Cirrus Research, a company specialising in the design and development of acoustic measurement instruments, is innovating with a new sound source recognition module for the Optimus Environmental Sound Level Meters. Based on the audio recording of noise, the aim of this module is to trigger recordings when a specific noise has been recognised. This innovation was presented at Internoise 2010 by engineers from Cirrus Research plc.
Audio recording
The audio recorder function allows Optimus Environmental sound level meters to be used as a sound sample recorder that can be played back using NoiseTools software. Audio recordings are stored as WAV format files and can be Standard Quality (16bit, 16kHz, WAV) or Studio Quality (32bit, 96kHz, WAV).
Detection based on threshold exceedance
Threshold overshoot is the simplest instruction, based on a single value that triggers recording when it is exceeded.
Smoothing coefficient
Triggering can use a smoothing coefficient to reduce the effect of peaks before trigger instructions are applied. This can be very useful for reducing the number of false recordings.
Detection based on Change Ratio
Identifying noise sources through ‘subjective listening’ can be a powerful tool for interpreting environmental noise measurements. For example, the noise of people outside a discotheque and birdsong cannot be distinguished using the LAeq,1s graph. Listening to a sound sample taken at the time when the noise is annoying will help considerably in distinguishing between different noise sources.
Instructions based on the ‘Ratio of change’ are more advanced than those based on a simple threshold. They use the ratio of change in the sound level to determine the trigger conditions. This opens up the possibility of detailed and very sophisticated parameterisation aimed at distinguishing noise sources in terms of frequency, level and change ratio without taking residual background noise into account.
As with all Cirrus instruments, the Optimus Environmental sound level meters are covered by an initial 12 month warranty, which can be extended by a further 14 years when the equipment is maintained and recalibrated annually by a Cirrus service centre. The software is freely licensed and users have access to updates from our website.
