de.gsi.math.spectra

Class ShortTimeFourierTransform

java.lang.Object

de.gsi.math.spectra.ShortTimeFourierTransform

public class ShortTimeFourierTransform
extends Object

Static utility class providing magnitude spectrograms from complex and real valued input data. Contains high-level functions, which transform whole DataSets and also add metadata/axis descriptions, but also low level array based functions. For complex input values, the data can be provided as two separate arrays as well as in the "interleaved" layout used by JTransforms.

Author:

Alexander Krimm

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ShortTimeFourierTransform.Padding

Constructor Summary

Constructors

Constructor and Description
ShortTimeFourierTransform()

Method Summary

Modifier and Type	Method and Description
protected static void	apodizeComplex(double[] data, Apodization apodization) Applies the apodization function to data in "interleaved" complex array.
static DataSet	complex(DataSet input, DataSet output, int nFFT, int step, Apodization apodization, ShortTimeFourierTransform.Padding padding, boolean dbScale, boolean truncateDCNy) Perform a Short term fourier transform on complex input data.
static double[][]	complex(double[] complexInput, double[][] output, int nFFT, int step, Apodization apodization, ShortTimeFourierTransform.Padding padding, boolean dbScale, boolean truncateDCNy)
static double[][]	complex(double[] real, double[] imag, double[][] output, int nFFT, int step, Apodization apodization, ShortTimeFourierTransform.Padding padding, boolean dbScale, boolean truncateDCNy)
static double[]	getFrequencyAxisComplex(double dt, int nFFT, double[] output)
static double[]	getFrequencyAxisReal(double dt, int nFFT, double[] output)
static double[]	getTimeAxis(double dt, int nSamples, int step, double[] output)
static DataSet	real(DataSet input, DataSet output, int nFFT, int step, Apodization apodization, ShortTimeFourierTransform.Padding padding, boolean dbScale, boolean truncateDCNy)
static double[][]	real(double[] input, double[][] output, int nFFT, int step, Apodization apodization, ShortTimeFourierTransform.Padding padding, boolean dbScale, boolean truncateDCNy)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ShortTimeFourierTransform

public ShortTimeFourierTransform()

Method Detail

apodizeComplex

protected static void apodizeComplex(double[] data,
                                     Apodization apodization)

Applies the apodization function to data in "interleaved" complex array.

Parameters:

data - an array containing [re1, im1, re2, im2 ... ]

apodization - the apodization window function to use

complex

public static DataSet complex(DataSet input,
                              DataSet output,
                              int nFFT,
                              int step,
                              Apodization apodization,
                              ShortTimeFourierTransform.Padding padding,
                              boolean dbScale,
                              boolean truncateDCNy)

Perform a Short term fourier transform on complex input data. The complex data is expected to be supplied as a DataSet with dim() = 3 with time axis data in DIM_X, real part in DIM_Y and imaginary part in DIM_Z. All dimensions should have the same number of samples.

Parameters:

input - a dataset with equidistantly spaced y(t) = Re(c(t)) and z(t) = data

output - optional output dataset, if not Null, data will be modified in place

nFFT - the number of frequency bins

step - The timestep size in samples

apodization - function, by default Hann window is used

padding - how to pad the slices at the start and end of the time axis: ZERO(default), ZOH or MIRROR

dbScale - true to convert the spectrum to dB scale

truncateDCNy - true to interpolate the DC- and Nyquist-bins to their respective nearest neighbours

Returns:

the spectrogram, a DataSet3D with dimensions [nf = nQuantx x nY = nQuantt]

complex

public static double[][] complex(double[] real,
                                 double[] imag,
                                 double[][] output,
                                 int nFFT,
                                 int step,
                                 Apodization apodization,
                                 ShortTimeFourierTransform.Padding padding,
                                 boolean dbScale,
                                 boolean truncateDCNy)

complex

public static double[][] complex(double[] complexInput,
                                 double[][] output,
                                 int nFFT,
                                 int step,
                                 Apodization apodization,
                                 ShortTimeFourierTransform.Padding padding,
                                 boolean dbScale,
                                 boolean truncateDCNy)

getFrequencyAxisComplex

public static double[] getFrequencyAxisComplex(double dt,
                                               int nFFT,
                                               double[] output)

getFrequencyAxisReal

public static double[] getFrequencyAxisReal(double dt,
                                            int nFFT,
                                            double[] output)

getTimeAxis

public static double[] getTimeAxis(double dt,
                                   int nSamples,
                                   int step,
                                   double[] output)

real

public static DataSet real(DataSet input,
                           DataSet output,
                           int nFFT,
                           int step,
                           Apodization apodization,
                           ShortTimeFourierTransform.Padding padding,
                           boolean dbScale,
                           boolean truncateDCNy)

real

public static double[][] real(double[] input,
                              double[][] output,
                              int nFFT,
                              int step,
                              Apodization apodization,
                              ShortTimeFourierTransform.Padding padding,
                              boolean dbScale,
                              boolean truncateDCNy)