See also percentile noise levels.
LAeq,T : A-weighted equivalent continuous sound level, T denotes the time period over which the fluctuating sound levels were averaged, for example LAeq,8h is the equivalent continuous noise level over an 8 hour period.
LAeq,6h (UK Government Environmental Noise Definition) : the equivalent continuous sound level in dB(A) that, over the period 24:00-06:00 hours, contains the same sound energy as the actual fluctuating sound that occurred in that period.
LAeq,16h (UK Government Environmental Noise Definition) : the equivalent continuous sound level in dB(A) that, over the period 07:00-23:00 hours, contains the same sound energy as the actual fluctuating sound that occurred in that period.
Lavg : Leq (equivalent continuous sound level) when the exchange rate is 3 and no threshold is set.
Lavg : TWA (time-weighted average), measured over 8 hours. In Europe and the UK a 3dB exchange rate is always used.
Lden : day-evening-night noise level, the A-weighted, Leq (equivalent noise level) over a whole day, but with a penalty of 10 dB(A) for night-time noise (23:00-07:00) and 5 dB(A) for evening noise (19:00-23:00), also known as the day evening night noise indicator
Ldn : day-night noise level, the LAeq (equivalent noise level) over a 24 hour period with a penalty of 10 dB(A) for noise during the hours of 23:00-07:00, also known as the day night indicator.
Leakage in an FFT analyser, the input signal is recorded in time blocks, called time records, and individual spectra are computed from each block of data. Because the input signal period is not synchronised with the duration of the time block, the signal will be truncated at the beginning and end of the block. This truncation causes an error in the calculation, which effectively spreads out, or 'smears', the spectrum in the frequency domain
This phenomenon is called leakage or spectral leakage it reduces the accuracy of the measured levels of peaks in the spectrum, and reduces the effective frequency resolution of the analysis.Leakage is worse for continuous signals and rectangular window, and it is greatly reduced by use of the hanning window, a form of apodization, which forces the signal level to zero at the ends of the data block.
LEP,d : daily personal noise exposure level.
Level Definition (IEC 801-22-01) logarithm of the ratio of a given quantity to a reference quantity of the same kind. The base of the logarithm, the reference quantity, and the kind of level must be indicated.
Note 1 : the kind of level is indicated by use of a compound term such as sound power level or sound pressure level.
Note 2 : the value of the reference quantity remains unchanged, whether the chosen quantity is Peak, RMS, or otherwise.
Note 3 : the base of the logarithm is indicated by use of a unit of level associated with that base.
LEX,8h : daily noise exposure level
LFNRV : low frequency noise rating
Lg : logarithm
Linear, a device or circuit with a linear characteristic means that a signal passing through it is not distorted.
Linear Averaging, the process of adding together a sequence of spectra measurements and then dividing the total by the number of samples. The result is a true arithmetic average on a sample by sample basis. Averaging smooths out random noise components in a spectrum.
See also other types of averaging
Linear Exponent of Sound Propagation Definition (IEC 801-23-33) with respect to a uniform system, natural logarithm of the complex ratio of particle velocities (or pressures) measured at two successive points separated by unit distance, when this system is assumed to be of infinite length, also known as the sound propagation coefficient
Linear System Definition (IEC 351-42-11) system the behaviour of which obeys the principle of superposition.
Note 1 : the principle of superposition implies that such a system may be described by a set of linear equations.
Note 2 : a system, which does not have this property, is called nonlinear system.
Line Drive, an input socket that can also provide power to drive a transducer.
Line Source, a sound source composed of many point sources in a defined line, such as a train, flow of traffic on a motorway, or constant aircraft take-offs and landings. Sound levels measured from line sources decrease at a rate of 3 dB per doubling of distance.
See also inverse square law
Line Spacing is the frequency difference between two adjacent 'lines' in a line spectrum
See also constant bandwidth • constant percentage bandwidths • continuous spectrum • fast fourier transform • narrowband noise • narrowband spectra • octave bands. pink noise • white noise • wideband noise.
Lmax, the maximum sound level, during a measurement period or a noise event, Often includes other descriptors, for example LAFmax, and sometimes written as Max dB(A).
