Audio Topics

Absolute Pitch
The exact pitch value of a musical note (for example, middle C)
Acoustic Cavity
The acoustics of enclosed volumes are important when considering sound propagation within the volume.
Acoustic Centre
The point in space of the origin of sound.
Acoustic Feedback
Acoustic feedback is the return of acoustic energy from the output of a sound reproducing equipment.
Acoustic Refraction
The process by which the direction of sound propagation is changed due to spatial variation in the speed of sound in the medium.
Acoustic Screen
A moveable screen, usually covered in sound absorbent material on one side and having a reflective surface on the other.
Acoustic Trauma
Damage to the hearing mechanism caused by a sudden burst of intense noise, or by a blast.
Action Level
An action level is basically a noise exposure level at which employers are required to take certain steps to reduce the harmful effects of noise on hearing.
Active Crossover
A loudspeaker crossover requiring power to operate.
Adaptive Differential Pulse Code Modulation
A compression technique which encodes the predictive residual instead of the original waveform signal so that the compression efficiency is improved by a predictive gain.
Adaptive Transform Acoustic Coding
A lossy audio coding system based on psychoacoustic principles.
ADC
Abbreviation of Analogue to Digital converter.
ADPCM
A compression technique which encodes the predictive residual instead of the original waveform signal so that the compression efficiency is improved by a predictive gain.
ALCONS
The measured percentage of Articulation Loss of Consonants by a listener.
Allusive Listening
Allusive listening is a presumed listening mode that may be said to occur where a listener relates moments or features of the music to similar moments or features in other musical works.
Ambience
The acoustic characteristics of a space with regard to reverberation.
Amplitude Distortion
A distortion of the wave shape of a signal.
Anomia
A neurological disorder which causes a marked inability to name otherwise familiar stimuli.
Apical Turn
The final turn in the spiral of the cochlea furthest from the oval and round windows.
Apparent Source Width
Discovered and developed by A. H. Marshall, ASW is a subjective parameter of spaciousness in concert halls, and is related to the level, at the listener's ears, of lateral reflections in the first 50 to 80 milliseconds after the arrival of the direct sound.
Arithmetic Coding
Arithmetic coding removes this restriction by representing messages as intervals of the real numbers between 0 and 1.
Articulation Loss of Consonants
The measured percentage of Articulation Loss of Consonants by a listener.
ATRAC
A lossy audio coding system based on psychoacoustic principles.
Attack
The beginning of a sound; the initial transient of a musical note.
Audio Amplifier
An amplifier designed specifically for amplifying audio signals in the frequency range 20Hz to 20kHz.
Audio Frequency
Generally in the range 20Hz to 20KHz.
Audio Transducer
An electronic device that converts electrical signal variations to sound, such as a loud speaker, or sound to electrical variations, such as a microphone.
Audiogram
Graph of hearing threshold level as a function of frequency.
Audiometer
An instrument for measuring hearing acuity.
Auditory Anomia
A neurological disorder which causes a marked inability to name otherwise familiar acoustic stimuli such as a door bell or motor vehicle.
Auditory Cortex
Region of the cortex devoted to the analysis of sound information.
Auditory Nerve
Bundle of nerve fibers that carry information from the cochlea to the higher stages of the auditory system.
Auralization
The technique of using computer-based mathematical models of an acoustic environment and 3D sound processing methods to make audible the sound field of a source in the modeled space.
A Weighting
This is the most generally used filter when making overall noise measurements.
Axial Mode
The room resonances associated with each pair of parallel walls.
Backward Recognition Masking
The reduction in the ability to recognize a sound pattern due to the subsequent presentation of another sound pattern with similar information content.
Baffle
A movable barrier used to achieve separation of signals from different sources.
Band Reject Frequencies
A tuned circuit that does not pass a specified band of frequencies.
Barany Box
Clockwork noise generator used when necessary as a masker in tuning fork or clinical speech tests.
Bark
The Bark is the standard unit corresponding to one critical band width of human hearing.
Bass
The lower range of audible frequencies.
