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Alisha is a college music educator specializing in historic and world music studies.
Pitch is the quality that allows us to classify a sound as relatively high or low. Pitch is determined by the frequency of sound wave vibrations. However, frequency is a precise scientific unit of measurement, while pitch, although defined by its frequency, also has a subjective component that takes into account the relative placement of the frequency within the context of an established tuning system and in relation to other frequencies.
Sound is created by vibrations. If you strum a string on a guitar, the motion of your hand against the string will set the string in motion, causing it to vibrate. This vibration creates a musical sound, which, if uninterrupted, will continue until the vibration of the string eventually stops and the sound fades away.
If, however, you strum the guitar and immediately put your hand on the string to stop its vibration, the sound also stops immediately. That sound that you hear is traveling through the air in regular waves, generated by the movement of the vibrating object - in this case, the guitar string.
The fluctuation of these waves, called oscillations, can be measured by the number of wave cycles per second. It is this measurement that is referred to as the frequency of the sound. Frequency is quantified using a unit of measurement known as hertz (abbreviated Hz), which defines the number of repeating cycles per second. For example, if an event happens once per second, it will have a hertz number of one. Therefore, the faster the oscillations of the sound waves, the higher the hertz number, and the higher the pitch.
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In general, smaller vibrating objects produce higher pitches and bigger vibrating objects produce lower pitches.
A definite pitch is a musical sound that has a steady and measurable frequency and can be assigned a hertz number. The sound waves of definite pitches move in a repetitive and evenly-paced pattern with a constant distance between the peaks and valleys of each wave.
Hertz numbers are useful because they provide the basis for a universal tuning system. Using hertz numbers as a measurement, a note on a piano in China and a note on a piano in Chicago can both be tuned to precisely the same frequency. Before scientists were able to measure sound waves, the tuning of musical instruments varied widely from one region to the next. Instruments were mainly tuned to each other, not to an absolute standard.
Today, the universal tuning standard for most musical instruments is a definite pitch with a hertz number of 440. This means that the vibrations of that pitch are oscillating at 440 cycles per second, or 440 Hz. In music, definite pitches such as this are called tones. Tones form the basis of most musical scale systems. Although there are thousands of frequencies in the audible sound spectrum, many musical notation systems, including the Western system, use definite pitches that are determined based on a musical ratio called the octave.
An octave is the distance between two tones, one of which has a hertz number that is double the frequency of the other. For example, if we take 440 Hz and double the frequency, we get a tone with a hertz number of 880. This 2:1 ratio defines the octave. The second tone, which is the octave of the first tone, is created by faster vibrations and generates a higher pitch than the one vibrating at 440 cycles per second. The two tones in an octave sound very similar. In fact, when they are played at the same time, they blend together, which can make it difficult for an untrained musician to recognize them as two distinct tones rather than the same pitch, despite the fact that one is vibrating twice as fast.
Western music theorists have divided the octave into 12 definite pitches of relatively equal distance. Letter names from A-G are assigned to seven of these pitches for notation purposes, with notes that are an octave apart sharing the same letter name to indicate the special relationship between their frequencies. The remaining five pitches are defined by modifying the letter names of pitches A-G by adding the word 'sharp' to indicate a higher pitch, written as a # sign, and 'flat' to indicate a lower pitch, written as 'b.' This system results in some overlap, with certain pitches being the raised form of one pitch and the lowered form of another. For instance, the pitch that lies between D and E can be written as 'D-sharp' or 'E-flat.'
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When these pitches are written on a sheet of music, they are arranged on a musical staff, which is a series of lines and spaces that indicate to performers which pitch should be played. The keyboard note letter names and corresponding hertz numbers shown above can be seen in notated form on the staff below. In general, the higher a note is positioned on the page, the higher the corresponding pitch.
Some sounds, even musical sounds, are not tones. The vibrations of these sounds do not travel in regular, steady patterns but rather move in irregular waves. These sounds cannot be quantified by a single hertz number and are called indefinite pitches. These types of pitches are not assigned a letter name because their vibrations encompass a range of frequencies. Examples of indefinite pitch instruments include many non-pitched percussion instruments, such as the snare drum and cymbals.
While frequency is a specific, measurable, scientific term, pitch is subjective and relative. Humans perceive pitch within the context of other pitches. For example, if you strum the thinnest string on a guitar or strike a note to the far right of a piano keyboard, you will hear a relatively high pitch. If you strum the thickest guitar string or play the key farthest to the left on a piano keyboard, you will hear a relatively low pitch. However, it's important to remember that this 'lowness' is a relative concept.
The lowest tone possible on the piano has a much lower hertz number than the lowest possible tone on a guitar, but each are considered to be low within the context of the range of the instrument. For instance, the guitar string, a low 'E,' has a hertz number of 82.41, while the lowest piano pitch, a low 'A,' has a hertz number of 27.5. Therefore, the low guitar string is relatively high as compared to the lowest piano key.
Although instruments of indefinite pitch do not have a specific frequency, they can also be comparatively high or low based on their frequency range. For example, a cymbal has a generally higher sound than a bass drum.
Pitch refers to the quality of sound that we identify as being relatively high or low. There are two types of pitch: definite pitch, which is created by regular sound wave oscillations, and indefinite pitch, created by irregular sound waves. Definite pitches are called tones and are measured in terms of their frequency, which is a scientific calculation of the number of cycles per second. This calculation provides the hertz number of the frequency, a measurement that can be used to standardize the tuning of musical instruments.
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