1 /**
2 * Copyright (c) 2011, The University of Southampton and the individual contributors.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without modification,
6 * are permitted provided that the following conditions are met:
7 *
8 * * Redistributions of source code must retain the above copyright notice,
9 * this list of conditions and the following disclaimer.
10 *
11 * * Redistributions in binary form must reproduce the above copyright notice,
12 * this list of conditions and the following disclaimer in the documentation
13 * and/or other materials provided with the distribution.
14 *
15 * * Neither the name of the University of Southampton nor the names of its
16 * contributors may be used to endorse or promote products derived from this
17 * software without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
21 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
22 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
23 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
24 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
25 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
26 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
28 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30 /**
31 *
32 */
33 package org.openimaj.audio.analysis;
34
35 import org.openimaj.audio.SampleChunk;
36 import org.openimaj.audio.processor.AudioProcessor;
37
38 import edu.emory.mathcs.jtransforms.fft.FloatFFT_1D;
39
40 /**
41 * An implementation of the power cepstrum of an audio signal. The
42 * power cepstrum of an audio signal is the squared magnitude of the Fourier
43 * transform of the logarithm of the squared magnitude of the Fourier transform
44 * of a signal. Yeah, I know.
45 *
46 * @author David Dupplaw (dpd@ecs.soton.ac.uk)
47 * @created 18 Jul 2012
48 * @version $Author$, $Revision$, $Date$
49 */
50 public class PowerCepstrumTransform extends AudioProcessor
51 {
52 /** The last generated cepstrum */
53 private float[][] lastCepstrum = null;
54
55 @Override
56 public SampleChunk process( final SampleChunk sample ) throws Exception
57 {
58 final FourierTransform fft = new FourierTransform();
59
60 //
61 // The squared magnitude of the Fourier transform of the logarithm
62 // of the squared magnitude of the Fourier transform of a signal...
63 //
64 // Working backwards...
65 // ... the FFT of a signal...
66 //
67 fft.process( sample );
68 final float[][] fftCoeffs = fft.getLastFFT();
69
70 // ...the logarithm of the squared magnitude...
71 final float logMags[][] = new float[fftCoeffs.length][];
72 for( int c = 0; c < fftCoeffs.length; c++ )
73 {
74 logMags[c] = new float[fftCoeffs[c].length/4];
75 for( int i = 0; i < fftCoeffs[c].length/4; i++ )
76 {
77 // Calculate magnitude
78 final float re = fftCoeffs[c][i*2];
79 final float im = fftCoeffs[c][i*2+1];
80 float mag = (float)Math.log(Math.sqrt( re*re + im*im )+1);
81
82 // Square
83 mag *= mag;
84
85 // Logarithm
86 final float logMag = (float)Math.log( mag );
87
88 // Store
89 logMags[c][i] = logMag;
90 }
91 }
92
93 // ... the Fast Fourier (of the log-squared-mags)
94 this.lastCepstrum = new float[ logMags.length ][];
95 final FloatFFT_1D fft2 = new FloatFFT_1D( logMags[0].length/4 );
96 for( int c = 0; c < logMags.length; c++ )
97 {
98 fft2.complexForward( logMags[c] );
99
100 this.lastCepstrum[c] = new float[ logMags[c].length/4 ];
101
102 // ...the squared magnitude of...
103 for( int i = 0; i < logMags[c].length/4; i++ )
104 {
105 // Calculate magnitude
106 final float re = logMags[c][i*2];
107 final float im = logMags[c][i*2+1];
108 float mag = (float)Math.log(Math.sqrt( re*re + im*im )+1);
109
110 // Square
111 mag *= mag;
112
113 this.lastCepstrum[c][i] = mag;
114 }
115 }
116
117 return sample;
118 }
119
120 /**
121 * Returns the last generated cepstrum
122 * @return The last generated cepstrum
123 */
124 public float[][] getLastCepstrum()
125 {
126 return this.lastCepstrum;
127 }
128 }