1 /* 2 * Copyright (C) 2010, Google Inc. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice, this list of conditions and the following disclaimer. 9 * 2. Redistributions in binary form must reproduce the above copyright 10 * notice, this list of conditions and the following disclaimer in the 11 * documentation and/or other materials provided with the distribution. 12 * 13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY 14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 15 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 16 * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY 17 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 18 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 19 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON 20 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 22 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 23 */ 24 25 #include "config.h" 26 27 #if ENABLE(WEB_AUDIO) 28 29 #include "AudioUtilities.h" 30 #include <wtf/MathExtras.h> 31 32 namespace WebCore { 33 34 namespace AudioUtilities { 35 36 double decibelsToLinear(double decibels) 37 { 38 return pow(10.0, 0.05 * decibels); 39 } 40 41 double linearToDecibels(double linear) 42 { 43 // It's not possible to calculate decibels for a zero linear value since it would be -Inf. 44 // -1000.0 dB represents a very tiny linear value in case we ever reach this case. 45 ASSERT(linear); 46 if (!linear) 47 return -1000.0; 48 49 return 20.0 * log10(linear); 50 } 51 52 double discreteTimeConstantForSampleRate(double timeConstant, double sampleRate) 53 { 54 // hardcoded value is temporary build fix for Windows. 55 // FIXME: replace hardcode 2.718282 with M_E until the correct MathExtras.h solution is determined. 56 return 1.0 - pow(1.0 / 2.718282, 1.0 / (sampleRate * timeConstant)); 57 } 58 59 } // AudioUtilites 60 61 } // WebCore 62 63 #endif // ENABLE(WEB_AUDIO) 64
