Every sound we hear has two qualities: pitch and timbre. Pitch is determined by the frequency of the sound wave, while timbre is the harmonic spectrum overlaying the fundamental waveform. These two qualities allow us to differentiate between sounds. For example, the organ, an ancient instrument, uses pipes of different lengths to produce sounds of varying pitches. The timbre of a sound is influenced by its harmonic series, which is unique to each sound. This understanding of sound differentiation extends to our own voices, each with its unique harmonic fingerprint. By being aware of the sounds around us, we can appreciate the rich tapestry of sound in our world.

Every sound - that of a bird chirping, or the wind raging, a Stradivarius violin or my voice telling you this  has two qualities: pitch, determined by the frequency of the wavelength, and timbre, the harmonic spectrum overlaying the fundamental waveform. 

We can use the pipe organ to exemplify these concepts. The organ was invented by a Greek engineer in the 3rd century before the Common Era, Ctesibios.   

The pipes on an organ are of different lengths, with the longest ones making the lowest sounds, that is, producing sound waves of lower frequency; and the shorter ones making higher sounds, producing soundwaves of higher frequency.

And as the instrument developed, the range of pitches increased dramatically, so that one organ might contain extremely long pipes, sounding barely within the range of human hearing, as well as extremely small pipes, the size of a baby’s finger, producing pitches so high that only people under 40 (and dogs!) can hear them.

Hearing high and low frequencies is fairly straightforward, but how do we know if we’re hearing a jackhammer or a gong, a baby’s cry or a saxophone, a nightingale or a flute? 

Each sound has its own unique tone color or timbre. Even if it’s sometimes hard to describe, most people can readily hear whether a note is played on a piano or on a violin, or if there’s thunder during a rainstorm. All the variables of sound production lead to differently shaped soundwaves.

To understand this better, we need to learn about harmonics. When a pipe or string vibrates along its full length, this is the first harmonic. But a vibrating body does not just vibrate along its full length but also in halves, thirds, fourths, fifths and so on. At half its total length, this creates the octave, the second harmonic. When it vibrates in thirds, this creates the interval of a fifth above the octave, the third harmonic. When it vibrates in fourths, you guessed it, we get the octave above the octave, the fourth harmonic. 

All sounds have a specific harmonic series that features these harmonics: at the octave, the fifth above that, the superoctave, the major third above that, and so on… the relative strengths of these harmonics is what creates the distinctive timbre of each sound, whether it be a cat meowing or a pianist playing.

Each tone color has a sonic fingerprint created by the relative strengths of the harmonics.  When the full-length vibration is very strong compared to the harmonics, the fundamental pitch is predominant. A tuning fork is a good example of this. It has no strong upper harmonics affecting its sound wave; we want a tuning fork to give a strong fundamental to which we can tune our voice or an instrument. If there were strong harmonics at other frequencies, the pitch for tuning would not be as clear. Similarly the main sound of an organ, called the Principal, emphasizes the fundamental.

But other sound waves have stronger harmonics and this creates distinctive timbres.  Listen to this sound, produced by a reed vibrating inside an organ pipe. The resonator of this pipe emphasizes some of the harmonics, giving a very bright, buzzy timbre.

And this flute pipe is capped, which halves the wavelength, making it sound an octave higher than it would if it were open at the top. Because of the closed top of the pipe, only the fundamental odd-numbered harmonics are produced, giving it a more hollow timbre.

The different strength of harmonics produces an amazing tapestry of sound. And this extends to our own voices, each with its distinctive fingerprint of harmonics.