To determine the frequency components of a sound, “octave band analysis”, in which frequencies are segmented into proportionate widths (octave bands), is used. In a standard full-octave plot, each band occupies a bandwidth that is twice as wide as the previous band and half as wide as the next band.


Octave analysis corresponds to the way how people perceive sounds because it allows you to compare signal levels across broad frequency ranges. Breaking frequencies into octaves helps you measure the subjective qualities of sound.


To achieve a better frequency resolution, each octave band can be divided into 3 bands. This is called a “1/3 octave plot” and is available as a separate function in SIGVIEW.


Both octave and 1/3 octave plot functions can be found in the "Signal tools" menu.


Implementation


Both Octave plot functions are implemented by using the Custom Filter bank plot function and not by using FFT. This is required by the various technical standards defining octave plot calculations.

 

Filter bank definition files can be found in the "filters" subdirectory of the SIGVIEW application data directory. The files are named "octave filter.flb" and "1_3_octave_filter.flb". As for all custom filter bank plots, you can freely change the frequency values in these files by using any text editor. For details, see the custom filter bank chapter.


By default, octave plots are displayed by using a histogram display type (min-reference). As for all other plots, you can change the display type by using a context menu or toolbar buttons (Display type option).


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