Fractional octave filtering

Fractional octave filtering allows filtering in the time and frequency domain using octave band or fractional octave band filters according to DIN EN 61260.

Bandwidth [1/oct] defines the band width of the filters in fractions of octaves.

Lower band [Hz] sets the center frequency of the lowest filter.

Upper band [Hz] sets the center frequency of the highest filter.

Reference [Hz] sets the reference center frequency. Based on this frequency all the center frequencies are determined, using the value chosen for Basis. With a Basis of 2 the center frequencies of the octave filters are separated exactly by the factor 2, with a Basis of 10 by the factor 10^(3/10)≈1.99526.

Class 1 tol. and Class 2 tol. create tolerance curves according to the norm, illustrating the different degrees of tolerance.

If Create band level spectrum is activated, for each output curve a spectrum is created with the levels of the filtered bands.

The channel is chosen by Select channel.

After the filtering for each filter band there is a channel in the time domain.

As an example of an application the following plot shows motor noise recorded at 4 microphone positions.

After the octave band filtering, for each of the 4 channels the time signal is displayed in octaves, resulting in a total of 32 channels:

Using the Info window, statistical values of the filtered channels, such as crest factor or Leq, can be evaluated in detail.

If Create band level spectrum is activated, additionally the corresponding spectrum of band levels is created in the frequency domain: