edu.cmu.sphinx.frontend.frequencywarp

Class PLPFilter

java.lang.Object

edu.cmu.sphinx.frontend.frequencywarp.PLPFilter

public class PLPFilter
extends java.lang.Object

Defines a filter used by the PLPFrequencyFilterBank class. The filter is defined by a function in the Constructor. A set of equally spaced frequencies in a linear scale is passed to the constructor, which returns the weights for each of the frequency bins, such that the filter has the shape defined by this piecewise function in the bark scale.

See Also:

PLPFrequencyFilterBank

Field Summary

Fields

Modifier and Type	Field and Description
double	centerFreqInBark The center frequency of the filter in Bark.
double	centerFreqInHz The center frequency of the filter in Hertz.

Constructor Summary

Constructors

Constructor and Description
PLPFilter(double[] DFTFrequenciesInHz, double centerFreqInHz) Constructs a PLP filter around a given center frequency.

Method Summary

Modifier and Type	Method and Description
double	filterOutput(double[] spectrum) Compute the PLP spectrum at the center frequency of this filter for a given power spectrum.

Methods inherited from class java.lang.Object

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

Field Detail

centerFreqInHz

public final double centerFreqInHz

The center frequency of the filter in Hertz.

centerFreqInBark

public final double centerFreqInBark

The center frequency of the filter in Bark.

Constructor Detail

PLPFilter

public PLPFilter(double[] DFTFrequenciesInHz,
                 double centerFreqInHz)
          throws java.lang.IllegalArgumentException

Constructs a PLP filter around a given center frequency.

Defines a filter according to the following equation, defined piecewise (all frequencies in the equation are Bark frequencies):

 Filter(f) = 0 if f < -2.5 

           = 10^(-(f+0.5)) if -2.5 <= f <= -0.5 

           = 1  if -0.5 <= f <= 0.5 

           = 10^(2.5(f-0.5)) if 0.5 <= f <= 1.3 

           = 0 if f > 1.3 

 

The current implementation assumes that the calling routine passes in an array of frequencies, one for each of the DFT points in the spectrum of the frame of speech to be filtered. This is used in conjunction with a specified center frequency to determine the filter.

Parameters:

DFTFrequenciesInHz - is a double array containing the frequencies in Hertz corresponding to each of the DFT points in the spectrum of the signal to be filtered.

centerFreqInHz - is the filter's center frequency

Throws:

java.lang.IllegalArgumentException - if center frequency is wrong

Method Detail

filterOutput

public double filterOutput(double[] spectrum)
                    throws java.lang.IllegalArgumentException

Compute the PLP spectrum at the center frequency of this filter for a given power spectrum.

Parameters:

spectrum - the input power spectrum to be filtered

Returns:

the PLP spectrum value

Throws:

java.lang.IllegalArgumentException - if the input spectrum is of a different length than the array of filter coefficients