Bass Boost
The increase in level of the lower range of frequencies, usually achieved by electrical circuits.
Block Companding
Normalising of the digital representation of an audio signal within a certain time period.
Boundary Microphone
A type of microphone that detects sound pressure level changes at a boundary of the acoustic space in order to reduce interference between direct and reflected sound.
Brilliance
In concert hall acoustics, a bright, clear, ringing sound, rich in harmonics, is called brilliant.
B Weighting
The B-weigthing curve approximately follows the 70 phon curve.
CD
Abbreviation of Compact Disc, an optical disc designed to store digitally 74 minutes of stereo audio data.
cdrom
Abbreviation that stands for Compact Disc Read Only Memory.
Chirp
A chirp is a sound that has a rapid increase in frequency.
Chord
A line segment that connects two points of a curve or circle.
Chromatic Scale
A scale consisting of 12 semitones.
Circular Frequency
The frequency of a steady recurring phenomenum in radians per second.
Clarity
In concert hall acoustics, the ratio, expressed in decibels, of the energy in the first 80 milliseconds of an impulse sound arriving at a listener's position divided by the energy in the sound after 80 milliseconds.
Class A Amplifier Operation
The type of operation in which the amplifier is biased so that variations in input signal polarities occur within the limits of cutoff and saturation.
Class AB Amplifier Operation
The type of operation in which the amplifier is biased so that collector current is cut off for a portion of the alternation of the input signal.
Class B Amplifier Operation
The type of operation in which the amplifier is biased so that collector current is cut off for one-half of the input signal.
Class C Amplifier Operation
The type of operation in which the amplifier is biased so that collector current is cut off for more than one-half of the input signal.
Class D Amplifier Operation
A switching amplifier or PWM amplifier, the switches are either fully on or fully off, significantly reducing the power losses in the output devices.
Click
When the duration of a sound is less than a time threshold required for pitch recognition, the sound is heard as a click rather than a tone.
CNEL
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Codec
Acronym for compressor/decompressor.
Community Noise Criteria
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Community Noise Equivalent Level
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Compact Disc
An optical disc designed to store digitally 74 minutes of stereo audio data.
Compander
A combination of a compressor at one point in a communication path for reducing the volume range of signals, followed by an expander at another point for restoring the original volume range.
Compression
A pressing force that squeezes a material together.
Concert Pitch
Established by the International Organisation for Standardisation in 1955, the agreed reference frequency of 440 Hz. for the note called middle A.
Condenser Microphone
A type of microphone in which the diaphragm is one plate of a capacitor containing an electrical charge.
Conductive Hearing Loss
Hearing loss due to the impairment of sound transmission before it reaches the inner ear.
Consonance
Two or more sounds that, when heard together, sound pleasant.
Convolution
Convolution meaning ..intertwined, coiled…
Critical Band
In human hearing, only those frequency components within a narrow band, called the critical band, will mask a given tone.
Crossover
An electrical circuit consisting of a combination of high-pass, low-pass and bandpass filters used to divide the audio frequency spectrum (20Hz to 20kHz) into segments suitable for individual loudspeaker use.
C Weighting
The C-weighting curve approximately follows the 100 phon curve.
DAB
Abbreviation of Digital Audio Broadcasting.
dB
Short for decibel.
dBA
A sound-level meter reading with an A-weighting network simulating the human-ear response at a loudness level of 40 phons.
dBB
A sound-level meter reading with a B-weighting network simulating the human-ear response at a loudness level of 70 phons.
Dead Room
Room characterized by a relatively large amount of sound absorption and a relatively short reverberation time.
Decade
Ten times any quantity or frequency range. The range of the human ear is about 3 decades.
Decibel
The human ear responds logarithmically and it is convenient to deal in logarithmic units in audio systems.
De-Emphasis
Filtering applied to an audio signal after storage or transmission to undo a linear distortion due to emphasis.
Definition of a Sound
This may be described by the time at which the sound arrives at the listening position.
Diagnostic Acceptability Measure
Scores are based on results of test methods evaluating the quality of a communication system based on the acceptability of speech as perceived by a trained normative listener.