Lmax should not be confused with Peak.
Lmin, the minimum sound level, during a measurement period or a noise event. Often includes other descriptors, for example LAFmin, and sometimes written as Min dB(A).
Ln is the percentile noise level where 'n' is between 0.01 and 99.9%, of the time, calculated by statistical analysis and usually includes a descriptor i.e. A-weighting. The most common Ln values are the LA10, LA90 and LA95 levels, widely used in the assessment of environmental noise levels and regulations.
Ln is also used in sound insulation assessments
Ln : normalised impact sound pressure levels - sound insulation, laboratory measurements.
L'n : normalised impact sound pressure levels - sound insulation, field measurements
Lnp : noise pollution level
LnT : standardised impact sound pressure level - insulation, laboratory measurements
LnT,w : weighted standardised impact sound pressure level - insulation, laboratory measurements
L'nT,w : weighted standardised impact sound pressure level - insulation, field measurements
Ln,w : weighted normalised impact sound pressure level - insulation, laboratory measurements
L'n,w : weighted normalised impact sound pressure level - insulation, field measurements
Localisation, the listener's ability to respond to time and level differences between both ears as well as spectrum information, correlation and pattern matching
See also binaural and our HATS - head and torso sumulator
Logarithm, Log, log, lg, Ln, (common logarithm ratios), expressed in decibels (dB) are widely used in acoustics to convert the immense range we can hear into manageable numbers.
For example we can hear sound power levels of 0.000000000001 watts up to 100 watts or more.
Similarly we can hear sound pressure levels of 0.00002 pascals up to 200 pascals.
Converting these levels into dBs results in a range of values 0 dB up 140 dB; much easier to compare and discuss.
The Binary logarithm (log2n) is used in computer science.
The Common logarithm is the logarithm to the base 10 and is often written as log10(x) or log (x) but this can be confusing as the "log" on most calculators refers to natural logarithms, favoured by mathematicians, with a base of e (~2.718).
The Natural Logarithm is the logarithm to the base of the mathematical constant e, where e is approximately equal to 2.718281828459. The natural logarithm of x is generally written as ln x, loge x,
To overcome this possible confusion, ISO, the International Standards Organisation, recommend:-
log10(x) should be written lg (x) and
loge(x) should be written ln (x).
Logarithmic Amplitude Scale, critical vibration components usually occur at low amplitudes compared to the rotational frequency vibration. These components are not revealed on a linear amplitude scale because low amplitudes are compressed at the bottom of the scale.
But a logarithmic scale shows prominent vibration components equally well at any amplitude. Moreover, percent change in amplitude may be read directly as a dB change. Therefore, noise and vibration frequency analyses are usually plotted on a logarithmic amplitude scale.
See also frequency interval
Logging is the process of recording the noise data at regular intervals, so a 'picture' of the fluctuations may be studied at the end of a measurement. Traditionally results are logged at 1 second or 1 minute intervals but it can be as much as 1 hour in some cases.Note : modern precision instruments sample at 16 times a second to ensure all the sound levels are included.
Loudness depends not only on the sound levels and the frequencies involved, but also on the individual listener's subjective response to the character of the noise under consideration.
Loudness Definition (IEC 801-29-03) that attribute of auditory sensation in terms of which sounds may be ordered on a scale extending from soft to loud.
Note : loudness depends primarily upon the sound pressure of the stimulus, but also upon its frequency, waveform and duration.
Loudness Level Definition (IEC 801-29-05) of a sound, in phons, numerically equal to the median sound pressure level in decibels, re 20 μPa of a free progressive wave having a frequency of 1,000 Hz presented to listeners having normal hearing facing the source that in a specified number of trials is judged equally as loud as the unknown sound.
Low Frequency Noise Rating (LFNR), we have no experience in this specific rating and just include it for completeness. We are aware of the 'proposed criteria' produced for DEFRA by the University of Salford .
See also the comments in the A-weighted sound level entry
Low Pass Filter, signals above the cut-off frequency are attenuated. The attenuation slope is called the roll-off
Lp : sound pressure level.
LPac : the sound power.
Lpeak and Lpk : peak sound pressure
Lpti : a tone assessment parameter.