Three parallel frequency weighting networks (A/C/Z) are available. Most sound level
measurements are performed using the A-network (it corresponds to normal human hearing
ability at low or moderate sound levels) while peak levels often are detected using
the C-network. The Z-network is in fact flat, in other words, no weighting.
The frequency range can be divided into bands of octave or 1/3rd octave width. The
possible frequency range in the Nor145 is from 0.4 Hz to 20 kHz and thus
covers both the sound and vibration range.
The bandwidth decides the width of each filter. The bandwidth can be either 1/1 octave or 1/3 octave.
A lower limit can be set to the lowest frequency of interest. If the frequency is set lower than 6.3 Hz,
the
high-pass filter is disabled. The lowest selectable frequency is 0.4 Hz.
The upper frequency limit should be set to the highest frequency of interest. For the standard microphone,
the maximum frequency is 20 kHz. For other tranducers, the upper limit may be higher.