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last updated: 10/22/2010

Glossary

Amplitude: the distance that a waveform is displaced from its resting or zero point, generally measured in volts. Amplitude results in the sensation of loudness, measured in decibels.


Aperiodic: the quality of vibrating irregularly. Aperiodicity is a property of noise, or any sound of indiscernible pitch. (See Periodic)


Beating: the waxing and waning in loudness, or regular amplitude modulation, of a sound produced by the combination of two tones very close in frequency.


Chorus Effect: the phenomenon occurring which several sound sources attempt to produce tones in unison; because natural sources will be incapable of achieving a precise matching of pitches, the tones of all sources will be close enough to each other to produce a beating between the corresponding harmonics of each tone. (See Beating).


Coupling: the physical connection between a vibrating body (e.g., a string, air column, or membrane) and a resonator (e.g., the body of a violin, flute, or drum). The nature of the coupling on an instrument determines the stability of the timbre over the instrument's pitch range. In a tightly coupled system, the vibrations of the vibrating column and those of the resonator influence each other, so that as the pitch changes (and the vibrations of the column change), the timbre changes (the vibrations of the resonator change). In a loosely coupled system, the vibrating column and the resonator vibrate independently, so that pitch can change without effecting the timbre; therefore in a loosely coupled system, the timbre stays relatively constant over the entire pitch range.


Decay: the process by which a tone fades from its loudest point to a point of inaudibility. Acoustically, decay is the process by which a tone goes from its highest to zero amplitude.


Drone: a tone of steady pitch that underlies or overlays other tones which are moving in pitch, perhaps producing a melody.


Frequency: a measure of the cycles or numbers of vibrations per second of a vibrating object. Frequency (cycles per second) is measured in Hertz. For example, an instrument playing an A 440 is producing 440 cycles per second, or 440 Hz. Generally speaking the frequency of a sound cooresponds to its pitch.


Fundamental Frequency: the lowest harmonic produced by a periodic sound, generally corresponding to the sound's pitch.


Harmonic: 1) noun: one of a theoretically infinite number of frequencies produced by a sound source. The cycles per second, or frequency, of each harmonic must be a multiple of the frequency of the lowest harmonic, or fundamental frequency. The cycles per second of the fundamental frequency generally corresponds to the pitch of the sound, while the relative amplitudes of the other harmonics determine the steady state timbre of the sound. 2) adjective: the quality of a harmonic which is in "harmonic relation" with other harmonics, that is which has a frequency that is a multiple of the fundamental frequency; e.g., a harmonic of frequency 1000 Hz is in harmonic relation with harmonics of frequencies 200 Hz, 300 Hz, 400 Hz, all of which are harmonics of the fundamental frequency 100 Hz.


Harmonic Structure: acoustic structure; a sound's harmonic elements at their relative amplitudes.


Impulsive Tone: a tone produced by a single stimulation of a vibrating column (e.g., a string, air column, or membrane) by which all harmonics of the tone are excited, then left to decay to zero at individual rates. Examples of impulsive tones are produced by percussive instruments or plucked instruments. If the harmonics of an impulsive tone decay at different rates of speed, the timbre of the sound can be said to change over the duration of the tone.. (See Sustained Tone).


Inharmonic: the quality of being out of harmonic relation with a fundamental frequency or any of its harmonics; e.g., a harmonic of frequency 1005 Hz is inharmonic among, or not in harmonic relation with harmonics of frequencies 100 Hz, 200 Hz, 300 Hz, 400 Hz, etc.


Jitter: a measure of pitch waivering (either micromodulation or vibrato) achieved by a tone attempting a steady state.


Lamel: a key or plank by which certain percussive instruments are played; for example, the key of a xylophone or a piano.


Micromodulation: the minute, often involuntary, waivering in pitch produced by a natural source attempting a steady state on a pitch.


Millisecond: one one-thousandth of a second (abbrev. ms).


Mirleton: device attached to an instrument's resonator to produce extra noise; generally the vibrations of the resonator act on the mirleton to produce a noise which fuses with other timbral elements.


Periodic: the quality of vibrating in regular cycles, resulting in a sound of definite pitch and timbre. (See Aperiodic)


Pitch Inventory: the collection of all pitches which an instrument can produce or which an instrument uses in playing a particular piece of music.


Resonator: the body of an instrument, or any device to which the vibrating column (e.g., a string, air column, or membrane) is attached. The resonator acts like a filter on the harmonics of the vibrating column, so that some of the harmonics are amplified, some attenuated. The interaction of the source vibrating column and the resonator produces an instrument's characteristic timbre.


Rise Time: the time required for a tone to reach the intensity (loudness) of its steady state.


Source Wave: the original vibration produced by stimulating action on a vibrating column (e.g., a bowed string), which will pass through the resonator (e.g., the body of a violin) to produce a tone with timbre; also called source vibration.


Source-Filter Transfer: the process by which a source wave passes through a resonator producing a timbred tone. (See Transfer Function).


Spectral Envelop: a description of a instrument's timbre at a specific moment, created by connecting all the harmonics of a spectrum.


Spectrogram
: two-dimensional visual respresentation of sound, plotting frequency against time; amplitude is indicated only approximately by brightness of color contrast (in a colored spectrogram) or darkness of gray-scale (in a black and white spectrogram).


Spectrum
: two-dimensional visual respresentation of sound, plotting frequency against amplitude; since time is not represented in a spectrum, the image shows individual harmonic components of a sound with their relative amplitudes at a single moment of time. Since timbre is determined in part by the relative amplitudes of harmonics, a spectrum constitutes the best representation of a instrument's timbre at a specific moment.


Strike Tone: for a percussive instrument (e.g., the xylophone), the sound made by the impact of the striking implement against the vibrating body, as distinct from the sound produced by the combination of the vibrating column and resonator.


Sustained Tone: a tone produced by the continuous stimulation of a vibrating column, in which all harmonics remain constant as long as the stimulation continues constant. Examples of sustained tones are those produced by bowed or blown instruments. In a sustained tone, the timbre stays constant for the duration of the tone. (See Impulsive Tone).


Temporal Envelop: a plotting of the amplitude of a harmonic component over time; can also plot the amplitude of an entire sound over time.


Timbre: 1) the characteristic tone quality of an instrument (e.g., the timbre of a flute v. the timbre of a violin); sometimes defined as any part of a sound other than pitch or loudness. 2) one of several tone qualities produced by a single instrument (e.g, a dark tone v. a bright tone). In both cases 1) and 2), timbre is produced in part by the relative amplitudes of an instrumental tone.


Transfer Function: the process by which a source wave passes through a resonator producing a timbred tone.


Unison: tones produced by several different sources all on the same pitch.


Vibrato: the deliberate pitch movement of a tone around a central pitch, also called frequency modulation.


Waveform: a visual representation of a sound wave, showing the course of the wave over time, and providing some information about the loudness of a sound over time as determined by the height of the waveform.



last updated: 10/22/2010