Computing acoustic spectrum

bearcat

Does anyone know any good method to compute the acoustic spectrum accurately? I am doing an aeroacoustic simulation and need to convert a pressure variation signal into acoustic spectrum and compare it with experimental result from others.

I hear that we can do this by doing a Fourier transform or analog filtering. So at first, I tried the FFT in Matlab. It worked well predicting the low frequency but under-estimate the dominant peaks. I also tried some PSD functions and converted them back into dB-Hz spectrum. They generally over-estimated the magnitude. Finally I tried the FFT post-process program in Fluent. It can accurately capture one peak in frequency and SPL, but leaving other range over-estimated. So does any one know any accurate method or software to compute this?

What I have now are about 35000 signal points from steady oscillation stage. I think they are enough for doing a time series analysis.

Thanks,

Bearcat