Parameter : an attribute with a value - for example, weighting.
Partial : one of a group of frequencies, not necessarily
Harmonically related to the fundamental, which appear in a complex Tone. Bells and other percussion instruments have rich partials in their Spectra.
Particle : portion of a medium whose volume has dimensions which are small compared to the wavelength of the sound.
Particle Acceleration, Particle Displacement and Particle Velocity are terms used when discussing sound waves, where the particles 'assist' the transmission of the wave but then return to their 'original' state, no net movement.
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.
Particle Acceleration : a : to accelerate an air particle is to change its velocity over a period of time, the units are m/sec2.
Instantaneous Particle Acceleration : the time derivative of instantaneous particle velocity.
Particle Displacement : ξ : is a measurement of distance (in metres) of the movement of a particle in a medium as it transmits a wave. In most cases this is a Longitudinal Wave of pressure (such as sound), but it can also be a Transverse Wave, such as the vibration.
Displacement ξ = v/ω = a/ω2, where v =
Velocity, a =
Acceleration and ω = 2·π·f = angular frequency.
Instantaneous Particle Displacement : in an elastic medium, vector whose extremity is the position of the particle at a given instant, and whose origin is at the equilibrium position of the particle.
Peak Particle Displacement : greatest instantaneous particle displacement during a given time interval.
Particle Velocity : v : the particles of a medium are displaced from their random motion in the presence of a Sound Wave. The speed or velocity of a particle during this displacement is called the particle velocity, units m/s.
Instantaneous Particle Velocity : derivative, with respect to time, of the instantaneous particle displacement.
Peak Particle Velocity : PPV : greatest instantaneous particle velocity during a given time interval. If measurements are made in 3-axis then the resultant PPV is the vector sum = the square root of the summed squares of the maximum velocities, regardless of when in the time history those occur. Peak Particle Velocity instrumentation
Peak Particle Velocity : PPV : greatest instantaneous Particle Velocity during a given time interval. If measurements are made in 3-axis then the resultant PPV is the vector sum = the square root of the summed squares of the maximum velocities, regardless of when in the time history those occur.
Effective Perceived Noise Level : EPNL : a complex rating used to certify aircraft types for flyover noise, based on the Perceived Noise Level - PNL. Includes corrections for pure tones and for the duration of the noise.
The EPNL measurement is based on the following equation: EPNL = PNLmax + 10 lg (t/20) + F (dB)
where PNLmax is the maximum
Perceived Noise Level during flyover in PNdB, t is the duration in seconds during which the noise level was within 10 dB of the PNLmax and F is a correction for the
Pure Tone component, typically 3 dB.
Tone-corrected Perceived Noise Level : a Sound Pressure Level in decibels, obtained by adding to Perceived Noise Level an adjustment that is related to the degree of irregularity that may occur among contiguous one-third-octave band sound pressure levels of an aircraft noise.
Note 1 : the adjustment is described in ISO 3891-1978 ; it may vary from 0 dB to 6.7 dB.
Note 2 : the adjustment purports to account for the extra subjective noisiness caused by pronounced audible tones such as may be generated by propeller, compressors, turbines or fans.
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.
Phase : phase describes where in its cycle a periodic waveform is at any given time. the phase of a wave is given in
Degrees, or fractions of a
Phase Cancellation : 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.
Phase Lag : the delay between two tones of the same frequency measured in angular units of degrees or radians.
Phase Shift : the angular difference between two signals, which reflects the time difference.
Phase Velocity : velocity in the direction of propagation of a surface of constant phase.
Phon : two sounds may have the same sound intensity but may not sound equally loud because the human hearing sensitivity varies with frequency. Equal Loudness Contours which show the variation for the average human ear have been plotted. If 1000 Hz is chosen as the reference frequency, then each equal loudness curve can be referenced to the decibel level at 1000 Hz.
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.
