In order to resolve the low resolution in low frequency for
converting from FFT (fast Fourier transform) spectrum to onethird
octave spectrum, two FFT analyzers in parallel should be
used. One analyzer is set at 400 Hz with frequency resolution at
0.5 Hz and the other one is set at 1600 Hz with frequency
resolution at 2 Hz. After the conversion of both the spectra, the
two converted spectra are combined into a complete one-third
octave spectrum from 0 to 1250 Hz.