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85 lines
2.9 KiB
C++
85 lines
2.9 KiB
C++
// Copyright 2017 Dolphin Emulator Project
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// SPDX-License-Identifier: GPL-2.0-or-later
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#include "AudioCommon/AudioStretcher.h"
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#include <algorithm>
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#include <cmath>
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#include <cstddef>
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#include "Common/Logging/Log.h"
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#include "Core/Config/MainSettings.h"
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namespace AudioCommon
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{
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AudioStretcher::AudioStretcher(unsigned int sample_rate) : m_sample_rate(sample_rate)
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{
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m_sound_touch.setChannels(2);
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m_sound_touch.setSampleRate(sample_rate);
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m_sound_touch.setPitch(1.0);
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m_sound_touch.setTempo(1.0);
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}
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void AudioStretcher::Clear()
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{
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m_sound_touch.clear();
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}
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void AudioStretcher::ProcessSamples(const short* in, unsigned int num_in, unsigned int num_out)
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{
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const double time_delta = static_cast<double>(num_out) / m_sample_rate; // seconds
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// We were given actual_samples number of samples, and num_samples were requested from us.
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double current_ratio = static_cast<double>(num_in) / static_cast<double>(num_out);
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const double max_latency = Config::Get(Config::MAIN_AUDIO_STRETCH_LATENCY);
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const double max_backlog = m_sample_rate * max_latency / 1000.0 / m_stretch_ratio;
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const double backlog_fullness = m_sound_touch.numSamples() / max_backlog;
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if (backlog_fullness > 5.0)
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{
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// Too many samples in backlog: Don't push anymore on
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num_in = 0;
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}
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// We ideally want the backlog to be about 50% full.
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// This gives some headroom both ways to prevent underflow and overflow.
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// We tweak current_ratio to encourage this.
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constexpr double tweak_time_scale = 0.5; // seconds
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current_ratio *= 1.0 + 2.0 * (backlog_fullness - 0.5) * (time_delta / tweak_time_scale);
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// This low-pass filter smoothes out variance in the calculated stretch ratio.
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// The time-scale determines how responsive this filter is.
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constexpr double lpf_time_scale = 1.0; // seconds
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const double lpf_gain = 1.0 - std::exp(-time_delta / lpf_time_scale);
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m_stretch_ratio += lpf_gain * (current_ratio - m_stretch_ratio);
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// Place a lower limit of 10% speed. When a game boots up, there will be
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// many silence samples. These do not need to be timestretched.
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m_stretch_ratio = std::max(m_stretch_ratio, 0.1);
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m_sound_touch.setTempo(m_stretch_ratio);
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DEBUG_LOG_FMT(AUDIO, "Audio stretching: samples:{}/{} ratio:{} backlog:{} gain: {}", num_in,
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num_out, m_stretch_ratio, backlog_fullness, lpf_gain);
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m_sound_touch.putSamples(in, num_in);
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}
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void AudioStretcher::GetStretchedSamples(short* out, unsigned int num_out)
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{
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const size_t samples_received = m_sound_touch.receiveSamples(out, num_out);
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if (samples_received != 0)
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{
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m_last_stretched_sample[0] = out[samples_received * 2 - 2];
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m_last_stretched_sample[1] = out[samples_received * 2 - 1];
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}
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// Perform padding if we've run out of samples.
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for (size_t i = samples_received; i < num_out; i++)
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{
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out[i * 2 + 0] = m_last_stretched_sample[0];
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out[i * 2 + 1] = m_last_stretched_sample[1];
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}
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}
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} // namespace AudioCommon
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