The settings allow to select the size of the transform, the choice of the apodization window, the overlapping between consecutive windows.
The output text file contains two colums: frequency and spectrum. Spectrum or Spectral density are calculated and can be expressed as amplitude, power or dB.
$ fft i test.txt o out.txt vvv n 512 O 2 t dbs Reading file test.txt ... Read 4096 entries. 14 FFT will be averaged. Input data sample rate: 10.00 Hz FFT SETTINGS: fft size 512 (frequency resolution 0.0195 Hz) Apodization window: Hann, Overlap 50% Effective Noise Bandwidth 0.0293 Hz FFT output: Spectrum in dB Aberrant Limit 1.80e+308. Saving data to out.txt Done.
Current version is 1.0.0.
fft binary and source can be downloaded through anonymous SVN at the following address:
https://anonsvn.loudet.org/fft/tags/
fftw
(http://www.fftw.org/) must be installed. For instance:
$ sudo aptget install fftw3 fftw3devThen, the classic installation steps are used:
./configure, make, make install
. Please read the INSTALL file from the package for details.
] [i, input= ] [o , output= ] [n {128,256,512,1024,2048,4096,8192,16384,32768,65536,131072, 262144,524288}, fft={...}] [w {none,rectangular,hann,hamming,gauss,blackman,nuttall,blackmanharris, blackmannuttall,flattop}, window={...}] [O {1,2,4,8,16}, overlap={...}] [t {ps,psd,ls,lsd,dbs,dbsd}, type={...}] [a , aberrant= ] Options: h, help display this help and exit. v[v...], verbose= increase/set verbosity level. i , input= Input filename. Defaults to stdin. File must contain two columns (x and y) of real data. o , output= Output filename. Defaults to stdout. Output file contains the following columns: n {128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288} fft={...} Set the size of the FFT. Default is 16384. w {none or rectangular,hann,hamming,gauss,blackman,nuttall,blackmanharris, blackmannuttall,flattop}, window= {...} Set the apodization window. Default is hann. O {1,2,4,8,16}, overlap={...} Set the samples overlap: 1 (0%), 2 (50%), 4 (75%), 8 (87.5%), 16 (93.75%) Default value is 2 (overlap = 50%). t {ps,psw,psd,psdw,ls,lsw,lsd}, type={...} Indicate the type of plot to calculate. ps Power Spectrum V^2 psd Power Spectral Density V^2/Hz ls Linear Spectrum V lsd Linear Spectral Density V/sqrtHz dbs Spectrum in dB dB [V] dbsd Spectral Density in dB dB [V/sqrtHz] Default is 'dbs' (spectrum in dB) a , aberrant= Threshold for aberrant values suppression. Difference between two consecutive data must not exceed the specified value. Aberrant values suppression is not enabled by default. EXAMPLE: fft i test.txt o out.txt n 2048 t dbs Generate a spectrum in dB (t) of data in file test.txt (c), store it in file out.txt, using a FFT width of 2048 (n). ]]>
SID monitoring station by Lionel LOUDET is licensed under a Creative Commons AttributionNonCommercialShareAlike 3.0 Unported License. 

Last Update: 16 Dec 2010 
Apache/2.4.54 (Debian) 