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      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 "platform/audio/AudioUtilities.h"
     30 
     31 #include "wtf/Assertions.h"
     32 #include "wtf/MathExtras.h"
     33 
     34 namespace blink {
     35 
     36 namespace AudioUtilities {
     37 
     38 float decibelsToLinear(float decibels)
     39 {
     40     return powf(10, 0.05f * decibels);
     41 }
     42 
     43 float linearToDecibels(float linear)
     44 {
     45     // It's not possible to calculate decibels for a zero linear value since it would be -Inf.
     46     // -1000.0 dB represents a very tiny linear value in case we ever reach this case.
     47     ASSERT(linear);
     48     if (!linear)
     49         return -1000;
     50 
     51     return 20 * log10f(linear);
     52 }
     53 
     54 double discreteTimeConstantForSampleRate(double timeConstant, double sampleRate)
     55 {
     56     return 1 - exp(-1 / (sampleRate * timeConstant));
     57 }
     58 
     59 size_t timeToSampleFrame(double time, double sampleRate)
     60 {
     61     return static_cast<size_t>(round(time * sampleRate));
     62 }
     63 
     64 bool isValidAudioBufferSampleRate(float sampleRate)
     65 {
     66     return sampleRate >= minAudioBufferSampleRate() && sampleRate <= maxAudioBufferSampleRate();
     67 }
     68 
     69 float minAudioBufferSampleRate()
     70 {
     71     // crbug.com/344375
     72     return 3000;
     73 }
     74 
     75 float maxAudioBufferSampleRate()
     76 {
     77     // Windows can support audio sampling rates this high, so allow AudioBuffer rates this high as well.
     78     return 192000;
     79 }
     80 } // AudioUtilites
     81 
     82 } // namespace blink
     83 
     84 #endif // ENABLE(WEB_AUDIO)
     85