See also percentile noise levels.
LAeq,T is the 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. See also the daily noise exposure level • community noise equivalent level.
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
Lavg is the Leq (equivalent continuous 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.
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.
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.
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.
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.
LnT : standardized impact sound pressure level - insulation, laboratory measurements
L'nT : standardized impact sound pressure level - insulation, field measurements
LnT,w : weighted standardized impact sound pressure level - insulation, laboratory measurements
L'nT,w : weighted standardized impact sound pressure level - insulation, field measurements
Ln,w : weighted normalized impact sound pressure level - insulation, laboratory measurements
L'n,w : weighted normalized impact sound pressure level - insulation, field measurements
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 'handle'.
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 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
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 the comments in the A-weighted sound level entry
Lpti : tone assessment parameter.