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.util.AudioUtils;
036
037/**
038 *      A Mel triangular filter for frequency spectrum. The class is constructed
039 *      using linear frequencies (Hz) to give the start and end points of the filter.
040 *      These are converted into Mel frequencies (non-linear) so that the triangle
041 *      which is Isosceles in Mel frequency is non-linear in the linear frequency
042 *      (stretched towards the higher frequencies).
043 *
044 *      @author David Dupplaw (dpd@ecs.soton.ac.uk)
045 *  @created 25 Jul 2012
046 *      @version $Author$, $Revision$, $Date$
047 */
048public class MelFilter extends TriangularFilter
049{
050        /**
051         *      The Mel Filter default constructor.
052         *
053         *      @param startFreq The start frequency of the filter
054         *      @param endFreq The end frequency of the filter
055         */
056        public MelFilter( final double startFreq, final double endFreq )
057        {
058                // We need to work out the centre frequency in Mel terms. We work out the
059                // centre frequency in the Mel scale then convert back to linear frequency.
060                super( startFreq, AudioUtils.melFrequencyToFrequency(
061                        (AudioUtils.frequencyToMelFrequency( endFreq ) +
062                         AudioUtils.frequencyToMelFrequency( startFreq )) /2d), endFreq );
063        }
064
065        /**
066         *      {@inheritDoc}
067         *      @see java.lang.Object#toString()
068         */
069        @Override
070        public String toString()
071        {
072                return "mf{"+this.lowFrequency+"->"+this.centreFrequency+"->"+this.highFrequency+"}";
073        }
074}