public class DiscreteFourierTransform extends BaseDataProcessor
By default, the number of FFT points is the closest power of 2 that is equal to or larger than the number of samples
in the incoming window of data. The FFT points can also be set by the user with the property defined by PROP_NUMBER_FFT_POINTS
. The length of the returned power spectrum is the number of FFT points, divided by 2, plus
1. Since the input signal is real, the FFT is symmetric, and the information contained in the whole vector is already
present in its first half.
Note that each call to getData
only returns the spectrum of one window of data. To display the
spectrogram of the entire original audio, one has to collect all the spectra from all the windows generated from the
original data. A spectrogram is a two dimensional representation of three dimensional information. The horizontal
axis represents time. The vertical axis represents the frequency. If we slice the spectrogram at a given time, we get
the spectrum computed as the short term Fourier transform of the signal windowed around that time stamp. The
intensity of the spectrum for each time frame is given by the color in the graph, or by the darkness in a gray scale
plot. The spectrogram can be thought of as a view from the top of a surface generated by concatenating the spectral
vectors obtained from the windowed signal.
For example, Figure 1 below shows the audio signal of the utterance "one three nine oh", and Figure 2 shows its spectrogram, produced by putting together all the spectra returned by this FFT. Frequency is on the vertical axis, and time is on the horizontal axis. The darkness of the shade represents the strength of that frequency at that point in time:
Figure 1: The audio signal of the utterance "one three nine
oh".
Figure 2: The spectrogram of the utterance "one three
nine oh" in Figure 1.
Modifier and Type  Field and Description 

static java.lang.String 
PROP_INVERT
The property for the invert transform.

static java.lang.String 
PROP_NUMBER_FFT_POINTS
The property for the number of points in the Fourier Transform.

Constructor and Description 

DiscreteFourierTransform() 
DiscreteFourierTransform(int numberFftPoints,
boolean invert) 
Modifier and Type  Method and Description 

Data 
getData()
Reads the next DoubleData object, which is a data frame from which we'll compute the power spectrum.

void 
initialize()
Initializes this DataProcessor.

void 
newProperties(PropertySheet ps)
This method is called when this configurable component needs to be reconfigured.

getPredecessor, getTimer, setPredecessor
getName, toString
@S4Integer(defaultValue=1) public static final java.lang.String PROP_NUMBER_FFT_POINTS
@S4Boolean(defaultValue=false) public static final java.lang.String PROP_INVERT
public DiscreteFourierTransform(int numberFftPoints, boolean invert)
public DiscreteFourierTransform()
public void newProperties(PropertySheet ps) throws PropertyException
Configurable
newProperties
in interface Configurable
newProperties
in class ConfigurableAdapter
ps
 a property sheet holding the new dataPropertyException
 if there is a problem with the properties.public void initialize()
BaseDataProcessor
initialize
in interface DataProcessor
initialize
in class BaseDataProcessor
public Data getData() throws DataProcessingException
getData
in interface DataProcessor
getData
in class BaseDataProcessor
DataProcessingException
 if there is a processing error