Abstract: The bandpass filter bank(BFB) is commonly used for octave analysis,which meets the national standard of octave-band and fractional-octave-band.And it is known that the number of filters and the amount of computation are greatly increased for fractional octave analysis.In this paper a multi-rate spectrum alogrithm is presented,and re-sampling and FFT theory are used to compute energy.A comparison is made between multi-rate spectrum method and BFB.It is shown by tests that the multi-rate spectrum algorithm has better resolution and less computation than the BFB method.