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Basic audio terminology

TermDefinition
WaveA disturbance or oscillation that travels through space or a medium, transferring energy from one point to another without permanently displacing the particles of the medium.
Sound WaveA mechanical wave caused by vibrating objects, which propagates through a medium (like air) as alternating regions of compression and rarefaction.
Frequency ResponseThe quantitative measure of a system’s output magnitude and phase as a function of input frequency.
Magnitude ResponseAmplitude (loudness) component of the frequency response, typically represented in decibels (dB).
Phase ResponseThe component of the frequency response that expresses the timing or angular relationship between the input and output signal across frequencies.
On-Axis ResponseThe frequency response measured at a 0° angle of incidence from a sound source absent of reflections.
Off-Axis ResponseThe frequency response measured at angles other than at on-axis.
Listening WindowThe average of the frequency responses measured on-axis and at ±15° horizontally and vertically off-axis, excluding reflections.
Standing WaveA vibration pattern formed when two waves of the same frequency and amplitude travel in opposite directions and interfere, producing points of constructive and destructive interference that appear stationary in space.
Room ModeA specific frequency at which standing waves form in an enclosed space due to sound reflections between room boundaries, resulting in resonant peaks and nulls in the room’s frequency response.
Modal BehaviorRefers to how sound behaves in an enclosed space, typically at low frequencies, due to room modes.
Schroeder (Room Transition) FrequencyThe frequency below which room reflections dominate and modal behavior is significant.
Steady State MeasurementA frequency response measurement that includes both direct sound and all subsequent reflections in an environment.
Impulse Response WindowingA technique to isolate the direct sound in an environment’s impulse response by truncating later-arriving reflections, improving measurement accuracy at higher frequencies.
Head-Related-Transfer-Function (HRTF)A function that describes how an individual’s anatomical features (ears, head, torso) affect incoming sound, typically measured as the difference between a reference signal and what is received at the eardrum or ear canal.
Head-And-Torso-Simulator (HATS)A mannequin-based measurement device that simulates average human head and torso acoustics, often used for capturing HRTFs or binaural recordings.
Diffuse FieldAn acoustic environment where sound arrives equally from all directions, resulting in a uniform energy distribution. In headphone calibration, a diffuse-field target assumes a flat frequency response under such conditions when measured with a flat omnidirectional microphone.
Diffuse Field HRTFAn HRTF measured or modeled under diffuse-field conditions, representing how sound from all directions is filtered by the subject’s anatomy.
Transducer (Audio)A device that converts energy between electrical and acoustic domains, such as microphones (acoustic to electric) and loudspeakers (electric to acoustic).
Non-Linear DistortionDistortion products, such as harmonics or intermodulation, introduced by a transducer due to nonlinear behavior.
Dynamic CompressionA nonlinear effect where the output of a transducer increases less than proportionally with input level.
PolarityThe orientation of a waveform’s positive and negative voltage (or pressure) relative to a neutral centerline.
Absolute PolarityThe consistent directional behavior of an audio system in response to a positive input signal—e.g., whether a positive voltage pushes a speaker cone outward.