Pitch is a fundamental aspect of sound, allowing us to distinguish between high and low notes. It is the quality that enables us to arrange sounds on a scale from lower to higher. Understanding pitch is central to how we perceive the auditory world.
Frequency: The Core of Pitch
Sound travels through a medium, such as air, as waves. These sound waves are vibrations that propagate through the material. The number of wave cycles passing a fixed point in one second defines the sound’s frequency.
Frequency is measured in hertz (Hz), with one hertz equaling one cycle per second. A higher frequency indicates more cycles per second, while a lower frequency means fewer cycles. This directly determines perceived pitch: higher frequencies correspond to higher pitches, and lower frequencies result in lower pitches.
It is important to differentiate pitch from loudness. While pitch is determined by frequency, loudness relates to the amplitude of the sound wave, which is the intensity or strength of the vibration. A sound can be high-pitched and soft, or low-pitched and loud, showing these two qualities are distinct.
Producing Pitch from Different Sources
Sources generate sounds with specific frequencies based on their physical properties. In musical instruments, string length, tension, and thickness are primary factors. On string instruments like guitars or violins, shorter, thinner, or more tightly stretched strings vibrate faster, producing higher pitches. Conversely, longer, thicker, or looser strings vibrate slower, resulting in lower pitches.
Wind instruments, such as flutes or trumpets, produce sound by vibrating an air column within them. The length of this air column directly influences pitch. Shorter air columns generate higher frequencies and higher pitches, while longer columns create lower frequencies and lower pitches. Musicians change the effective length of the air column by opening and closing holes or using valves.
The human voice determines pitch using vocal cords. These folds of tissue in the larynx vibrate as air passes through them. Muscles adjust the length and tension of the vocal cords, enabling a wide range of pitches. When vocal cords are stretched and thinned, they vibrate faster for higher pitches; when shortened and thickened, they vibrate slower for lower pitches.
How We Hear and Understand Pitch
The perception of pitch begins in the ear, specifically within the cochlea, a spiral-shaped structure in the inner ear. When sound waves enter the ear, they cause vibrations transmitted to the fluid inside the cochlea. This fluid movement creates pressure waves along the basilar membrane, a flexible structure running its length.
Different sections of the basilar membrane respond most vigorously to different frequencies. High-frequency sounds cause vibrations near the base of the cochlea, while low-frequency sounds stimulate the membrane closer to the apex. Hair cells along this membrane convert mechanical vibrations into electrical signals. These signals are transmitted via the auditory nerve to the brain, where they are interpreted as pitches.
The typical range of human hearing spans from approximately 20 hertz to 20,000 hertz, though sensitivity to higher frequencies often decreases with age.