The measurement period should also be stated. For example,

See also • percentile noise levels.

See also • community noise equivalent level

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 the kind of level is indicated by use of a compound term such as sound power level or sound pressure level.

● Note 2 : the 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 • Lday • Lden (day-evening-night) • Lnight.

**Lg or Log** under logarithm

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* see also •
logarithm •
normalized impact sound pressure level

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

● 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 modern loudness measurements, see the B&K 2250 sound analyser

See also the comments in the frequency weighted sound levels section

L-weighting

**LZ • **
Z-weighted,
sound level

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

**LZeq •**
Z-weighted,
Leq equivalent sound level

**LZF •**
Z-weighted,
fast response,
sound level

**LZFmax •**
Z-weighted,
fast response,
maximum,
sound level

**LZFmin •**
Z-weighted,
fast response,
minimum,
sound level

**LZS •**
Z-weighted,
slow response,
sound level

**LZSmax •**
Z-weighted,
slow response,
maximum,
sound level

**LZSmin •**
Z-weighted,
slow response,
minimum,
sound level