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

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

**LAn** : noise 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 LA10 and LA90, are extensively used for rating traffic noise and background noise respectively.

The measurement period should also be stated. For example, LA10 (18-hour) is considered good practice when reporting Road Traffic Noise measurements.

We also have a full page on background noise

**LAE** : SEL (sound exposure level) with "A" frequency weighting.

**LAF** :
A-weighted,
fast,
sound level.

**LAFmax** :
A-weighted,
fast,
maximum,
sound level.

**LAFmin** :
A-weighted,
fast,
minimum,
sound level.

**LAIeq** :
A-weighted,
impulse,
leq,
sound level.

**LAmax** :
A-weighted,
maximum,
sound level

**LArT : Sound Rating Level**, the a-weighted, leq sound level of an industrial noise during a specified time period, adjusted for tonal character and impulsiveness

**LAS** :
A-weighted,
slow,
sound level.

**LASmax** :
A-weighted,
slow,
maximum,
sound level.

**LASmin** :
A-weighted,
slow,
minimum,
sound level.

**Lavg** : averaged sound level with selectable exchange rate, results also vary depending if a threshold level was used.

**Lavg** : Leq - equivalent sound level measurements - but only when the exchange rate is 3 and the threshold is set to none.

**Lavg** : TWA - time weighted average when the exchange rates and threshold levels are the same and the measurement period was 8 hours.

**LC** :
C-weighted,
sound level.

**LCE** :
C-weighted,
sound exposure level

**LCeq** :
C-weighted,
Leq - equivalent sound level

**LCF** :
C-weighted,
fast,
sound level.

**LCFmax** :
C-weighted,
fast,
maximum,
sound level.

**LCpeak** :
C-weighted,
peak,
sound level.

**LCS** :
C-weighted,
slow,
sound level.

**LCSmax** :
C-weighted,
slow,
maximum,
sound level.

**LCSmin** :
C-weighted,
slow,
minimum,
sound level.

See also • community noise equivalent level • evening equivalent level

**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 worst 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

**LEPN** : Effective perceived noise level

**LEP,w** : Weekly personal noise exposure

**Leq** : Equivalent sound level

● 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 exposure level

**LF** : Force level

**LFNR** : Low frequency noise rating

**Lg or Log** : Logarithm

**Li** : Impact sound pressure level

**LIeq** : Impulse weighted average sound level, used in Germany, defined by DIN 45641 : 3 dB exchange rate.

**Linear**, a device or circuit with a linear characteristic means that a signal passing through it is not distorted.

See also other types of averaging

**Linear Momentum (p)** =
mass x velocity

● 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**, 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* should not be confused with the Peak.

Sometimes written as Min dB(A).

**Ln** : Logarithm

**Ln** : percentile level where 'n' is between 0.01 and 99.9% calculated by statistical analysis.

Usually include a descriptor i.e. A-weighting. Most common Ln values are LA10 and LA90 levels.

**Lnight : night equivalent level**,
Leq.
A-weighted,
sound level, measured overnight 23.00 - 0700 hours

Also known as the *night noise indicator* and other terms.

*LnT* : Standardized impact sound pressure level.

*L'nT* : Standardized impact sound pressure level.

*LnT,w* : Weighted standardized impact sound pressure level.

*L'nT,w* : Weighted standardized impact sound pressure level

**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

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 0 dB reference sound level - see the decibel for a more detailed explanation and practical examples in acoustics.

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 • frequency interval

● Note : modern precision instruments will be sampling at 16 times a second when calculating the logged results to ensure all the sound levels are included.

● Note : loudness depends primarily upon the sound pressure of the stimulus, but also upon its frequency, waveform and duration.

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

For measurements : see the B&K 2250 sound analyser

**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 in 2005. If you have current information we would be pleased to hear from you.

See also the comments in the frequency weighted sound levels section

**Low Pass Filter**, signals above the cut-off frequency are attenuated. The attenuation slope is called the roll-off

*Lpn* : Tone assessment parameter

*Lpt* : Tone assessment parameter

*Lpti* : Tone assessment parameter

L-weighting

**LZ** :
Z-weighted,
sound level.

**LZE** :
Z-weighted,
sound exposure level

**LZeq** :
Z-weighted,
Leq equivalent sound level.

**LZF** :
Z-weighted,
Fast,
sound level.

** LZFmax**.
Z-weighted,
Fast,
maximum,
sound level.

**LZFmin** :
Z-weighted,
Fast,
minimum,
sound level.

**LZS** :
Z-weighted,
Slow,
sound level.

**LZSmax** :
Z-weighted,
Slow,
maximum,
sound level.

**LZSmin** :
Z-weighted,
Slow,
minimum,
sound level.

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