**LA** is the A-weighted, sound level.

**LA10** is the A-weighted, sound level just exceeded for *10%* of the measurement period, calculated by statistical analysis.

**LA10,18h (UK Traffic Noise Regulations)**, the arithmetic mean noise level in dB(A) exceeded for *10%* of each hour over the period 06:00 - 24:00 hours.

**LA90** is the A-weighted, sound level just exceeded for *90%* of the measurement period and calculated by statistical analysis.

**LAn** is the A-weighted, sound level exceeded for n% of the measurement period with
A-weighted, calculated by
statistical analysis - where n is between 0.01% and 99.99%.

The measurement period should also be stated. For example,

See also percentile noise levels.

**LAeq** is the A-weighted, equivalent sound level.

**LAeq,T** is the A-weighted, equivalent continuous sound level. T denotes the time period over which the fluctuating sound levels were avaeraged, for example *LAeq,8h* is the equivalent continuous noise level over an 8 hour period.

**LAeq,6h** (UK Government Environmental Noise Definition) is 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) is 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.

**LAeq,18h** (UK Government Environmental Noise Definition) is the equivalent continuous sound level in dB(A) that, over the period 06:00-24:00 hours, contains the same sound energy as the actual fluctuating sound that occurred in that period

See also Lday • Lden • Levening • Lnight.

**LAF** is the A-weighted, fast time-constant, sound level

**LAFmin** A-weighted, fast time constant, minimum, sound level

**LAS** is the A-weighted,
slow time constant response, sound level

**LASmax** is the A-weighted, slow response, maximum, sound level, *note : maximum is not peak*

**LASmin** is the A-weighted, slow response, minimum, sound level

**Lavg** is the average sound level, the results may vary due to local exchange rates and threshold levels.

**Lavg** is the Leq (equivalent sound level) when the exchange rate is 3 and no threshold is set.

**Lavg** is the TWA (time weighted average) measured over 8 hours. In Europe and the UK a 3dB exchange rate is always used.

**LC** is the C-weighted, sound level

**LCE** is the
C-weighted,
sound exposure level

**LCeq** is the
C-weighted,
Leq (equivalent sound level)

**LCF** is the
C-weighted,
fast response,
sound level

**LCFmax** is the
C-weighted,
fast response,
maximum,
sound level, *note : maximum is not* peak

**LCS** is the
C-weighted,
slow response,
sound level

**LCSmax** is the
C-weighted,
slow response,
maximum,
sound level

**LCSmin** is the
C-weighted,
slow response,
minimum,
sound level

See also Lden • Levening • Lnight

See also community noise equivalent level • Lday • Levening • Lnight

**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.

● 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.

See also sound insulation level difference

**Li** is the impact sound pressure level

**Li** is the sound intensity level

See also other types of averaging

See also elementary attenuation of propagation • elementary dephasing of sound propagation • elementary exponent of sound propagation • propagation loss definition

● 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.

Linear Weighting

See also inverse square law

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* should not be confused with Peak.

**Ln** is the normalized impact sound pressure levels - sound insulation, laboratory measurements.

**L'n** is the normalized impact sound pressure levels - sound insulation, field measurements

See also Lday • Lden • Levening

**LnT** is the standardized impact sound pressure level - insulation, laboratory measurements

**L'nT** is the standardized impact sound pressure level - insulation, field measurements

**LnT,w** is the
weighted standardized impact sound pressure level - insulation, laboratory measurements

**L'nT,w** is the
weighted standardized impact sound pressure level - insulation, field measurements

**Ln,w** is the weighted normalized impact sound pressure level - insulation, laboratory measurements

**L'n,w** is the weighted normalized impact sound pressure level - insulation, field measurements

See also binaural and our HATS - head and torso sumulator

Presentation of data on a logarithmic scale can be helpful when the data covers a very large range of values - the logarithm reduces this to a more manageable range. For example 120 dB is 'equivalent' to 1,000,000 relative to a reference sound level of 0 dB - see our decibel calculation and examples page.

The *common logarithm* is the logarithm to the base 10 and is often written as log10(x) or log (x) but this can be ambiguous or confusing as log on a calculator often refers to natural logarithms, favoured by mathematicians, with a base of e (~2.718).

The *binary logarithms* to the base 2 is used in computer science.

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).

See also the IEC Definition of the Decibel and our sound level calculations and examples page

But a logarithmic scale shows prominent vibration components equally well at any amplitude. Moreover, percent change in amplitude may be read directly as dB change. Therefore, noise and vibration frequency analyses are usually plotted on a logarithmic amplitude scale.

See also • frequency interval

● Note : modern precision instruments sample at 16 times a second to ensure all the sound levels are included.

Longitudinal Wave

**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.

See also • calculated loudness level • equal loudness contours • fletcher munson curves • methods for calculating loudness • minimum audible field

See also the comments in the A-weighted sound level entry

**Lpt** is the tone assessment parameter

**Lpti** is the tone assessment parameter

**LZ** is the Z-weighted, sound level

**LZE** is the Z-weighted, sound exposure level

**LZeq** is the
Z-weighted,
Leq equivalent sound level

**LZF** is the
Z-weighted,
fast response,
sound level

**LZFmax** is the
Z-weighted,
fast response,
maximum,
sound level

**LZFmin** is the
Z-weighted,
fast response,
minimum,
sound level

**LZS** is the
Z-weighted,
slow response,
sound level

**LZSmax** is the
Z-weighted,
slow response,
maximum,
sound level

**LZSmin** is the
Z-weighted,
slow response,
minimum,
sound level

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