Gain.h

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/**********************************************************************
 
  Audacity: A Digital Audio Editor
 
  Gain.h
 
  Dmitry Vedenko
 
**********************************************************************/
 
#pragma once
 
#include <type_traits>
#include <cmath>
#include <limits>
 
// Implementation is based on https://www.dr-lex.be/info-stuff/volumecontrols.html
template<typename Type>
Type ExpGain(Type gain) noexcept
{
   static_assert(std::is_floating_point_v<Type>);
 
   constexpr Type a(1e-3);
   constexpr Type b(6.908);
 
   if (gain < std::numeric_limits<Type>::epsilon())
      return {};
 
   const Type expGain = a * std::exp(b * gain);
 
   if (expGain > Type(1))
      return Type(1);
 
   return expGain;
}