Diagnostic Rhyme Test
An intelligibility measure where the subject′s task is to recognize one of two possible words in a set of rhyming pairs.
Dichotic
Listening condition in which different signals are applied to the two ears.
Diffusion
The mixing of two substances caused by random molecular motions.
Digital Audio
The use of sampling and quantization techniques to store or transmit audio information in binary form.
Digital Audio Broadcasting
The transmission of radio signals using digital rather than analogue methods.
Digital Audio Compression
Any of several algorithms designed to reduce the number of bits required for accurate digital audio storage and transmission.
Digital Theatre System
A multi-channel encoding/decoding system. Used in some movie theatres. Also now included in some home-theatre processors.
Digital Versatile Disc
Optical disc used for data, video and audio storage.
Diotically
The same signal at both ears.
Directivity Factor
The ratio of the sound pressure squared, radiated directly ahead of a sound source, to the sound pressure squared radiated in all directions.
Directivity Index
The difference between sound pressure level in any given direction in the acoustic far field and the average sound pressure level in that field.
Discrete Tone
A prominent single frequency component within a broadband noise signal.
Distance Double Law
In pure spherical divergence of sound from a point source in free space, the sound pressure level decreases 6 dB for each doubling of the distance.
Distance Factor
An indication of a directional microphone′s increased working distance.
Dolby Digital
A five-channel system consisting of left, centre, right and left rear, right rear channels. All processing is done in the digital domain.
Dolby Prologic
This is a four-channel sound reproduction system consisting of left, center, right and rear channel, (the single rear channel is usually played through two speakers).
Drumming Noise
Often used to describe noise in the frequency range 30 to 60Hz.
DTS
Abbreviation of Digital Theatre System.
Duct Acoustics
Ducts with acoustic waves propagating through them exist in many forms.
Duplex Theory of Localization
This is the combination of the two methods that describe human binaural sound localization first proposed by Lord Rayleigh around 1900.
DVD
Digital Versatile Disc, optical disc used for data, video and audio storage.
Dynamic Headroom
The ability of an audio device to respond to musical peaks.
Dynamic Microphone
A device in which sound waves move a coil of fine wire that is mounted on the back of a diaphragm and located in the magnetic field of a permanent magnet.
Ear
The human ear, as a sound receiver, has to operate under a wide range of conditions.
Ear Canal
The external auditory meatus; the canal between the pinna and the eardrum.
Eardrum
The tympanic membrane located at the end of the ear canal that is attached to the ossicles of the middle ear.
Early Early Sound
Structure-borne sound may reach the microphone in a room before the airborne sound because sound travels faster through the denser materials.
Earplug
Hearing protector that is inserted into the ear canal.
Echo
A delayed return of sound that is perceived by the ear as a discrete sound image.
Echo Location
Determining the location of a target relative to the sensor face by means of measuring the time it takes for a sound wave to travel to the target and be reflected back to the sensor
Echograms
A record of the very early reverberatory decay of sound in a room.
EES
Early Early Sound
Effective Number of Bits
Figure of merit for an A/D converter describing how many bits of effective resolution, this is below the actual A/D word size.
Effective Perceived Noise Level
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Emphasis
Filtering applied to an audio signal before storage or transmission to improve the signal-to-noise ratio at high frequencies.
Entropy Coding
Variable length lossless coding of the digital representation of a signal to reduce statistical redundancy.
Equal Loudness Contour
A contour representing a constant loudness for all audible frequencies.
Equalization
The process of adjusting the frequency response of a device or system to achieve a flat or other desired response.
Equalizer
A device for adjusting the frequency response of a device or system.
Equivalent Continuous Sound Level
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Euphonic
Pleasing. As a descriptive audio term, usually refers to a coloration or inaccuracy that none-the-less may be sonically pleasing.
Eustachian Tube
The tube running from the middle ear into the pharynx that equalizes middle-ear and atmospheric pressure.
Fidelity
As applied to sound quality, the faithfulness to the original.
Field Sound Transmission Class
The same as STC rating except as measured in the field in accordance with standard methods.
