A measure of sound pressure level designed to reflect the response of the human ear, which does not respond equally to all frequencies, by reducing the effects of the low and high frequencies with respect to the mid-range frequencies. The resultant sound level is said to be A-weighted, and the units are dBA.

Analog representations of sound replicate its waveform, while transferring it through different media. All sound is analog, audio may be analog or digital.

To reduce the level (volume, loudness, energy) of an acoustical (or electrical) signal.

A frequency that falls within the range of the human hearing, usually taken as 20 Hz to 20 kHz

Listening term that usually refers to an excessive amount of low frequency (bass) energy.

Listening term that usually refers to excessive upper frequency (treble) energy.

The destructive interference of two or more sound waves. Waves of similar frequencies and amplitude, but of opposite phase (180°F) produce mutual cancellation effects.

A term used to indicate audible alterations to sound due to its environment. Coloration can be a result of standing waves or room resonances.

A distortion produced by combining an acoustical (or electrical) signal with a delayed replica of itself (offset in time). The result is constructive and destructive interference that results in peaks and nulls being introduced into the frequency response. This response, when plotted to a linear frequency scale, resembles a comb (teeth) rather than a smooth curve.

The addition of two waveforms of similar phase. Constructive interference is responsible for the production of standing waves in which a signal and its successive reflections are continually added to one another. The opposite is destructive interference.

A way for a musician to modify the musical instrument to affect the sound it produces. Musical instruments, including the voice, allow musicians to change pitch, loudness and even the tone color to some degree. For example, a trumpet can play the same note loud, brassy and bright, or softer with a mellow tone.

The lowest frequency above which the normal incidence sound absorption coefficient is at least .990 for an anechoic wedge, or set of wedges.

The frequency of an electrical signal or sound wave, measured in Hertz (Hz).

An acoustical condition in which reverberation is absent, as in a room whose surfaces are covered with highly absorptive materials.

The length of time taken for a signal to drop in strength to a specific portion of its initial value. Decay time is often frequency dependent. The decay time of a room at a specific frequency is the time necessary for a sound of that frequency to decay 60 dB. (RT60)

(dB) A unit of measurement commonly used to describe sounds around us. It’s based on a logarithmic scale which means a sound that is 3 decibels higher has twice as much energy.

Sound that is completely random in phase. Sound which appears to have no single source

The scattering or random distribution of a sound wave after striking a surface.

The apparent shift in frequency when the sound source, or the observer, is in motion.

A set of curves of equivalent loudness, which model the ear’s frequency response throughout the audible spectrum. The curves, obtained from actual testing, show how much more sound power is required at one frequency than another to obtain a sound of equal loudness. The results show that the human ear is less sensitive to sound at the extreme high and low frequencies.

The adjustment of timbre, or tone quality, achieved by changing the amplitude of a signal at different frequencies. (Abbreviated: EQ.) Tone controls are simple forms of equalization.

The term used to describe an even frequency response in which no frequency is accentuated.

The equal loudness contours plotted by the researchers Fletcher and Munson. Human ears are most sensitive to sound between 1,000 Hz and 4,000 Hz. Above and below those approximate frequencies, a tone must be several dB greater in order to be perceived as equally loud as a tone in the 1,000 Hz to 4,000 Hz range. See Weighting network.

The number of times a vibrating object oscillates (moves back and forth) in one second. Fast movements produce high frequency sound (high pitch/tone), but slow movements mean the frequency (pitch/tone) is low.

The basic pitch of a musical note.

Also called the precedence effect. Delayed sounds are integrated if they fall on the ear within 20 to 40 msec of the direct sound. The level of the delayed components contributes to the apparent level of the sound.

A measure of frequency, abbreviated as Hz. the number of oscillations (back and forth movements) per second.

The noise heard as a result of vibrations transferred through the structure of a room. Foot thumps are impact noise.

A very short, transient, acoustical (or electrical) signal.

Two periodic waves reaching peaks and going through zero at the same instant are said to be “in phase”.

The amount of sound energy radiated per unit area, measured in watts per square centimeter..

Any condition in which the magnitude of a physical quantity follows an inverse relationship to the square of the distance. 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.

Subjective impression of the intensity of a sound.

The process by which one sound is used to obscure the presence of another.

Common abbreviation for “monaural”, meaning from a single source.

The musical spacing between a frequency and its double. For example, the distance between “A” (440Hz) and “high A” (880Hz) is an octave. The audible range is about ten and one-half octaves.

A frequency spectrum which is one octave wide (i.e. all frequencies from 125 Hz to 250 Hz). In recording and audio testing, the octave itself is divided into thirds for increased accuracy.

Two related signals offset in time. See In Phase.

The length of time (measured in seconds) it takes for a wave to complete a cycle. t = 1/f

The time relationship between two signals.

The addition and/or subtraction of two waves of similar or multiple frequencies, causing peaks and dips in the overall response curve.

The time or angular difference between two signals.

