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/

- 1.0.0 (20101216): initial release

Under Linux, the library

`fftw`

(http://www.fftw.org/) must be installed. For instance:
$ sudo apt-get install fftw3 fftw3-devThen, 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,blackman-harris, blackman-nuttall,flat-top}, --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,blackman-harris, blackman-nuttall,flat-top}, --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 Attribution-NonCommercial-ShareAlike 3.0 Unported License. |

Last Update: 16 Dec 2010 |

Apache/2.4.59 (Debian) |

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