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#include "pch.h"
#include "DspLimiter.h"
namespace SaneAudioRenderer
{
namespace
{
const float slope = 1.0f - 1.0f / 20.0f; // 20:1 ratio
template <typename T>
T GetPeak(const T* data, size_t n)
{
T peak = 0;
for (size_t i = 0; i < n; i++)
peak = std::max(peak, std::abs(data[i]));
return peak;
}
template <typename T>
void ApplyLimiter(T* data, size_t n, T threshold)
{
for (size_t i = 0; i < n; i++)
{
T& sample = data[i];
const T absSample = std::abs(sample);
if (absSample > threshold)
sample *= std::pow(threshold / absSample, slope);
assert(std::abs(sample) <= 1);
}
}
}
void DspLimiter::Initialize(uint32_t rate, uint32_t channels, bool exclusive)
{
m_exclusive = exclusive;
m_rate = rate;
m_channels = channels;
m_active = false;
m_holdWindow = 0;
m_peak = 0.0f;
m_threshold = 0.0f;
}
bool DspLimiter::Active()
{
return m_active;
}
void DspLimiter::Process(DspChunk& chunk)
{
if (chunk.IsEmpty())
return;
if (!m_exclusive || (chunk.GetFormat() != DspFormat::Float &&
chunk.GetFormat() != DspFormat::Double))
{
m_active = false;
return;
}
m_active = true;
// Analyze samples
float peak;
if (chunk.GetFormat() == DspFormat::Double)
{
double largePeak = GetPeak((double*)chunk.GetData(), chunk.GetSampleCount());
peak = std::nexttoward((float)largePeak, largePeak);
}
else
{
assert(chunk.GetFormat() == DspFormat::Float);
peak = GetPeak((float*)chunk.GetData(), chunk.GetSampleCount());
}
// Configure limiter
if (peak > 1.0f)
{
if (m_holdWindow <= 0)
{
NewTreshold(std::max(peak, 1.4f));
}
else if (peak > m_peak)
{
NewTreshold(peak);
}
m_holdWindow = (int64_t)m_rate * m_channels * 10; // 10 seconds
}
// Apply limiter
if (m_holdWindow > 0)
{
if (chunk.GetFormat() == DspFormat::Double)
{
ApplyLimiter<double>((double*)chunk.GetData(), chunk.GetSampleCount(), m_threshold);
}
else
{
assert(chunk.GetFormat() == DspFormat::Float);
ApplyLimiter((float*)chunk.GetData(), chunk.GetSampleCount(), m_threshold);
}
m_holdWindow -= chunk.GetSampleCount();
}
}
void DspLimiter::Finish(DspChunk& chunk)
{
Process(chunk);
}
void DspLimiter::NewTreshold(float peak)
{
m_peak = peak;
m_threshold = std::pow(1.0f / peak, 1.0f / slope - 1.0f) - 0.0001f;
DebugOut("DspLimiter active with", m_peak, "peak and", m_threshold, "threshold");
}
}
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