Flanging
The term applied to the use of comb filters to obtain special sound effects.
Free Vibration
Free vibration occurs without forcing, the vibration of a string after it has been plucked.
Frequency Range
The bandwidth of a filter or signal.
Fusion Zone
All reflections arriving at the observer's ear within 20 to 40 msec of the direct sound are integrated, or fused together, with a resulting apparent increase in level and a pleasant change of character. This is the Haas effect.
Graphic Level Recorder
A device for recording signal level in dB vs. time on a tape. The level in dB vs. angle can be recorded also for directivity patterns.
G Weighted Overall Level
This purportedly reflects human response to infrasound.
Haas Effect
Delayed sounds are integrated by the auditory system if they arrive at the ear within 20 to 40 msec of the direct sound.
Habituation
The process by which an organism ceases to respond to some recurring or familiar stimulus.
Hair Cell
Sensory cells in the cochlea which transform the mechanical energy of sound into nerve impulses.
Harmonic Distortion
Distortion of a signal by adding content that is harmonically related to the original signal. Clipping overload of an amplifier adds odd-order harmonics to the signal.
Harshness
A typical transient interdisciplinary phenomenon of noise and vibration.
HDMI
Abbreviation of High-Definition Multimedia Interface.
Headroom
A term related to dynamic range, used to express in dB, the level between the typical operating level and the maximum operating level above which the signal will be clipped.
Hearing Damage
A person exposed to high noise levels can suffer hearing damage. The damage may be gradual or traumatic.
Hearing Range in Animals
Many animals hear a much wider range of frequencies than is possible for humans.
Hearing Sensitivity
The human ear is less sensitive at low frequencies than in the midrange.
Hertz
The SI unit of frequency indicating the number of cycles per second (symbol Hz).
High Pass Filter
A filter that passes signal frequencies above a specific, or cut off, frequency is called a high pass filter.
High-Definition Multimedia Interface
A compact audio visual interface for transmitting uncompressed digital data.
Huffman Coding
For a given character distribution, by assigning short codes to frequently occurring characters and longer codes to infrequently occurring characters, Huffman's minimum redundancy encoding minimizes the average number of bytes required to represent the characters in a text.
Hydrophone
A hydrophone converts acoustic energy into electrical energy and is used in underwater passive systems for listening only.
Hz
An abbreviation of hertz. The SI unit of frequency.
Ideal Driver
A speaker driver that delivers excellent performance in terms of polar response, power handling, efficiency, frequency range and reliability.
Impact Isolation Class
A measure or specification of isolation effectiveness of building structures from impact noises such as slammed doors, dropped objects, footfalls, shuffled furniture, etc. The higher the IIC rating, the better such isolation.
Inner Ear
The inner ear is a labyrinth of twisting fluid-filled passages associated with hearing and balance.
Intensity Stereo
A method of exploiting stereo irrelevance or redundancy in stereophonic audio programmes.
Interaural Level Difference
In binaural hearing the interaural level difference has an impact on lateralization throughout the frequency spectrum.
Interaural Phase Difference
Coincident with the interaural time delay, varies systematically with source azimuth and wavelength due to distance from source and refraction around the head.
Isochronous
Time sensitive. Isochronous transmission is time sensitive transmission eg audio and video transmission for a television channel.
Knudson′s Law
The difference in frequency between pure tones of equal strength and of which the difference in pitch is just perceptible is defined by Knudson′s law.
LAeqT
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Ldn
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
LEDE
Abbreviation of Live End Dead End.
LEPN
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Live Room
Room characterized by a relatively small amount of sound absorption.
LN
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
LNP
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Localization Accuracy
Our ability to detect changes in localization or lateralization is not absolute.
Lombard Effect
As noise levels increase, talkers increase their voice levels to compensate and to maintain adequate conditions for verbal communication.
Loudness
A subjective term for the sensation of the magnitude of sound.
Low Frequency Sound
Acoustic waves below 20Hz are normally inaudible, but may be experienced as being in a region of high pressure.
