73 lines
1.9 KiB
C++
73 lines
1.9 KiB
C++
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/*
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* Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#define _USE_MATH_DEFINES
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#include "webrtc/common_audio/window_generator.h"
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#include <cmath>
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#include <complex>
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#include "webrtc/base/checks.h"
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using std::complex;
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namespace {
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// Modified Bessel function of order 0 for complex inputs.
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complex<float> I0(complex<float> x) {
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complex<float> y = x / 3.75f;
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y *= y;
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return 1.0f + y * (
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3.5156229f + y * (
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3.0899424f + y * (
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1.2067492f + y * (
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0.2659732f + y * (
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0.360768e-1f + y * 0.45813e-2f)))));
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}
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} // namespace
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namespace webrtc {
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void WindowGenerator::Hanning(int length, float* window) {
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RTC_CHECK_GT(length, 1);
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RTC_CHECK(window != nullptr);
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for (int i = 0; i < length; ++i) {
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window[i] = 0.5f * (1 - cosf(2 * static_cast<float>(M_PI) * i /
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(length - 1)));
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}
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}
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void WindowGenerator::KaiserBesselDerived(float alpha, size_t length,
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float* window) {
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RTC_CHECK_GT(length, 1U);
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RTC_CHECK(window != nullptr);
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const size_t half = (length + 1) / 2;
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float sum = 0.0f;
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for (size_t i = 0; i <= half; ++i) {
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complex<float> r = (4.0f * i) / length - 1.0f;
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sum += I0(static_cast<float>(M_PI) * alpha * sqrt(1.0f - r * r)).real();
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window[i] = sum;
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}
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for (size_t i = length - 1; i >= half; --i) {
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window[length - i - 1] = sqrtf(window[length - i - 1] / sum);
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window[i] = window[length - i - 1];
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}
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if (length % 2 == 1) {
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window[half - 1] = sqrtf(window[half - 1] / sum);
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}
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}
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} // namespace webrtc
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