*Pac* ▷ sound power.

**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** 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

The following notations : dB SVL, dB(SVL), dBSVL or dBSVL are often seen but are not strictly correct

● 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

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**, a 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.

Peak Sound Level

Peak Sound Pressure

Peak Speech Power

Peak-to-Peak

● 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 • maximum perceived noise level • noise exposure forecast • noise and number index • tone-corrected perceived noise level

**Percentile Noise Levels (Ln)** the levels exceeded for n percent of the time, where 'n' is between 0.1 and 99.9% and 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.

**Personal Noise Exposure** see daily personal noise exposure and/or
weekly personal noise exposure.

Personal Sound Exposure Meter

**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

**Picket Fence Effect** information between samples in FFT spectrum analysis may be missing. hanning windows may help

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 • gaussian noise • narrowband noise • periodic • pseudo random noise • random noise • residual noise • specific noise • white noise • wideband noise

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 UK planning policy guidance is available for downloading

*PNL* ▷ perceived noise level

*PNLmax* ▷ maximum perceived noise level

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 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 • our full page on sound power and related parameters.

Power Reference Levels

*Power spectral density* is also known as *power spectrum density*.

**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

**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.

**Preferred Frequencies** a set of standardized octave and third-octave centre frequencies defined by BS EN ISO 266 : ISO 266

*Preferred frequency* is 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

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 Sound Intensity Index

Privacy Index

Progressive Waves

*Proportional*, two variables are proportional if there is always a constant ratio between them

*Directly proportional,* as one value increases, another value increases at the same rate.

*Inverse Proportional,* when one value decreases at the same rate that the other value increases.

Other noise descriptors • ambient noise • background noise • broadband noise • gaussian noise • narrowband noise • periodic • pink noise • random noise • residual noise • specific noise • white noise • wideband noise

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

**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

See also • complex sound • tone

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