LPK
Peak Sound Pressure Level
Macrosonics
The technology of sound at signal amplitudes so large that linear approximations are not valid.
Magneto-Optical Recording
Erasable optical disc system using magnetic media and laser reading/writing.
Masking
A property of the human auditory system by which an audio signal cannot be perceived in the presence of another audio signal.
Masking Threshold
A function in frequency and time below which an audio signal cannot be perceived by the human auditory system.
Mel
A proportional scale, in which equal intervals correspond to equal perceived interval sizes.
Middle Ear
The cavity between the eardrum and the cochlea housing the ossicles connecting the eardrum to the oval window of the cochlea.
Missing Fundamental
The phenomenon by which an observer, presented with a harmonic tone in which the fundamental is absent, hears the same pitch as would be heard if the fundamental had been present.
Moving Picture Experts Group
A working group within SMPTE who set, among other things, specifications for compression schemes for audio and video transmission.
Moving Pictures Experts Group
A working group within SMPTE who set, among other things, specifications for compression schemes for audio and video transmission.
MP3
More formally MPEG-1, layer 3. Audio compression format used for music streaming.
MPEG
Abbreviation of Moving Pictures Experts Group.
MPEG-1
Audio compression format used for music streaming.
MPEG-2
Image compression format for full motion video.
MPEG-4
Also known as structured audio is a standard based on describing the sound.
M/S Stereo
A method of removing imaging artefacts as well as exploiting stereo irrelevance or redundancy in stereophonic audio programmes based on coding the sum and difference signal instead of the left and right channels.
Muddy
A listening term, a sound that is poorly defined, sloppy or vague. For example, a "muddy" bass is often boomy with all the notes tending to run together.
Musical Twelfth
The third-harmonic of a tone, which equals one octave and a fifth. Hence, twelfth and not 13 because you don′t count the original tone.
NEF
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Noise Exposure Forecast
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Noise Exposure Limits
The amount of hearing loss is dependent on the noise level and duration.
Noise Pollution Level
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Noise Reduction Rating
Indicates a hearing protectors noise reduction capability.
NVH
Commonly used abbreviation for Noise, Vibration and Harshness
Objective Tinnitus
This refers to abnormal or pathological sounds originating within the body, in the region of the ear, which are audible to others than the subject.
Otologist
A physician who specializes in the ear and its diseases.
Overtone
A harmonic frequency related to the fundamental.
Passive Crossover
A loudspeaker crossover not requiring power for operation.
Peak Sound Pressure Level
ten times the common logarithm of the square of the ratio of the largest absolute value of the instantaneous sound pressure in a stated frequency band during a specified time interval to the reference sound pressure of 20 micro pascals.
Perceptual Coding
A lossy form of coding where parts of the signal that are not perceptible to the end user are removed.
Permanent Magnet Speaker
A speaker with a permanent magnet mounted on soft iron pole pieces.
Phantom Power
The standardized scheme of providing power supply voltage to certain microphones using the same two lines as the balanced audio path.
Pinna
The exterior part of the ear.
Pop
An undesirable short duration microphone output, often caused by explosive exhalation of air during the formation of certain vocal sounds.
Power Amplifier
An amplifier in which the output-signal power is greater than the input-signal power.
Precedence Effect
Delayed sounds are integrated by the auditory system if they arrive at the ear within 20 to 40 msec of the direct sound.
Presbycusis
Gradual and biologically normal loss of acute hearing with advancing age.
Privacy Index
A measure for rating the speech privacy performance of an architectural space.
Psychoacoustics
The study of the interaction of the auditory system and acoustics.
Pulse Code Modulation
Coding where the input signal is represented by a given number of fixed-width samples per second.
Pure Tone
A tone with a sinusoidal waveform.
Quarter Wave Tube
A resonator used most commonly on automotive air intake systems to reduce resonance.
Rapid Speech Transmission Index
Abbreviated as RASTI and expressed in a decimal range of 0.2 for "bad" to 1.00 for "Excellent".
