001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030/**
031 * 
032 */
033package org.openimaj.audio.filters;
034
035import org.openimaj.audio.AudioStream;
036import org.openimaj.audio.SampleChunk;
037import org.openimaj.audio.processor.AudioProcessor;
038import org.openimaj.audio.samples.SampleBuffer;
039
040/**
041 *      A simple preemphasiser that applies a high-pass filter to the the audio
042 *      for speech signals. It's basically a really simple comb filter.
043 *
044 *      @author David Dupplaw (dpd@ecs.soton.ac.uk)
045 *  @created 13 Aug 2012
046 *      @version $Author$, $Revision$, $Date$
047 */
048public class Preemphasiser extends AudioProcessor
049{
050        /** Default preemphasis factor */
051        private double factor = 0.97;
052        
053        /**
054         *      Default constructor
055         */
056        public Preemphasiser()
057    {
058    }
059        
060        /**
061         *      Constructor that takes the emphasis factor.
062         *      @param factor The emphasis factor
063         */
064        public Preemphasiser( final double factor )
065        {
066                this.factor = factor;
067        }
068        
069        /**
070         *      Chainiable constructor
071         *      @param as The stream to chain to
072         */
073        public Preemphasiser( final AudioStream as )
074        {
075                super( as );
076        }
077        
078        /**
079         *      Chainable constructor that takes the emphasis factor.
080         *      @param as The stream to chain to
081         *      @param factor The emphasis factor
082         */
083        public Preemphasiser( final AudioStream as, final double factor )
084        {
085                this( as );
086                this.factor = factor;
087        }
088        
089        /** 
090         *      {@inheritDoc}
091         *      @see org.openimaj.audio.processor.AudioProcessor#process(org.openimaj.audio.SampleChunk)
092         */
093        @Override
094        public SampleChunk process( final SampleChunk sample ) throws Exception
095        {
096                final SampleBuffer sb = sample.getSampleBuffer();
097                final int nc = sb.getFormat().getNumChannels();
098                for( int c = 0; c < nc; c++ )
099                {
100                        float previous = 0;
101                        for( int s = 1; s < sb.size()/nc; s++ )
102                        {
103                                final float v = sb.get(s*c);
104                                sb.set( s*c, (float)(v - this.factor * previous) );
105                                previous = v;
106                        }
107                }
108                
109                return sample;
110        }
111}