Package icyllis.modernui.audio

Class FFT

java.lang.Object
icyllis.modernui.audio.FFT
public class FFT extends Object
Provides Fast Fourier Transform. It is an efficient way to calculate the Complex Discrete Fourier Transform, which is commonly used to analyze the spectrum of an audio buffer.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    BARTLETT
     
    static final int
    BLACKMAN
     
    static final int
    HAMMING
     
    static final int
    HANN
     
    static final int
    NONE
    Constants indicating which window should be used on sample buffers.

  • Method Summary

    Modifier and Type
    Method
    Description
    static FFT
    create(int timeSize, int sampleRate)
    Creates an FFT that will accept sample buffers that are timeSize long and have been recorded with a sample rate of sampleRate.
    void
    forward(float[] real, float[] imag, int offset)
    Performs a forward transform on the passed buffers.
    void
    forward(float[] samples, int offset)
    Performs a forward transform on values in samples.
    int
    freqToIndex(float freq)
    Returns the index of the frequency band that contains the requested frequency.
    float
    getAverage(float lowFreq, float hiFreq)
    Calculate the average amplitude of the frequency band bounded by lowFreq and hiFreq, inclusive.
    float
    getAverage(int i)
    Gets the value of the ith average.
    float
    getAverageCenterFrequency(int i)
    Returns the center frequency of the ith average band.
    int
    getAverageSize()
    Returns the number of averages currently being calculated.
    float
    getBand(int i)
    Returns the amplitude of the requested frequency band.
    int
    getBandSize()
    Returns the size of the spectrum created by this transform.
    float
    getBandWidth()
    Returns the width of each frequency band in the spectrum (in Hz).
    float
    getFrequency(float freq)
    Gets the amplitude of the requested frequency in the spectrum.
    int
    getSampleRate()
    Returns the sample rate of signal samples expected by this transform.
    int
    getTimeSize()
    Returns the length of the time domain signal expected by this transform.
    float
    indexToFreq(int i)
    Returns the middle frequency of the ith band.
    void
    scaleBand(int band, float scale)
    Scales the amplitude of the ith frequency band by s.
    void
    scaleFrequency(float freq, float scale)
    Scales the amplitude of the requested frequency by a.
    void
    setBand(int band, float amplitude)
    Sets the amplitude of the ith frequency band to a.
    void
    setFrequency(float freq, float amplitude)
    Sets the amplitude of the requested frequency in the spectrum to a.
    void
    setLinearAverages(int num)
    Sets the number of averages used when computing the spectrum and spaces the averages in a linear manner.
    void
    setLogAverages(int minBandwidth, int bandsPerOctave)
    Sets the number of averages used when computing the spectrum based on the minimum bandwidth for an octave and the number of bands per octave.
    void
    setNoAverages()
    Sets the object to not compute averages.
    void
    setWindowFunc(int func)
    Sets the window to use on the samples before taking the forward transform.

    Methods inherited from class java.lang.Object

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

  • Field Details

  • Method Details

    • create

      @Nonnull public static FFT create(int timeSize, int sampleRate)
      Creates an FFT that will accept sample buffers that are timeSize long and have been recorded with a sample rate of sampleRate. timeSize must be a power of two.
      Parameters:
      timeSize - the length of the sample buffers you will be analyzing
      sampleRate - the sample rate of the audio you will be analyzing

    • forward

      public void forward(@Nonnull float[] samples, int offset)
      Performs a forward transform on values in samples.
      Parameters:
      samples - the buffer of samples
      offset - the offset to start at in the buffer, the exceeded part of next timeSize() samples from the starting index in the buffer will be filled with zeros.

    • forward

      public void forward(@Nonnull float[] real, @Nonnull float[] imag, int offset)
      Performs a forward transform on the passed buffers.
      Parameters:
      real - the real part of the time domain signal to transform
      imag - the imaginary part of the time domain signal to transform
      offset - the offset to start at in the buffer, the exceeded part of next timeSize() * samples from the starting index in the buffer will be filled with zeros.

    • setNoAverages

      public void setNoAverages()
      Sets the object to not compute averages.

