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Mixer: Implement audio stretching

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This commit is contained in:
MerryMage
2017-04-10 17:44:17 +01:00
parent 5b81f2a31d
commit b8c867dd7a
4 changed files with 92 additions and 17 deletions
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77
Source/Core/AudioCommon/Mixer.cpp
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@ -4,6 +4,7 @@
#include "AudioCommon/Mixer.h"
#include <cmath>
#include <cstring>
#include "Common/CommonTypes.h"
@ -15,6 +16,15 @@
CMixer::CMixer(unsigned int BackendSampleRate) : m_sampleRate(BackendSampleRate)
{
INFO_LOG(AUDIO_INTERFACE, "Mixer is initialized");
m_sound_touch.setChannels(2);
m_sound_touch.setSampleRate(BackendSampleRate);
m_sound_touch.setPitch(1.0);
m_sound_touch.setTempo(1.0);
m_sound_touch.setSetting(SETTING_USE_QUICKSEEK, 0);
m_sound_touch.setSetting(SETTING_SEQUENCE_MS, 62);
m_sound_touch.setSetting(SETTING_SEEKWINDOW_MS, 28);
m_sound_touch.setSetting(SETTING_OVERLAP_MS, 8);
}
CMixer::~CMixer()
@ -119,12 +129,73 @@ unsigned int CMixer::Mix(short* samples, unsigned int num_samples, bool consider
memset(samples, 0, num_samples * 2 * sizeof(short));
m_dma_mixer.Mix(samples, num_samples, consider_framelimit);
m_streaming_mixer.Mix(samples, num_samples, consider_framelimit);
m_wiimote_speaker_mixer.Mix(samples, num_samples, consider_framelimit);
unsigned int actual_samples = m_dma_mixer.Mix(samples, num_samples, false);
m_streaming_mixer.Mix(samples, num_samples, false);
m_wiimote_speaker_mixer.Mix(samples, num_samples, false);
StretchAudio(samples, actual_samples, num_samples);
return num_samples;
}
void CMixer::StretchAudio(short* samples, unsigned int actual_samples, unsigned int num_samples)
{
const double time_delta = static_cast<double>(num_samples) / m_sampleRate; // seconds
// We were given actual_samples number of samples, and num_samples were requested from us.
double current_ratio = static_cast<double>(actual_samples) / static_cast<double>(num_samples);
constexpr double MAXIMUM_LATENCY = 0.080; // seconds
const double max_backlog = m_sampleRate * MAXIMUM_LATENCY;
double backlog_fullness = m_sound_touch.numSamples() / max_backlog;
if (backlog_fullness > 1.0)
{
// Exceeded latency budget: Do not add more samples into FIFO.
actual_samples = 0;
}
// We ideally want the backlog to be about 50% full.
// This gives some headroom both ways to prevent underflow and overflow.
// We tweak current_ratio to encourage this.
constexpr double tweak_time_scale = 0.1; // seconds
current_ratio *= 1.0 + 2.0 * (backlog_fullness - 0.5) * (time_delta / tweak_time_scale);
// This low-pass filter smoothes out variance in the calculated stretch ratio.
// The time-scale determines how responsive this filter is.
constexpr double lpf_time_scale = 0.3; // seconds
const double m_lpf_gain = 1.0 - std::exp(-time_delta / lpf_time_scale);
m_stretch_ratio += m_lpf_gain * (current_ratio - m_stretch_ratio);
// Place a lower limit of 10% speed. When a game boots up, there will be
// many silence samples. These do not need to be timestretched.
m_sound_touch.setTempo(std::max(m_stretch_ratio, 0.1));
if (actual_samples != num_samples)
{
DEBUG_LOG(AUDIO, "Audio stretching: samples:%u/%u ratio:%f backlog:%f gain: %f", actual_samples,
num_samples, m_stretch_ratio, backlog_fullness, m_lpf_gain);
}
m_sound_touch.putSamples(samples, actual_samples);
memset(samples, 0, num_samples * 2 * sizeof(short));
const size_t samples_received = m_sound_touch.receiveSamples(samples, num_samples);
if (samples_received != 0)
{
m_last_stretched_sample[0] = samples[samples_received * 2 - 2];
m_last_stretched_sample[1] = samples[samples_received * 2 - 1];
}
// Preform padding if we've run out of samples.
for (size_t i = samples_received; i < num_samples; i++)
{
samples[i * 2 + 0] = m_last_stretched_sample[0];
samples[i * 2 + 1] = m_last_stretched_sample[1];
}
}
void CMixer::MixerFifo::PushSamples(const short* samples, unsigned int num_samples)
{
// Cache access in non-volatile variable