What is Perfect Pitch?

What is perfect pitch? To be able to recognize or recreate a musical note at will, you must possess perfect pitch, also called absolute pitch. The ability allows a musician to perform many skills, including tuning an instrument, singing any note at will, or transcribing very quickly and in the correct key. Although the ability is quite rare (about 1 in 10,000), many musicians who have it are adept at both identifying and recreating notes.

The Theory of Perfect Pitch

The important question, which was never given enough attention until now, is not that of “what?” but the question of “how?”. How is it that a small proportion of people are able to notice a supposed elusive “quality” of each note, which most of us cannot? What are these differences and how does perfect pitch really work? Most people can perform quite amazing feats of aural recognition, such as recognizing the characteristics of many different friends' voices and some great musicians do not have perfect pitch. So, why can't we hear the tone qualities between different notes?

We need to be aware of some of the basics of acoustics before we can answer these questions. To begin with, all tonal sounds, such as musical instruments or voices, comprise fundamental frequencies and harmonics. Another name for harmonics are overtones. These are always in all tonal sound. Even if a single sine wave tone is generated and output to a speaker, there will be harmonics in the sound. Waves have a physical property that they create more waves. The harmonics of a tone are multiples of the fundamental frequency. The sound you hear when a single A440 note is played is a combination of 440 Hz, 880 Hz, 1320 Hz, 1760 Hz, 2200 Hz, etc. Usually the fundamental (440 Hz) has the most energy, the second harmonic (880 Hz) has less, and the general trend is a decrease in volume as you count up the harmonics, although some instruments do take exception to this. The “first overtone” is the same as the second harmonic.. To avoid the confusion about this, I will use the harmonic terminology only.

Each instrument has its own harmonic levels, or “spectrum”. If you look at the spectrum for a clarinet, you see that each even harmonic is weak, whereas the odd ones are higher. By contrast, a guitar has a high second, sixth, and seventh harmonics and a lower fundamental.

Obviously, the harmonic spectra are different. The instruments do not sound alike at all. It is the levels of the harmonics of tonal sound, which (along with components of noise) give the particular timbre to the sound. We can easily tell the difference between a flute and a saxophone because they have very different harmonic spectra.

In summary, the unique “quality” or timbre of a tonal sound is always determined by its harmonic levels.

Getting back to the subject of perfect pitch, we know that musicians who have perfect pitch hear differences in “quality”, we might even say timbre, between the notes. We know a composer might choose the key of E flat for a sorrowful piece and F sharp for something more jubilant. So how does this fit in with the harmonic spectra of the notes when we know this to be determined by the instrument? Well, the shocking, but obvious truth is that there is no physical difference in “quality” between the different notes. It only takes a moments' thought to realize that any actual difference would have been measured a long time ago and the mystery of perfect pitch would be no more. It is the human ear, which is responsible for perfect pitch, and the differences between notes are only perceived because of the resonances and frequency response of the ear.

Just like a microphone, the ear is better at hearing some frequencies than others and has moving parts, which have resonances. Tonal sounds contain many frequencies and they will all affect the ear differently. The result is that we perceive some frequencies as much louder than others when, in fact, they have the same physical loudness.

An Equal Loudness curve shows the frequency response of the ear, which is much the same for everyone. The most sensitive frequency is 4000 Hz. A sound of 30 Hz must be almost a million times as powerful to be perceived the same.

A series of resonating components make for resonances in the ear. There is a resonance at about 3000 Hz due to the auditory canal. Resonances also come from the eardrum vibration, bones of the middle ear, and the complicated movements of the cochlea.

The equal loudness curve demonstrates just how varied the response of the ear is to different frequencies but is not the whole story. There are many other phenomena going on when the ear is subjected to multiple frequencies, which is just about all the time. For example, when one frequency masks another and how this depends greatly on the values of these frequencies.

So What is Perfect Pitch?

In summary, the perceived difference in harmonic spectra between the notes of the scale is at the root of perfect pitch. First, there exists the actual harmonic levels of the sound. Then there is a perceived spectrum resulting from the response of the ear. People who have perfect pitch are able to hear the harmonic resonances coming form the frequency response of the ear. Musicians are, generally, much more concerned about the fundamental frequencies of the tones and less so with harmonics, which is why perfect pitch is so rare. To hear with perfect pitch, you need to be able to listen to the harmonics, which is a skill like any other and can be learned until it is second nature.