    • setLinearAverages

      public void setLinearAverages(int num)
      Sets the number of averages used when computing the spectrum and spaces the averages in a linear manner. In other words, each average band will be specSize() / numAvg bands wide.
      Parameters:
      num - how many averages to compute

    • setLogAverages

      public void setLogAverages(int minBandwidth, int bandsPerOctave)
      Sets the number of averages used when computing the spectrum based on the minimum bandwidth for an octave and the number of bands per octave. For example, with audio that has a sample rate of 44100 Hz, logAverages(11, 1) will result in 12 averages, each corresponding to an octave, the first spanning 0 to 11 Hz. To ensure that each octave band is a full octave, the number of octaves is computed by dividing the Nyquist frequency by two, and then the result of that by two, and so on. This means that the actual bandwidth of the lowest octave may not be exactly the value specified.
      Parameters:
      minBandwidth - the minimum bandwidth used for an octave
      bandsPerOctave - how many bands to split each octave into

    • setWindowFunc

      public void setWindowFunc(int func)
      Sets the window to use on the samples before taking the forward transform. If an invalid window is asked for, an error will be reported and the current window will not be changed. NONE is the default, equivalent to the rectangular window.
      Parameters:
      func - window function, such as HAMMING
      Throws:
      IllegalArgumentException - invalid window function

    • getTimeSize

      public int getTimeSize()
      Returns the length of the time domain signal expected by this transform.
      Returns:
      the length of the time domain signal expected by this transform

    • getSampleRate

      public int getSampleRate()
      Returns the sample rate of signal samples expected by this transform.
      Returns:
      the sample rate of signal samples expected by this transform

    • getBandSize

      public int getBandSize()
      Returns the size of the spectrum created by this transform. In other words, the number of frequency bands produced by this transform. This is typically equal to timeSize()/2 + 1, see above for an explanation.
      Returns:
      the size of the spectrum

    • getBandWidth

      public float getBandWidth()
      Returns the width of each frequency band in the spectrum (in Hz). It should be noted that the bandwidth of the first and last frequency bands is half as large as the value returned by this function.
      Returns:
      the width of each frequency band in Hz.

    • getBand

      public float getBand(int i)
      Returns the amplitude of the requested frequency band.
      Parameters:
      i - the index of a frequency band
      Returns:
      the amplitude of the requested frequency band

    • setBand

      public void setBand(int band, float amplitude)
      Sets the amplitude of the ith frequency band to a. You can use this to shape the spectrum before using inverse().
      Parameters:
      band - the frequency band to modify
      amplitude - the new amplitude

    • scaleBand

      public void scaleBand(int band, float scale)
      Scales the amplitude of the ith frequency band by s. You can use this to shape the spectrum before using inverse().
      Parameters:
      band - the frequency band to modify
      scale - the scaling factor

    • freqToIndex

      public int freqToIndex(float freq)
      Returns the index of the frequency band that contains the requested frequency.
      Parameters:
      freq - the frequency you want the index for (in Hz)
      Returns:
      the index of the frequency band that contains freq

    • indexToFreq

      public float indexToFreq(int i)
      Returns the middle frequency of the ith band.
      Parameters:
      i - the index of the band you want to middle frequency of

    • getAverageCenterFrequency

      public float getAverageCenterFrequency(int i)
      Returns the center frequency of the ith average band.
      Parameters:
      i - which average band you want the center frequency of.

    • getFrequency

      public float getFrequency(float freq)
      Gets the amplitude of the requested frequency in the spectrum.
      Parameters:
      freq - the frequency in Hz
      Returns:
      the amplitude of the frequency in the spectrum

    • setFrequency

      public void setFrequency(float freq, float amplitude)
      Sets the amplitude of the requested frequency in the spectrum to a.
      Parameters:
      freq - the frequency in Hz
      amplitude - the new amplitude

    • scaleFrequency

      public void scaleFrequency(float freq, float scale)
      Scales the amplitude of the requested frequency by a.
      Parameters:
      freq - the frequency in Hz
      scale - the scaling factor

    • getAverageSize

      public int getAverageSize()
      Returns the number of averages currently being calculated.
      Returns:
      the length of the averages array

    • getAverage

      public float getAverage(int i)
      Gets the value of the ith average.
      Parameters:
      i - the average you want the value of
      Returns:
      the value of the requested average band

    • getAverage

      public float getAverage(float lowFreq, float hiFreq)
      Calculate the average amplitude of the frequency band bounded by lowFreq and hiFreq, inclusive.
      Parameters:
      lowFreq - the lower bound of the band
      hiFreq - the upper bound of the band
      Returns:
      the average of all spectrum values within the bounds