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      1 /*
      2  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
      3  *
      4  *  Use of this source code is governed by a BSD-style license
      5  *  that can be found in the LICENSE file in the root of the source
      6  *  tree. An additional intellectual property rights grant can be found
      7  *  in the file PATENTS.  All contributing project authors may
      8  *  be found in the AUTHORS file in the root of the source tree.
      9  */
     10 
     11 #include "webrtc/modules/audio_processing/agc/utility.h"
     12 
     13 #include <math.h>
     14 
     15 static const double kLog10 = 2.30258509299;
     16 static const double kLinear2DbScale = 20.0 / kLog10;
     17 static const double kLinear2LoudnessScale = 13.4 / kLog10;
     18 
     19 double Loudness2Db(double loudness) {
     20   return loudness * kLinear2DbScale / kLinear2LoudnessScale;
     21 }
     22 
     23 double Linear2Loudness(double rms) {
     24   if (rms == 0)
     25     return -15;
     26   return kLinear2LoudnessScale * log(rms);
     27 }
     28 
     29 double Db2Loudness(double db) {
     30   return db * kLinear2LoudnessScale / kLinear2DbScale;
     31 }
     32 
     33 double Dbfs2Loudness(double dbfs) {
     34   return Db2Loudness(90 + dbfs);
     35 }
     36