Octave and one-third octave band representations of measurements are widely used in sound level meters. While spectrums for audio applications are rather typically represented by high-resolution FFTs, there are also audio applications where octave or one-third octave band results are preferred or even required by the standard. From firmware V2.9.0, the FX100 Audio Analyzer supports fast and direct measurement of both FFT and octave and one-third octave band spectrums.
How does it work?
Conventional sound level meters with spectral analysis continuously feed the microphone signal through band-pass filters. (Real-Time Analyzer, RTA) Each octave or one-third octave band has its own, permanently active filter.
By contrast, the FX100 Audio Analyzer reads the measured signal over a precisely defined period of time and transforms it into the frequency domain by means of an FFT.
For calculation of octave and one-third octave band levels from FFT results, the FFT signal is filtered and summed up. The filters meet the requirements of Class 0 according to the IEC61260 standard.
Consistent Signal Required
To calculate octave and one-third octave spectra from a time-limited FFT measurement, important conditions must be met: the measured signal must produce a constant spectrum and should show no large dynamic level changes. Pink noise is a commonly-used test signal. Also suitable are the sounds emitting from appliances or machines (e.g. electric or internal combustion engines).
Octave and one-third octave band measurements in FX Control
The FX100 Audio Analyzer with the FX-Control PC software provides an integrated measurement function supporting octave and one-third octave band analysis. In addition to faster analysis, the new solution is more comfortable to operate. The measurement data is immediately available for display, calculation and storage.