fundamental tone C sharp, and modify the color of this C sharp by reinforcing certain harmonics in his spectrum. But why adding the 13th harmonic?

First, he added the minor sixth to make the C# triad unstable and create movement. For me, this tremelo is an evocation of liquidity: a general pattern in motion with micro modifications sounds to me like flowing water. But he could have done this in other ways. Why precisely this 13th harmonic?

Acoustics specialists noticed that we reinforce the thirteenth harmonic in our voice to create a compassionate and loving tone. Have you ever noticed the shift in timbre when you speak to someone lovingly with great inner empathy? Putting emphasis on the 13th harmonic creates for the listener a feeling of warmth, comfort, kindness and presence. Exactly what Ravel wants to convey in the beginning of Ondine. Fascinating, isn’t it?

Balancing harmonics is the secret of the timbre: without this 13th harmonic, this beginning would have been totally blend. With a pattern consisting in four tones of the a single spectrum, Ravel created a color exactly matching the ambiance of Aloysius Bertrand’s poem. That’s genius.