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Frequency Axis Scaling
There are two basic types of frequency axis scaling: Narrowband and Octave. Narrowband scaling can be displayed in either Linear or Logarithmic format; Octave scaling is always displayed in Logarithmic format.
Narrowband Scaling
The spectrum produced by an FFT algorithm is also known as a narrowband spectrum. Each spectral line is a constant bandwidth and typically quite narrow. This narrowband spectral data can be displayed on either a linear or logarithmic scale but the frequency resolution is determined by the sampling rate and FFT size and remains unchanged as you increase in frequency.
The resolution of each spectral line is equal to:
Resolution = Sampling Rate / FFT size
Octave Scaling
Octave scaling produces a set of bands with constant proportional bandwidth. You can select from a range of octave formats. 1/1 and 1/3 octave are the most commonly used formats. See the Octave Scaling topic for more details.
See Also: Amplitude Axis Scaling, Scaling