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.conversion;
34
35 import org.openimaj.audio.AudioStream;
36 import org.openimaj.audio.SampleChunk;
37 import org.openimaj.audio.processor.AudioProcessor;
38 import org.openimaj.audio.samples.SampleBuffer;
39 import org.openimaj.audio.samples.SampleBufferFactory;
40
41 /**
42 * Converts a stereo audio stream into a mono one by averaging the
43 * channels' samples and creating a mono sample set. The audio
44 * format of the stream is changed. The process() method creates new
45 * SampleChunks with a new format.
46 *
47 * @author David Dupplaw (dpd@ecs.soton.ac.uk)
48 * @created 10 Jun 2011
49 *
50 */
51 public class MultichannelToMonoProcessor extends AudioProcessor
52 {
53 /**
54 * Create a processor to process chunks.
55 */
56 public MultichannelToMonoProcessor()
57 {
58 }
59
60 /**
61 * Create a processor for the given audio stream. The output
62 * of this audio stream will be a mono stream.
63 *
64 * @param a The audio stream to process.
65 */
66 public MultichannelToMonoProcessor( final AudioStream a )
67 {
68 super( a );
69 this.setFormat( this.getFormat().clone().setNumChannels( 1 ) );
70 }
71
72 /**
73 * {@inheritDoc}
74 * @see org.openimaj.audio.processor.AudioProcessor#process(org.openimaj.audio.SampleChunk)
75 */
76 @Override
77 public SampleChunk process( final SampleChunk sample )
78 {
79 if( sample.getFormat().getNumChannels() == 1 )
80 return sample;
81
82 // Get the samples.
83 final SampleBuffer sb = sample.getSampleBuffer();
84 final int nChannels = sample.getFormat().getNumChannels();
85
86 // Create a new buffer for the mono samples.
87 final SampleBuffer sb2 = SampleBufferFactory.createSampleBuffer(
88 sb.getFormat().clone().setNumChannels( 1 ),
89 sb.size()/nChannels );
90
91 // For all the mono samples...
92 for( int i = 0; i < sb2.size(); i++ )
93 {
94 // Accumulate the sample value
95 double acc = 0;
96 for( int c = 0; c < nChannels; c++ )
97 acc += sb.get(i*nChannels+c);
98
99 // Store the average to the mono channel
100 sb2.set( i, (int)(acc / (double)nChannels) );
101 }
102
103 // Update the samples in the sample chunk
104 return sb2.getSampleChunk();
105 }
106 }