**Parameter** an attribute with a value - for example, weighting.

On the other hand an object, like a cricket ball experiences acceleration, velocity and displacement literally so the general acceleration, displacement and velocity terms are more apt.

See also instantaneous particle acceleration

See also peak particle displacement

**Particle Velocity** the particles of a medium are displaced from their random motion in the presence of a sound wave. The velocity of a particle during this displacement is called the *particle velocity*, units m/s.

**Particle Velocity** is the speed of the particle and should not to be confused with the speed of sound.

**Particle Velocity** is related to the particle displacement and particle acceleration - as described above.

**Particle Velocity** multiplied by the sound pressure = sound intensity.

See also peak particle velocity

**Particle Velocity Level (Lv)** = 20 lg (v/vo) dB re 5 x 10^{-8} m/s and is also known as *Acoustic Velocity Level* and *Sound Velocity Level*

● Note 1 : unless otherwise specified, the reference velocity is 1 nm/s.

● Note 2 : unless otherwise specified, the velocities are understood to be expressed in root-mean-square values.

**Reference Particle Velocity Level : vo** = 5·10^{-8} m/s ≡ 0 dB

See also the IEC Definition of Level

**Pascal (Pa)** is the SI derived unit of pressure. It is a measure of force per unit area i.e. equivalent to one Newton per square metre or one Joule per cubic metre or 0.00001 Bar

1 Pa = 1 N/m^{2} = 1 J/m^{3} = 10^{-5} bar : kg·m^{-1}·s^{-2}

1 μPa = 1 micropascal = 10^{-6} Pa

Sound Pressure is measured in *Pascals*.

**Passband** the range of frequencies between filter cut-off frequencies defining the frequency band that is not attenuated.

Passive Sound Absorber

**Peak Detector** a peak detector responds in less than 100µs (microseconds), according to the sound level meter standards. A typical response time is 40µs.

Peak Frequency-weighted Sound Pressure Level

**Peak Hold** peak detection process retaining the 'true' maximum value of a signal.

See also particle displacement

If measurements are made in 3-axis then the resultant *PPV (peak particle velocity)* is the vector sum i.e. the square root of the summed squares of the maximum velocities, regardless of when in the time history those occur.

See also particle velocity • PPV measurements.

**Perceived Maximum Noise Level (PNLmax)** during aircraft flyover, see the **Effective Perceived Noise Level** definition below.

Peak Sound Level

Peak Sound Pressure

Peak Speech Power

Peak-to-Peak

**Perceived Noise Level (PNL)** jet engines are perceived to be noisier than propeller aircraft and led to the development in the 1960's of a scale based on equal loudness contours called Noys.

PNdB = 40 + 10 log2 (noy). As a rule of thumb, 100 dBA ~ 112 PNdB i.e. add 12 and an increase of 10 PNdb is equal to doubling it's Noy value.

See also the Noy

● Note 1 : the procedure is stated in ISO 3891-1978: Procedures for describing aircraft noise on the ground.

● Note 2 : Perceived noise level is intended to approximate judged perceived noise level.

See also effective perceived noise level • judged perceived noise level • tone-corrected perceived noise level

**Percentile Levels (Ln)** percentage exceeded levels where 'n' is between 0.1 and 99.9% calculated by statistical analysis - may also include other descriptors i.e. A, C, L or Z weightings. Most common Ln values are A-weighted L10 and L90 levels

**Period ( P)** a signal that repeats the same pattern over time is called **periodic** and the period is defined as the time it takes to complete one cycle, or repetition. The period of a periodic waveform is the inverse of its fundamental frequency = 1/f.

Permanent Threshold Shift (PTS)

**Personal Noise Exposure** see Daily Personal Noise Exposure and/or
Weekly Personal Noise Exposure.

Personal Sound Exposure Meter (PSEM)

**Phase** describes where in its cycle a periodic waveform is at any given time. the phase of a wave is given in
radians,
degrees, or fractions of a
wavelength.

**Phase Cancellation** occurs when two signals of the same frequency are out of phase with each other resulting in a net reduction in the overall level of the combined signal.

**Phase Difference** the relationship in time of two or more waveforms with the same or harmonically related periods gives us a measurement of their phase difference.

**Phase Function** is usually computed with coherence function, shows phase difference as a function of frequency between two sets of time series data.

This is the basis for the measurement of loudness in phons. If a given sound is perceived to be as loud as a 40 dB sound at 1000 Hz, then it is said to have a loudness of 40 phons.

See also Sones

PI Index under Sound Intensity Pressure Index

PI : Privacy Index

The piezoelectric property of materials is used in transducers that convert acceleration (or force) into electrical signals, and vice versa.

This is useful when using sound analysers with constant percentage bandwidth octave or third-octave filters, the net result is a flat spectrum

Other noise descriptors : ambient noise • background noise • broadband noise • narrowband noise • periodic • pink noise • pseudo random noise • random noise • specific noise • white noise • wideband noise

See also constant bandwidth • constant percentage bandwidths • octave bands • FFT - fast fourier transform.

