Pitch (music)

Pitch is the auditory quality that allows listeners to judge sounds as "higher" or "lower." It is a major attribute of musical tones, alongside duration, loudness, and timbre. While people often use pitch to order sounds on a musical scale, it is a subjective psychoacoustical attribute. This means pitch is a personal perception rather than a purely objective physical property.

Historically, studying pitch has been a central problem in psychoacoustics. This field examines how the auditory system represents and processes sound. By understanding pitch, scientists can better understand how humans perceive the world through hearing.

To understand the mechanism of pitch, one must distinguish it from frequency. Frequency is an objective, scientific attribute that can be measured in hertz (Hz). One hertz represents one cycle per second of vibration. Pitch is the subjective perception of these sound waves by an individual. High pitch corresponds to very rapid oscillations of the air. Low pitch corresponds to much slower oscillations.

Although they are different, pitch is almost entirely determined by frequency. The intensity, or amplitude, of a wave does not determine its pitch. However, loudness can cause small shifts in perceived pitch. For example, a 200 Hz tone may seem one semitone lower when it is very loud. Above 2,000 Hz, the pitch may seem higher as loudness increases.

Scientists use different theories to explain how the brain processes pitch. One approach is called place theory. This theory suggests that pitch is determined by the specific location of maximum excitation on the basilar membrane in the ear. This is known as tonotopy. Another approach is temporal theory. This theory suggests that pitch is coded by the timing of action potentials in the auditory nerve. Specifically, it may involve the phase-lock of these electrical signals to the frequency of the sound. Researchers continue to debate how these different biological mechanisms work together to create the experience of pitch.

Musical sounds can be categorized as having either definite or indefinite pitch. A sound with a definite pitch has a clear, identifiable note. This happens because the sound has a harmonic frequency spectrum. Every sound produces many simultaneous vibrations called modes. The lowest frequency is the fundamental frequency. The other frequencies are called overtones or partials. If these overtones are integer multiples of the fundamental, they are called harmonics.

Conversely, sounds with indefinite pitch are difficult to identify as specific notes. These sounds often have inharmonicity, meaning their spectra are not harmonic. A snare drum is an example of an indefinite pitch instrument. You cannot easily name its note, but you can still tell it is higher than a bass drum.

There are specific limits to how much pitch a human can perceive. The just-noticeable difference (jnd) is the threshold at which a listener can detect a change in pitch. Below 500 Hz, the jnd for sine waves is about 3 Hz. Above 1,000 Hz, the jnd for sine waves is about 0.6% of the frequency. In the human hearing range, there are approximately 1,400 perceptible pitch steps. This is much larger than the 120 notes found in the standard equal-tempered scale. Some sounds can even create aural illusions. The Shepard scale is a famous example where tones seem to ascend or descend forever.

Because pitch can vary, musicians use a pitch standard to stay in tune. A pitch standard is a conventional reference point for an ensemble. Since 1939, the most common standard has been A440. This means the note A above middle C is set to 440 Hz. However, different eras of music use different standards. Baroque pitch is often set at A=415 Hz. Classical pitch for instruments like the fortepiano might be set at 427 Hz or 430 Hz. Some Romantic era ensembles use 432 Hz or 435 Hz. These standards allow musicians to perform accurately within their specific musical traditions.

Pitch also relates to the concept of transposition in music. Transposing instruments are written in different keys than they actually sound. For example, a clarinet might be written as a C but actually sounds as a B. To avoid confusion, musicians use the term "concert pitch." This refers to the actual sounding pitch of the notes. Understanding these relationships between written notes, physical frequencies, and perceived sounds is essential for both musicians and scientists. It connects the mathematics of physics to the beauty of musical expression.