# Introduction

Leq encompasses a set of sound level meter specifications, which are described in detail in the BS EN 61672-1 European Standard.

Pure Analyzer implements the following Leq measurements: time-weighted sound level, time-average sound level and sound exposure level.

Frequency weighting is employed for all measurements, A being the standard and default, although other weightings can be specified if necessary.

The Leq module always measures the audio routed through the Mic channel.

## Time-weighted sound level

L_{A} is the root-mean-square sound level obtained after exponential time weighting.

Exponential averaging has the effect of progressively ‘forgetting’ past sample values.

The norm specifies two time-weighting constants:

The corresponding letter symbol is L_{AF} for an A-frequency weighted and F time-weighted sound level, for example.

## Time-average sound level

Time-average sound level is basically an RMS meter with frequency-weighting applied.

## Sound exposure level

This measures the sound exposure equivalent to a ‘dose’ received for a second.
It is useful for determining the amount of sound pressure to which listeners have been exposed for a certain duration.

This value naturally increases with time. For a constant source level, this value increases in a logarithmic fashion.