They are single frequency devices, usually 250 Hz and include a calibrated barometer to correct for local changes in atmospheric pressure.

● Note 1 : the pitch of a complex wave depends primarily upon the frequency content of the stimulus, but it also depends upon the sound pressure and the waveform.

● Note 2 : the pitch of a sound may be described by the frequency of that pure tone having a specified sound pressure level that is judged by subjects to produce the same pitch.

Plane Wave or Planewave

**Planning and Noise** the Planning Policy Guidance PPG24 sets out the UK Government's policies on different aspects of planning. Local authorities must take their content into account in preparing their development plans.

Some planning policy guidance is available for downloading

PNC : Preferred Noise Criterion

PNL : Perceived Noise Level

PNLmax : Perceived Maximum Noise Level

PNR : Predicted Noise Level Reduction

We know from the inverse square law that the sound level pressure level decreases by 6 dB every time the distance between the measurement point and the source is doubled.

See also line source

**Polar Pattern or Response** microphones respond to sound coming from different directions with varying degrees of sensitivity. A plot or graph of this response is called a polar pattern (sometimes polar response curve). Similarly loudspeakers and other sound sources have Polar Responses.

Polar Patterns are frequency dependent, the low frequency response may be almost omnidirectional but the polar pattern will be come more directional as the frequency rises up the audio range.

Potential Sound Energy Density.

W = J/s joule per second = N m/s newton metre per second : base unit m^{2} kg s^{-3}

See also sound power and related parameters.

Power Reference Levels

**Power Spectrum Averaging** also called **RMS Averaging**, calculates the weighted average of the sum of the squared levels. The weighting is either linear or exponential. *Power Spectrum Averaging* reduces random fluctuations in the levels but does not reduce the noise floor.

See also other types of averaging

Power Spectrum Density Definition under Power Spectral Density Definition above

**Power Spectrum Level** the level of the power in a band one hertz wide referred to a given reference power.

**P-P** the amplitude difference between the most positive and most negative value in a time waveform, that is, the total amplitude.

PPG : Planning Policy Guidance 24

PPV : Peak Particle Velocity

**Preferred Frequencies** a set of standardized octave and third-octave centre frequencies defined by BS EN ISO 266 : ISO 266 - also known as Nominal Frequency.

Frequency | Octave | 1/3 octave | Frequency | Octave | 1/3 octave | Frequency | Octave | 1/3 octave | ||
---|---|---|---|---|---|---|---|---|---|---|

16 Hz | x | x | ||||||||

20 Hz | x | 200 Hz | x | 2000 Hz | x | x | ||||

25 Hz | x | 250 Hz | x | x | 2500 Hz | x | ||||

3.15 Hz | x | x | 315 Hz | x | 3150 Hz | x | ||||

40 Hz | x | 400 Hz | x | 4000 Hz | x | x | ||||

50 Hz | x | 500 Hz | x | x | 5000 Hz | x | ||||

63 Hz | x | x | 630 Hz | x | 6300 Hz | x | ||||

80 Hz | x | 800 Hz | x | 8000 Hz | x | x | ||||

100 Hz | x | 1000 Hz | x | x | 10000 Hz | x | ||||

125 Hz | x | x | 1250 Hz | x | 12500 Hz | x | ||||

160 Hz | x | 1600 Hz | x | 16000 Hz | x | x |

**Preferred Noise Criterion (PNC)** a noise measurement system for continuous or ambient noise in indoor environments proposed by Leo Beranek in 1971.

Preferred Speech Interference Level (PSIL)

**Pressure** is defined as the Force exerted per unit area. The SI unit of pressure is the Pa Pascal or N/m^{2} Newtons per square metre.

See also atmospheric pressure • static pressure • sound pressure and related parameters

Pressure Index

Pressure Intensity Index

The presence of the microphone should not to effect the measurement.

Because of their importance in acoustics we have a full page on Measurement Microphones

See also free-field microphones • random incidence microphones

Pressure Residual Intensity Index

Privacy Index (PI)

PRN : Pseudo Random Noise

**Probability Density** when analysing signals, the probability density is the probability that the signal level at some point in time lies within a defined area.

Progressive Waves

See also sound propagation

PSEM : Personal Sound Exposure Meter

PSIL : Preferred Speech Interference Level

**Psychoacoustics** the interaction of the human auditory system and acoustics.

PTS : Permanent Threshold Shift

**Pulse Code Modulation (PCM) and Adaptive Delta Pulse Code Modulation (ADPCM)** are subclasses of the WAV : waveform audio file format

**Pulse Code Modulation** works by taking discrete samples at even intervals (called the sampling rate). Common intervals are 11 kHz, 22 kHz, and 44 kHz. The higher the sampling rate, the better the representation of the original analogue wave and the better the sound quality.

**Adaptive Delta Pulse Code Modulation : ADPCM** is a form of compression, is a more efficient way of storing waveforms than 16-bit or 8-bit PCM

**Pure Tone** a tone with a single frequency, no harmonics, for example a sine wave.

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