1/3-Octave Band and Octave Band Spectrum (FFT)
This analyser derives the 1/3-octave band power spectrum and octave band power spectrum from a succession of fast Fourier transforms. Frequency bands are the IEC frequencies (with 1/3-oct bands based on round(10*log10(frequency)), and octave bands combining three adjacent 1/3-octave bands).
The advantages of deriving spectra in this way include:
- potential for short computation time
- small spectral leakage
The disadvantages of deriving spectra in this way include:
- low temporal resolution
- the underlying filtering process is not constant Q
- errors can occur from window steps that are too large
- the shorter the window length, the greater the error due to redistribution from linear to logarithmic frequency, especially in low frequency bands