diff --git a/src/audio_core/CMakeLists.txt b/src/audio_core/CMakeLists.txt index 869da5e83f..b1c86462fc 100644 --- a/src/audio_core/CMakeLists.txt +++ b/src/audio_core/CMakeLists.txt @@ -4,6 +4,7 @@ set(SRCS hle/dsp.cpp hle/filter.cpp hle/pipe.cpp + interpolate.cpp ) set(HEADERS @@ -13,6 +14,7 @@ set(HEADERS hle/dsp.h hle/filter.h hle/pipe.h + interpolate.h sink.h ) diff --git a/src/audio_core/interpolate.cpp b/src/audio_core/interpolate.cpp new file mode 100644 index 0000000000..fcd3aa0660 --- /dev/null +++ b/src/audio_core/interpolate.cpp @@ -0,0 +1,85 @@ +// Copyright 2016 Citra Emulator Project +// Licensed under GPLv2 or any later version +// Refer to the license.txt file included. + +#include "audio_core/interpolate.h" + +#include "common/assert.h" +#include "common/math_util.h" + +namespace AudioInterp { + +// Calculations are done in fixed point with 24 fractional bits. +// (This is not verified. This was chosen for minimal error.) +constexpr u64 scale_factor = 1 << 24; +constexpr u64 scale_mask = scale_factor - 1; + +/// Here we step over the input in steps of rate_multiplier, until we consume all of the input. +/// Three adjacent samples are passed to fn each step. +template +static StereoBuffer16 StepOverSamples(State& state, const StereoBuffer16& input, float rate_multiplier, Function fn) { + ASSERT(rate_multiplier > 0); + + if (input.size() < 2) + return {}; + + StereoBuffer16 output; + output.reserve(static_cast(input.size() / rate_multiplier)); + + u64 step_size = static_cast(rate_multiplier * scale_factor); + + u64 fposition = 0; + const u64 max_fposition = input.size() * scale_factor; + + while (fposition < 1 * scale_factor) { + u64 fraction = fposition & scale_mask; + + output.push_back(fn(fraction, state.xn2, state.xn1, input[0])); + + fposition += step_size; + } + + while (fposition < 2 * scale_factor) { + u64 fraction = fposition & scale_mask; + + output.push_back(fn(fraction, state.xn1, input[0], input[1])); + + fposition += step_size; + } + + while (fposition < max_fposition) { + u64 fraction = fposition & scale_mask; + + size_t index = static_cast(fposition / scale_factor); + output.push_back(fn(fraction, input[index - 2], input[index - 1], input[index])); + + fposition += step_size; + } + + state.xn2 = input[input.size() - 2]; + state.xn1 = input[input.size() - 1]; + + return output; +} + +StereoBuffer16 None(State& state, const StereoBuffer16& input, float rate_multiplier) { + return StepOverSamples(state, input, rate_multiplier, [](u64 fraction, const auto& x0, const auto& x1, const auto& x2) { + return x0; + }); +} + +StereoBuffer16 Linear(State& state, const StereoBuffer16& input, float rate_multiplier) { + // Note on accuracy: Some values that this produces are +/- 1 from the actual firmware. + return StepOverSamples(state, input, rate_multiplier, [](u64 fraction, const auto& x0, const auto& x1, const auto& x2) { + // This is a saturated subtraction. (Verified by black-box fuzzing.) + s64 delta0 = MathUtil::Clamp(x1[0] - x0[0], -32768, 32767); + s64 delta1 = MathUtil::Clamp(x1[1] - x0[1], -32768, 32767); + + return std::array { + static_cast(x0[0] + fraction * delta0 / scale_factor), + static_cast(x0[1] + fraction * delta1 / scale_factor) + }; + }); +} + +} // namespace AudioInterp diff --git a/src/audio_core/interpolate.h b/src/audio_core/interpolate.h new file mode 100644 index 0000000000..a4c0a453d6 --- /dev/null +++ b/src/audio_core/interpolate.h @@ -0,0 +1,41 @@ +// Copyright 2016 Citra Emulator Project +// Licensed under GPLv2 or any later version +// Refer to the license.txt file included. + +#pragma once + +#include +#include + +#include "common/common_types.h" + +namespace AudioInterp { + +/// A variable length buffer of signed PCM16 stereo samples. +using StereoBuffer16 = std::vector>; + +struct State { + // Two historical samples. + std::array xn1 = {}; ///< x[n-1] + std::array xn2 = {}; ///< x[n-2] +}; + +/** + * No interpolation. This is equivalent to a zero-order hold. There is a two-sample predelay. + * @param input Input buffer. + * @param rate_multiplier Stretch factor. Must be a positive non-zero value. + * rate_multiplier > 1.0 performs decimation and rate_multipler < 1.0 performs upsampling. + * @return The resampled audio buffer. + */ +StereoBuffer16 None(State& state, const StereoBuffer16& input, float rate_multiplier); + +/** + * Linear interpolation. This is equivalent to a first-order hold. There is a two-sample predelay. + * @param input Input buffer. + * @param rate_multiplier Stretch factor. Must be a positive non-zero value. + * rate_multiplier > 1.0 performs decimation and rate_multipler < 1.0 performs upsampling. + * @return The resampled audio buffer. + */ +StereoBuffer16 Linear(State& state, const StereoBuffer16& input, float rate_multiplier); + +} // namespace AudioInterp