1/12-Octave Band Spectrum (FFT)
This analyser derives the 1/12-octave band power spectrum from a succession of fast Fourier transforms. Frequency bands are the IEC frequencies (with 1/12-oct bands based on round(40*log10(frequency)). This is different to musical semitones in two ways: (i) the tuning frequency is not equivalent to A 440 Hz; and (ii) the semitones are slightly smaller for IEC frequencies.
The advantages of deriving 1/12-octave spectra from a simple redistribution of FFT output 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
