GLOSSARY OF ACOUSTICS Taken from http://www.music.mcgill.ca/auditory/glossary.html Absolute pitch Comparatively rare ability to identify any musical note, or to produce orally any named note. Acoustic energy Variation in air pressure produced by the vibration of an object Amplitude of a sound wave Maximum pressure variation, a force per unit area measured in Newtons per square meter. Analytic listening Listening for the pure tone components of a complex tone, as opposed to holistic (synthetic) listening. Audiogram Graph of threshold intensity for hearing pure tones as a function of frequency. Auditory cortex Region of the cortex devoted to the analysis of sound information Auditory nerve Bundle of nerve fibres which carries information from the cochlea to the higher stages of the auditory system. Auditory stream Sequence of sounds grouped together because they are attributed to the same source (sonic event). Note that Warren uses the term "parallel auditory continua". ---------------------------------------------------------------------------- B-C ---------------------------------------------------------------------------- Basilar membrane A membrane inside the cochlea which vibrates in response to sound. It is here that sound energy is converted into neural impulses. Chord Three or more notes sounded simultaneously. Chroma Musical note name, without specification of the octave register. Chromatic scale A scale of twelve equal steps per octave, each step being a semitone. Cochlea A coiled, fluid-filled chamber in the inner ear, containing the basilar membrane, where mechanical (sound) energy is converted into neural energy. Resolution of a complex sound into its components occurs in the cochlea. Complex tone A tone composed of a number of sinusoids at different frequencies and phases (not necessarily harmonic). Component One of the sinusoid that is part of a complex sound. Cycle That part of a periodic function that occurs in one period. ---------------------------------------------------------------------------- D-E-F-G ---------------------------------------------------------------------------- Difference threshold Minimum amount by which stimulus intensity must be changed in order to produce a just noticeable change in sensation. Equal loudness contours Curves plotted as a function of frequency, showing the sound pressure level required to produce a given loudness level. Envelope The envelope of a function is a smooth curve passing through the peaks of the function. eg. spectral envelope. FFT Fast Fourier Transform. A specific efficient spectral analysis program. Formant A resonance in the vocal tract, which causes a peak in the spectral envelope of a speech sound. Frequency For a sine wave, the frequency is the number of repetitions per unit of time. 1 cycle per second = 1 hertz. Usually referred to in kHz, or number of repetitions per msec. Fundamental Lowest component of a harmonic complex tone. Fundamental frequency The fundamental frequency of a periodic sound is the frequency of repetition of the waveform. ---------------------------------------------------------------------------- H ---------------------------------------------------------------------------- Habituation The process by which an organism ceases to respond to some recurring or familiar stimulus. Harmonic A component of a complex tone, whose frequency is an integral multiple of the fundamental frequency of the complex. The third harmonic is at the frequency 3f, where f is the fundamental frequency. Harmonic complex tone Complex tone whose partials are all harmonics ie. all partials have frequencies that are integral multiples of the fundamental frequency. Harmonic complex tones are periodic. Hear out Hear, by careful analytic listening, the components of a complex tone. hertz Unit of frequency. 1 Hz = 1 cycle per second. Holistic listening Normal mode of perceiving the whole without being aware of the components of a complex tone. Opposite of analytical. Also called synthetic. ---------------------------------------------------------------------------- I-J-K-L-M-N-O ---------------------------------------------------------------------------- Intensity Sound power transmitted through a given area. Intensity is proportional to the square of the amplitude and, expressed as power per unit area, it is measured in watts per square meter. The threshold of audibility is 10 power -12 W/ sq m. Logarithmic scale A scale in which the logarithm of the raw value is used instead of the raw value. The effect is tat equal steps in the raw value are replaces by equal ratios eg. dB scale. Loudness Attribute of auditory sensation corresponding to intensity. Sounds can be ordered on a loudness scale from quiet to loud. Mel scale A proportional scale, in which equal intervals (measured in mel) correspond to equal perceived interval sizes. The mel scale is roughly proportional to the logarithm of frequency but becomes linear at low frequencies. Noise Usually refers to unwanted sound. Noise is not periodic. White noise is a sound with constant power per unit bandwidth over the audible frequency range. Octave The interval between two tones when their frequencies are in the ratio 2:1. Musical notes an octave apart have the same letter name. Octave-related complex tone Complex tone whose components are separated by octaves. ---------------------------------------------------------------------------- P-Q ---------------------------------------------------------------------------- Partial One of the sinusoidal components that is part of a complex sound. Perfect fifth Interval between the first and fifth degrees of a major scale, or interval between two pure tones whose frequencies are in the ratio 3:2, or 7 semitones. Perfect fourth Interval between the first and fourth degrees of a major scale, or interval between two pure tones whose frequencies are in the ratio 4:3, or 5 semitones. Perfect pitch See absolute pitch. Period The smallest time interval over which a function repeats itself. Periodic sound A periodic sound has a waveform which repeats regularly over time. Phase Relation in time between two pure tones of the same frequency. In phase - both waveforms peak together. Pitch The attribute of auditory sensation by which sounds can be ordered on a musical scale ie. by which sounds can be judged relatively high or low. Pitch ambiguity A sound has pitch ambiguity if holistic perception may yield one of several different pitches depending on attention, context,.. Pitch shifts Change in pitch of a tone due to intensity or masking. Proximity Gestalt principle of organisation referring to the perceptual tendency to group together objects that are near to one another. In the auditory perception, "near" means close in the frequency-time domain. Psychophysics Branch of Perception that is concerned with establishing quantitative relations between physical stimulation and perceptual events. A science which arose in the early part of the twentieth century. Pure tone A tone whose soundwave is sinusoidal. quantitative relations between physical stimulation and perceptual events. ---------------------------------------------------------------------------- R-S ---------------------------------------------------------------------------- Relative pitch Ability to identify a musical interval. An ability which can be learned. Residue pitch Also known as low pitch, virtual pitch, periodicity pitch. Pitch of a complex tone, under normal listening. The name "residue" refers to the phenomenon of the missing fundamental - the pitch perceived comes from the "residue". Salience Perceptual prominence, or likelihood of being noticed. Semitone The notes corresponding to adjacent keys on the piano. The interval that results when the octave is divided into 12 equal intervals. Similarity Gestalt principle of organisation referring to the perceptual tendency to group together objects that are similar in texture, size, shape, pitch, loudness, timbre,... Sine wave A waveform whose variation over time is the sine function. The most efficient form of oscillating motion. Spectral analysis Mathematical analysis of a waveform into sinusoidal components, as by Fourier analysis. Spectral dominance Effect by which the pure tone components in the range 200 Hz to 2000 Hz have the greatest influence on the perception of a complex sound. The spectral dominance function (averaged over many subjects) for pure tones has a broad peak around 700 Hz. Spectrum A spectrum graph shows the power (or amplitude) in each of the component frequencies. ---------------------------------------------------------------------------- T-U-V-W-X-Y-Z ---------------------------------------------------------------------------- Timbre Relates to the quality of a sound. Timbre depends on the frequency and amplitude of partials, and on their evolution over time. Tone A sound wave that evokes a sensation of pitch. Virtual pitch The pitch of a complex tone with synthetic (holistic) listening. See residue pitch. Waveform Waveform of a tone refers to the graph of sound pressure to time. ----------------------------------------------------------------------------