NTi Press Release

Objective Assessment of Tonal and Impulsive Noise

Perception of sound as melodic or just-a-noise depends on the listener; a lover of Mozart and Bach may feel that the heavy metal music at an Iron Maiden concert is noise. Conversely, very few die-hard rock fans would find themselves at a classical music concert. The passionate petrol-head is ok with a passing group of motorbikes; the local residents perhaps rather not. In short, what is noise and what is sound depends very much on the individual. The XL2 Sound Level Meter can measure for the objective assessment of noise according to the ISO 1996 standard.

Despite the varying perceptions of individuals, there is a general measure of noise and annoyance that assists in resolving disputes and limits; the Rating Level Lr. This essentially consists of the time-equivalent continuous sound level LAeq and adds penalties for prominent tones or impulses that could cause increased annoyance.

Tonal and Impulsive noise is perceived as disturbing
An example of a tonal sound is the sound of a circular saw. Particular tones stand out from the spectrum. If these are significantly louder than the background noise, the noise may be perceived as annoying. Accordingly, a tonal penalty KT is applied for periods during which such a noise source is active. Also, impulsive noises, such as from a piledriver on a construction site, or a hydraulic press in a factory, can be perceived as particularly annoying and are therefore adjusted with the impulse penalty KI.

First collect data, then create reports in peace
To determine the Rating Level Lr, the XL2 Sound Level Meter and the Data Explorer PC software are a perfectly-matched team. The XL2 stores all required level values as well as the 1/3rd-octave spectra in adjustable, short clock cycles. The XL2 also creates an audio file of the recorded noises. A keypad allows exceptional events to be marked during the ongoing measurement. These markers then appear in the graphs of the data in the Data Explorer. For remote, long-term unattended noise monitoring, the XL2 can be extended with the NetBox, and the level data viewed at any time through the NoiseScout website.

Automatic detection of Tonal or Impulsive sounds
The Data Explorer software graphically displays the level data and the 1/3rd-octave spectra; the audio file can be played in sync with the graph. This allows easy detection and marking of sounds that should be removed from the Rating Level calculation.
The software also automatically marks periods suspected of containing tonal or impulsive sounds. For the tonality, the KT penalty can be determined from the 1/3rd-octave spectrum or from the narrow-band FFT spectrum in accordance with the ISO 1996 standard. Based on this, Data Explorer calculates the Rating Level Lr. The limits vary from country to country.

Installation on any number of PCs
The Data Explorer software is the perfect tool for reworking the raw data captured by the XL2 Sound Level Meter to achieve the final Rating Level Lr. Data Explorer can be installed on any number of PCs. As an alternative to the permanent license, a low-cost annual subscription is also available. Software updates are free of charge for registered customers.
The recording of sound levels with impulse time-weighting and the storage of uncompressed wav files is made possible with the installation of the Extended Acoustic Pack Option on the XL2.

More about XL2 Sound Level Meter
More about Data Explorer
More about Environmental Noise Monitoring
Download the press pictures here