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Absolute threshold The minimum detectable level of a sound in the abscence of any other external sounds
Amplitude The instantaneous amplitude of an oscillating quantity is its value at any instant, while the peak amplitude is the maximum value that the quantity contains
Audiogram A graph showing absolute threshold for pure tones as a function of frequency. It is usually plotted as hearing loss in dB as a function of frequency, with increasing loss plotted in the downward direction
Aural harmonic A harmonic generated in the auditory system


Bandwidth A term used to refer to a range of frequencies
Basilar membrane A membrane inside the cochlea which vibrates in response to sound and whose vibrations lead to activity in the auditory pathways
Beats Periodic fluctuations in peak amplitude which occur when to sinusoids with slightly different frequencies are superimposed
Bel A unit for expressing the ratio of two powers. The number of Bels is the logarithm to the base 10 of the power ratio
Best frequency See Characterisitc frequency
Binaural A situation involving listening with two ears
Binaural masking level difference (BMLD or MLD) This is a measure of the improvement in detectability of a signal which can occur under binaural listenting condidtions. It is the difference in threshold of the signal (in dB) for the case where the signal and the masker have the same phase and level relationships at the two ears and the case where the interaural phase and/or level relationships of the signal and masker are different


Categorical perception A type of perception where stimuli can only be distinguished if they are identified as belonging to a different category
Characteristic frequency (CF) The frequency at which the threshold of a given single neuron is lowest i.e. the frequency at which it is most sensitive
Combination tone A tone perceived as a component of a complex stimulus which is not present in the sensations produced by the constituent components of the complex when they are presented alone
Complex tone A tone composed of a number of sinusoids of different frequencies
Co-modulation masking release (CMR) The release from masking which can occur when the components of a masker have the same amplitude modulation pattern in different frequency regions
Component One of the sinusoids composing a complex sound, also called a frequency component
Cycle That portion of a periodic function that occurs in one period


Decibel One-tenth of a Bel, abbreviated dB. The number of dB is equal to ten times the logarithm of the ratio of two intensities, or 20 times the logarithm of the ratio of two amplitudes or pressures
Dichotic A situation in which the sounds reaching the two ears are not the same
Difference limen (DL) Also called the just-noticeable difference (JND) or the difference threshold. The smallest detectable change in a stimulus
Diotic A situation in which the sounds reaching the two ears are the same
Diplacusis Binaural diplacusis describes the case when a tone of fixed frequency evokes different pitches in the left and right ear


Envelope The envelope of any function is the smooth curve passing through the peaks of the function
Equal-loudness countours Curves plotted as a function of frequency showing the sound pressure level required to produce a given loudness level
Equivalent rectangular bandwidth (ERB) The ERB of a filter is the bandwidth of a rectangular filter which has the same peak transmission as that filter and which passes the same total power for a white noise input
Excitation pattern A term used to describe the pattern of neural activity evoked by a given sound as a function of the characteristic frequency (CF) of the neurons being excited


Filter A device which modifies the frequency spectrum of a signal, usually while it is in electrical form
Formant A resonance in the vocal tract which is usually manifested as a peak in the spectral envelope of a speech sound
Free field A field or system of waves free from the effects of boundaries
Frequency For a sine wave the frequency is the number of periods occuring in one second. The unit is the cycles per second, or Hz. For a complex periodic sound the term 'repetition rate' is used to describe the number of periods per second (p.p.s.)
Frequency threshold curve See Tuning curve
Fundamental frequency The fundamental frequency of a periodic sound is the frequency of that sinusoidal component of the sound that has the same period as the periodic sound



Harmonic A harmonic is a component of a complex tone whose frequency is an integral multiple of the fundamental frequency of the complex
Hertz A unit of frequency equal to one cycle per second (Abrv. Hz)


Intensity Intensity is the sound power transmitted through a given area in a sound field. Units such as watts per square meter are used. The term is also used as a generic name for any quantity relating to amount of sound, such as power or energy, although this is not technically correct




Level The level of a sound is specified in dB in releation to some reference level. See Sensation level and Sound pressure level
Linear A linear system is a system which satisfies the conditions of superposition and homogeneity
Loudness This is the intensive attribute of an auditory sensation, in terms of which sounds may be ordered on a scale extending from quiet to loud
Loudness level the loudness level of a sound, in phons, is the sound pressure level in dB of a pure tone frequency 1kHz which is judged by the listener to be equivalent in loudness


Masked audiogram See Masking pattern
Masking Masking is the amount (or the process) by which the threshold of audibility for one sound is raised by the presence of another (masking) sound
Masking level difference (MLD) See Binaural masking level difference
Masking pattern This is a graph of the amount of masking (in dB) produced by a given sound as a function of the frequency of the masked sound
Modulation Modulation refers to a periodic change in a particular dimension of a stimulus
Monaural A situation in which sounds are presented to one ear only


Noise Noise in general refers to any unwanted sound. White noise is a sound whose power per unit bandwidth is constant, on average, over the range of audible frequencies. It usually has a normal (Gaussian) distribution of instantaneous amplitudes


Octave An octave is the interval between two tones when their frequencies are in the ration 2:1


Partial A partial is any sinusoidal frequency component in a complex tone. It may or may not be a harmonic
Period The period of a periodic function is the smallest time interval over which the function repeats itself
Periodic sound A periodic sound is one whose waveform repeats itself regularly as a function of time
Phase The phase of a periodic waveform is the fractional part of a period through which the waveform has advanced, measured from some arbitrary point in time
Phase-locking This is the tendency for nerve firings to occur at a particular phase of the stimulating waveform on the basilar membrane
Phon The unit of loudness level
Pitch Pitch is that attribute of auditory sensation in terms of which sounds may be ordered on a musical scale
Psychophysical tuning curve (PTC) A curve showing the level of narrow-band masker needed to mask a fixed sinusoidal signal; plotted as a function of masker frequency
Pure tone A sound wave whose instantaneous pressure variation as a function of time is a sinusoidal function, also called a simple tone



Recruitment This refers to a more rapid that usual growth of loudness with increase in stimulus level, which occurs in certain types of hearing disorders
Residue pitch Also known as virtual pitch, low pitch and periodicity pitch. The low pitch heard when a group of partials is perceived as a coherent whole.


Sensation level This is the level of a sound in decibels relative to the threshold level for that sound for the individual listener
Simple tone See Pure tone
Sine wave, Sinusoidal vibration A waveform whose variation as a function of time is a sine function. This is the function relating the sine of an angle to the size of the angle
Sonification the use of nonspeech audio to convey information; more specifically sonification is the transformation of data relations into perceived relations in an acoustic signal for the purposes of facilitating communication or interpretation
Sound pressure level This is the level of a sound in decibels relative to an internationally defined reference level. The latter corresponds to an intensity of 10-12 W/m2, which is equivalent to a sound pressure of 20 microPa
Spectrum The spectrum of a sound wave is the distribution in frequency of the magnitudes (and sometimes the phases) of the components of the wave
Spike A single nerve impluse or action potential


Timbre Timbre is that attribute of auditory sensation in terms of which a listener can judge that two sounds similarly presented and have the same loudness and pitch are dissimilar. Put more simply, it relates to the quality of a sound
Tone A tone is a sound wave capable of evoking an audiotory sensation having pitch
Tuning curve For a single nerve fiber this is a graph of the lowest sound level at which the fiber will respond, plotted as a function of frequency, also called a frequency threshold curve (FTC)



Virtual pitch See Residue pitch


Waveform Waveform is a term used to describe the form or shape of a wave. It may be represented graphically by plotting instantaneous amplitude or pressure as a function of time