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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021, kleines Filmröllchen <filmroellchen@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Math.h>
namespace Audio {
using AK::Exponentials::exp;
using AK::Exponentials::log;
// Constants for logarithmic volume. See Sample::linear_to_log
// Corresponds to 60dB
constexpr double DYNAMIC_RANGE = 1000;
constexpr double VOLUME_A = 1 / DYNAMIC_RANGE;
double const VOLUME_B = log(DYNAMIC_RANGE);
// A single sample in an audio buffer.
// Values are floating point, and should range from -1.0 to +1.0
struct Sample {
constexpr Sample() = default;
// For mono
constexpr explicit Sample(double left)
: left(left)
, right(left)
{
}
// For stereo
constexpr Sample(double left, double right)
: left(left)
, right(right)
{
}
void clip()
{
if (left > 1)
left = 1;
else if (left < -1)
left = -1;
if (right > 1)
right = 1;
else if (right < -1)
right = -1;
}
// Logarithmic scaling, as audio should ALWAYS do.
// Reference: https://www.dr-lex.be/info-stuff/volumecontrols.html
// We use the curve `factor = a * exp(b * change)`,
// where change is the input fraction we want to change by,
// a = 1/1000, b = ln(1000) = 6.908 and factor is the multiplier used.
// The value 1000 represents the dynamic range in sound pressure, which corresponds to 60 dB(A).
// This is a good dynamic range because it can represent all loudness values from
// 30 dB(A) (barely hearable with background noise)
// to 90 dB(A) (almost too loud to hear and about the reasonable limit of actual sound equipment).
//
// Format ranges:
// - Linear: 0.0 to 1.0
// - Logarithmic: 0.0 to 1.0
ALWAYS_INLINE double linear_to_log(double const change) const
{
// TODO: Add linear slope around 0
return VOLUME_A * exp(VOLUME_B * change);
}
ALWAYS_INLINE double log_to_linear(double const val) const
{
// TODO: Add linear slope around 0
return log(val / VOLUME_A) / VOLUME_B;
}
ALWAYS_INLINE Sample& log_multiply(double const change)
{
double factor = linear_to_log(change);
left *= factor;
right *= factor;
return *this;
}
ALWAYS_INLINE Sample log_multiplied(double const volume_change) const
{
Sample new_frame { left, right };
new_frame.log_multiply(volume_change);
return new_frame;
}
// Constant power panning
ALWAYS_INLINE Sample& pan(double const position)
{
double const pi_over_2 = AK::Pi<double> * 0.5;
double const root_over_2 = AK::sqrt(2.0) * 0.5;
double const angle = position * pi_over_2 * 0.5;
double s, c;
AK::sincos(angle, s, c);
left *= root_over_2 * (c - s);
right *= root_over_2 * (c + s);
return *this;
}
ALWAYS_INLINE Sample panned(double const position) const
{
Sample new_sample { left, right };
new_sample.pan(position);
return new_sample;
}
constexpr Sample& operator*=(double const mult)
{
left *= mult;
right *= mult;
return *this;
}
constexpr Sample operator*(double const mult) const
{
return { left * mult, right * mult };
}
constexpr Sample& operator+=(Sample const& other)
{
left += other.left;
right += other.right;
return *this;
}
constexpr Sample& operator+=(double other)
{
left += other;
right += other;
return *this;
}
constexpr Sample operator+(Sample const& other) const
{
return { left + other.left, right + other.right };
}
double left { 0 };
double right { 0 };
};
}
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