Picofarad : pF : a million millionth of a Farad; 10-12farad
Picowatt : pW : a million millionth of a Watt; 10-12 farad
Piezoelectric : PE : any material which provides a conversion between mechanical and electrical energy. Piezo is a Greek term which means 'to squeeze'. If mechanical stresses are applied to a piezoelectric crystal then an electrical charge results. Conversely, when an electrical voltage is applied across a piezoelectric material, the material deforms.
The piezoelectric property of materials is used in transducers that convert acceleration (or force) into electrical signals, and vice versa.
Pink Noise : unlike White Noise which is uniform and characterless, the pink noise spectrum falls at 3 dB per Octave; so the energy content is inversely proportional to frequency i.e. -3 dB per octave or -10 dB per decade.
Pistonphone : microphone calibrator generating a known Sound Pressure Level, typically at a certain reference frequency. They are highly accurate, typically 0.1 dB and as the name suggests the sound level is generated by pistons moving air in a fixed coupler formed by the Pistonphone and the microphone under test.
They are single frequency devices, usually 250 Hz and include a calibrated barometer to correct for local changes in atmospheric pressure.
Pitch : is a subjective auditory sensation and depends on the frequency, the harmonic content, and to a lesser extent on the loudness of a sound.
Planning and Noise : Planning Policy Guidance : PPG24 notes set out the UK Government's policies on different aspects of planning. Local authorities must take their content into account in preparing their development plans.
Point Sound Source : source that radiates sound as if from a single point.
Point Source : a noise source whose dimensions are small compared to the propagation distances involved.
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.
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.
Post Processing : the application of a mathematical function to a signal after measurement to further improve the information that can be obtained from the analysis.
Power : P : is the rate at which Work is performed or Energy is transmitted. The unit of power is the Watt
W = J/s joule per second = N m/s newton metre per second : base unit m2 kg s-3
Power Spectral Density : PSD : the spectral density of the wave, when multiplied by an appropriate factor, will give the power carried by the wave, per unit frequency, known as the power spectral density (PSD) of the signal. PSD is commonly expressed in watts per Hertz (W/Hz)
Power Spectral Density Limit : as the bandwidth approaches zero, of Sound Power divided by Bandwidth.
Power Spectrum : the average squared magnitude of multiple frequency spectra.
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. RMS averaging reduces random fluctuations in the levels but does not reduce the noise floor.
Power Spectrum Level : the level of the Power in a band one hertz wide referred to a given reference power.
Predicted Noise Level Reduction : PNR : is the calculated noise level reduction at the ear when using ear protectors, based on the manufacturers' HML figures and the measured noise levels at the operators position.
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.
Preferred Noise Criterion : PNC : a noise measurement system for continuous or ambient noise in indoor environments proposed by Leo Beranek in 1971.
Presbycusis : impairment of hearing with age.
Pressure : Pressure is defined as the
Force exerted per unit area. The SI unit of pressure is the Pa Pascal or N/m2Newton per square metre.
Pressure Gradient : the change in pressure with distance, from lower to higher pressure, or vice versa. Used in the determination of Sound Intensity, the pressure gradient enables Particle Velocity to be measured.
Pressure Microphone : designed to measure the pressure that exists in front of the microphone diaphragm as opposed to the common Free-field Microphone. Used to measure the pressure in cavities or flush mounted in aircraft wings, etc.
The presence of the microphone should not to effect the measurement.
PCM 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.
ADPCM, is a form of compression, is a more efficient way of storing waveforms than 16-bit or 8-bit PCM
Pulse Rise Time : interval of time required for the leading edge of a pulse to rise from some specified small fraction to some specified larger fraction of the maximum value.
Pure Tone : a tone with a single frequency - no harmonics a Sine Wave. A sine wave is characterized by its Frequency - the number of cycles per second, or its Wavelength - the distance the waveform travels through its medium within a period, and the amplitude - the size of each cycle.