Octave band analysis is a method of analyzing the frequency content of a signal by dividing the frequency range into bands that are proportional in width. In a standard full-octave plot, each band spans a frequency range that is twice the width of the previous one and half the width of the next. This type of analysis is particularly suited for acoustic and audio measurements, as it aligns with how the human ear naturally perceives sound.


By grouping frequencies into octave bands, it's easier to compare sound energy levels across a broad range, offering meaningful insights into the subjective quality of sound - such as loudness or tonal balance.


Fractional Octave Plots


To achieve greater frequency resolution, octave bands can be subdivided into smaller intervals:


  • 1/3 Octave
  • 1/6 Octave
  • 1/9 Octave
  • 1/12 Octave


These options are available in SIGVIEW as separate functions and follow the same principle as standard octave analysis but offer finer frequency granularity, making them ideal for detailed sound measurement and analysis.


All octave plot functions can be accessed via the “Signal Tools” menu:



Implementation


In SIGVIEW, octave analysis is implemented using a Custom Filter bank plot, rather than FFT-based methods. This approach ensures compliance with established acoustic measurement standards, such as ISO 266, which define the behavior and structure of octave bands.


Each octave type uses a corresponding filter bank definition file located in the "filters" subdirectory of the SIGVIEW application data directory. The files are named "octave filter.flb",  "1_3_octave_filter.flb", "1_6_octave_filter.flb" etc.

These files contain the frequency definitions for each filter bank and can be freely edited using a text editor to customize the analysis to your specific needs. For details on how to modify filter banks, refer to the custom filter bank chapter.


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