The empirical unit of loudness. Since the ear has different sensitivities at various frequencies (Fletcher-Munson), it does not hear equivalent sound pressure levels as being equally loud.

Broadband noise whose energy content is inversely proportional to frequency.(-3dB per octave) This gives the noise equal energy per octave.

A measure for rating the speech privacy performance of an architectural space (or lack of speech intelligibility), where the PI is calculated from the Articulation Index (AI). A privacy level of PI above 95% represents confidential speech privacy whereas a PI of less than 80% is poor privacy.

How high or low a tone sounds to a person. High frequency sound has a high pitch or tone (treble notes), but low frequency has a low/deep pitch or tone (bass notes). High sounds are usually above 2000 Hertz and low below 200 Hertz.

The graphic representation of diffusion or scattering, over all incident angles at a rated frequency.

The positive (forward) or negative (backward) direction of an acoustical, electrical, or magnetic force. Two identical signals in opposite polarity are 180°F apart at all frequencies. Polarity, unlike phase, is not frequency dependent.

Sound arriving at the listening location after bouncing off one or more of the surrounding surfaces. The sum total of all reflected waves determine the room’s reverberation time and acoustical character.

The sympathetic vibration of an object (or air column) at a specific frequency when it is excited into motion by a sound wave of similar frequency in the immediate vicinity.

The degradation of transmission loss of a barrier at a specific frequency due to inner resonance. The exact frequency at which this phenomenon occurs is a function of the mass and stiffness of the barrier. Laminated “safety” glass has lower resonance, passing less sound than plain glass.

The persistence of sound in an enclosure after a sound source has been stopped. This is a result of the multiple reflections of sound waves throughout the room arriving at the ear so closely spaced that they are indistinguishable from one another and are heard as a gradual decay of sound. The area in which this occurs is the Reverberation Field.

The time, in seconds, required for sound pressure at a specific frequency to decay 60 dB after the source is stopped. 60 dB of decay is equal to one millionth of their original level. The reverberation time of a room varies with frequency and is a function of the room volume as well as the total number of absorption units in the room. It can be determined by the Sabine equation: RT60 = 0.049 V/a Where: RT60 = Reverberation Time V = volume of the space (feet cubed) a = sabins (total room absorption at given frequency)

Low-frequency vibration.

The difference between nominal or maximum operating level and the noise floor expressed in dB.

Having or producing a full, deep, or rich sound.

The intensity of sound measured with a sound level meter and one of its weighting networks.

The total sound energy radiated by a source per unit of time.

A mirror-like reflection. This is another instance where sound reflection properties are simplified by attributing to them the properties of light rays. A direct reflection from any surface incurring little or no attenuation. See Direct Sound

A device used to see the different waves (frequencies) that make up a sound.

A sound wave continuously reinforced by its own reflections, influencing the character of all sound within a room. Since the standing waves are a direct result of the size and geometry of the space itself, each room has a unique set of standing waves. The presence of these waves can easily be determined by a combination of mathematical calculation and audio analysis.

An integral sub-multiple of the fundamental frequency.

The minimum sound pressure level of a pure tone that can be perceived by a person with good hearing. A sound pressure of 20x10-6 Pascal (0.0002 mBar) is defined as 0dB SPL.

The minimum sound pressure level of a pure tone which causes a sensation of pain in the ear. (At approximately 140 dB SPL).

A descriptive rather than technical term usually applied to a well defined sound notable for its clarity and distinction. “Tight” usually refers to the absence of excessive reverberation and out of phase reflections.

The subjective tonal quality of a sound. The timbre of any musical or non-musical sound is determined largely by the harmonic structure of the sound wave. Rich sounding musical tones tend to have a great number of inner harmonics which contribute to their lush timbre, while thin sounding musical tones tend to be lacking in the presence of harmonics.

Refers to a sound notable for its prominence among other sounds.

A force which oscillates about some specified reference point. Vibration is commonly expressed in terms of frequency such as cycles per second (cps), Hertz (Hz), cycles per minute (cpm) or revolutions per minute (rpm) and strokes per minute (spm). This is the number of oscillations which occurs in that time period. The amplitude is the magnitude or distance of travel of the force.

A resilient support that tends to isolate a mechanical system from steady state excitation.

The cubic space capacity of a room bounded by walls, floors, and ceilings determined by the formula: Volume = Length x Width x Height. Volume influences reverberation time. Also: Colloquial for loudness.

The distance measured perpendicular to the wave front in the direction of propagation between two successive points in the wave, which are separated by one period. The distance between the beginning and end of a wave or cycle. Wavelength is determined by the formula: λ = C/f Where, λ (Lambda) = Wavelength in meters c = Speed of Light (299,792,458 m/s) f = Frequency Since wavelength and frequency are inversely proportional, low frequencies have much longer wavelengths than high frequencies. For example, a 1000 Hz signal would have a wavelength of approximately 13.5 inches, whereas a 40 Hz tone has a wavelength over 28 feet in length.

Broadband noise having a constant energy per unit of frequency. Random noise having uniform distribution of energy with frequency.