Leq Metering

Introduction

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

FLUX:: MiRA 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.

Leq slots

A Leq slot is an independent measurement buffer used by one or more Leq scopes. The slot stores the running state of the measurement: selected mic input, weighting, measurement type, integration time, current value, maximum value, and log identity. Several Leq scopes can display the same slot, or each scope can use a different slot.

Use different slots when you need parallel measurements from the same layout, for example:

Fast and Slow dBA on the same microphone.
10-second Leq and sound exposure level during the same event.
A front-of-house microphone and a stage microphone displayed side by side.

Use the same slot when you want the same Leq measurement visible in several layouts or views without restarting its history.

Tip

Name each slot by its purpose, such as FOH 10s, Audience Slow, or Stage SEL. Clear names make log files and screenshots easier to interpret later.

Important

Changing the slot changes which measurement buffer the scope displays. Reset the slot before a new measurement pass if the previous values should not be included in the next reading or log.

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:

Fast: 125ms
Slow: 1s

Note

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.

Note

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.

Logs and log files

Each Leq meter features two special buttons to create log files. Log files are simple markdown files that register the state of the metering every three seconds. The path of storage of this file is defined in the option of the Leq scope (see below).

Important

All the different Leq scopes in the same layout share the same settings for log files. Specifically, they all write their data to the same output file.

Starting a log file

A log file is created as soon as the “play” button over the scope is pressed. The file is created at the location specified in the scope options.

It is named as follows: analyzer_metering_log_YYYYMMDDHHMM, where, in order, Y is Year, M is Month, D is day, H is Hour and M is Minute. For example: analyzer_metering_log_202408291015 is a log file created on the 29th of August 2024 at 10:15 AM.

Custom notes

At any point, you can click on the “pencil” button over the scope to enter a specific note in the log file. Like all other data entries, it will be timestamped with the application’s current time code.

Log file content

The log file shows the following data as a table:

The Timecode
The maximum true peak level
The true peak level per channel
The RMS level per channel
The different Leq scopes of the layout.
the loudness

Each row of the table corresponds to a specific timecode.

Next, you will find some global data:

The maximum true peak level
The maximum true peak level per channel
The maximum RMS per channel
The maximum value for each Leq scope
The maximum loudness

Settings

General

Name	Description
Scope name	The name of the scope, indicated in the scope header.
LEQ slot	The LEQ slot used.
Name	The name of the meter.

IO

Name	Description
Mic input	The mic input of the LEQ.
Weighting	Frequency weighting employed for metering. Can be switched between ANSI standards (A, B, C, D) and none. The default is A.
Measure type	The type of measurement to be performed. Can be switched between Leq, Equivalent continuous sound level, and Sound exposure level.
Integration type	Indicates the time constant for the metering.
Time unit	Time unit of the Integration type

SPL

Name	Description
SPL reference	This is the reference level of the calibrator’s output, indicated on the device itself or in the corresponding data sheet. A typical value is -94dB.
SPL trim	This is the offset applied to RMS dB values in order to obtain dB SPL readings. It is determined automatically by the calibration procedure.
Calibrate	Press this button after having inserted the microphone into the calibrator socket and activated it in order to determine the SPL trim value.

Logs

Name	Description
Log time in seconds	Set the lapse of time between two log entries
Set logging path	Set where the log files are stored.

Color

The following settings control the visual aspect of the Leq display.

Name	Description
Level	Level display color
Name	Name font color
Unit	Unit display font color.
Freq. weighting	Frequency weighting type display font color.