Rasp
A sort of blowing noise emitted often from the exhaust pipes of internal combustion engines, usually, it is dominated by a mixture of 4E, 6E and 8E engine orders on 4 cylinder engines.
RASTI
Rapid Speech Transmission Index, expressed in a decimal range of 0.2 for "bad" to 1.00 for "Excellent".
Rayl
The Rayl is the SI derived unit of specific acoustic impedance.
Reactive Sound Field
A sound field in which the particle velocity is 90° out of phase with the pressure.
Reactivity Index
The reactivity index in a given direction at a point is defined as the difference between the sound intensity level and the sound pressure level measured in the given direction at that point.
Residual Intensity
This is the sound intensity level measured when the same signal is fed to both channels of a sound intensity measuring system, or it is exposed to a purely reactive sound field.
Room Acoustics
The general acoustic requirements of a room depend on the use.
SCART Connector
French-originated standard and associated 21-pin connector for connecting audio-visual equipment together.
SEL
There are a number of different noise criteria measurements used by local authorities to determine noise levels in the community.
Semitone
An interval equal to a half tone in the standard diatonic scale.
Sibilance
A hissing sound produced when pronouncing S and Z.
Significant Threshold Shift
A shift in hearing threshold, outside the range of audiometric testing variability.
Single Event Noise Exposure Level
The dB(A) level which, if it lasted for one second, would produce the same A-weighted sound energy as the actual event.
Sound Definition
This compares ‘useful’ sound with total sound.
Sound Focusing
Focusing of sound can be caused by reflection from large concave surfaces.
Sound Growth
The growth of sound in the room.
Sound Quality
Pertaining to the quality or other aspects of the machine that might be inferred from the sound it makes.
Sound Transmission Class
In acoustics, a single number rating for describing sound transmission loss of a wall or partition.
Sound Waves
Sound waves can be thought of like the waves in water.
Source
The object that produces the wave or disturbance.
Spectrum Analyser
An instrument for measuring, and usually recording, the spectrum of a signal.
Speech Coding
Excellent speech quality implies that coded speech is indistinguishable from the original and without perceptible noise.
Speed of Sound
Depends on the elastic and inertial properties of the particular medium.
Stereo
From the Greek meaning solid.
Stereo Irrelevance
A portion of a stereo audio signal which does not contribute to spatial perception.
Structured Audio
MPEG-4 is a structured audio format that describes sounds and transmits the description.
Subwoofer
A speaker designed exclusively for low-frequency reproduction.
Suppression
Elimination or reduction of any component of an emission, as a particular frequency or group of frequencies, in an audio or radio-frequency signal.
Tangential Mode
A room mode produced by reflections off four of the six surfaces of the room.
Tempo
The speed of occurrence of the beats for a given metric structure.
Threshold of Hearing
The equation defining the threshold of hearing.
Time History
A continuous record of the variation of a physical quantity (e.g. displacement, acceleration, force, etc.) with time.
Time Weighted Average
The yardstick used by the Occupational Safety and Health Administration to measure noise levels in the workplace.
Tinnitus
Persistent sensation of ringing noises in the ear.
Tinnitus Aurium
This refers a subjective sensation of noises in the ears.
Toe-In
Setting the front wheels to toe in will mean that when driven the wheels will tend to be aligned.
Treble
The higher frequencies of the audible spectrum.
Tuning Fork
A small two-pronged steel instrument which when struck produces a fixed tone.
Tweeter
A speaker that reproduces only frequencies above a certain range, usually about 3 kHz.
Universal Output Transformer
An audio output transformer having a number of taps on the secondary winding which provide a variety of impedances for matching the speaker impedance to that of the recommended load resistance.
Volume
There are a number of derived units of volume in the British system of units and the SI system of units.
Warmth
A term that is used to describe a listening term in terms of frequency, generally considered the range from approximately 150Hz-400Hz.
XLR Connector
A three pin connector widely used in the audio industry.
Z Weighting
Z-weighting is a flat frequency response of 10Hz to 20kHz ±1.5dB. This response replaces the older "Linear" or "Unweighted" responses as these did not define the frequency range over which the meter would be linear.

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