1 /* 2 * Copyright (c) 2014 The WebRTC project authors. All Rights Reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #define _USE_MATH_DEFINES 12 13 #include "webrtc/common_audio/window_generator.h" 14 15 #include <cmath> 16 #include <complex> 17 18 #include "webrtc/base/checks.h" 19 20 using std::complex; 21 22 namespace { 23 24 // Modified Bessel function of order 0 for complex inputs. 25 complex<float> I0(complex<float> x) { 26 complex<float> y = x / 3.75f; 27 y *= y; 28 return 1.0f + y * ( 29 3.5156229f + y * ( 30 3.0899424f + y * ( 31 1.2067492f + y * ( 32 0.2659732f + y * ( 33 0.360768e-1f + y * 0.45813e-2f))))); 34 } 35 36 } // namespace 37 38 namespace webrtc { 39 40 void WindowGenerator::Hanning(int length, float* window) { 41 RTC_CHECK_GT(length, 1); 42 RTC_CHECK(window != nullptr); 43 for (int i = 0; i < length; ++i) { 44 window[i] = 0.5f * (1 - cosf(2 * static_cast<float>(M_PI) * i / 45 (length - 1))); 46 } 47 } 48 49 void WindowGenerator::KaiserBesselDerived(float alpha, size_t length, 50 float* window) { 51 RTC_CHECK_GT(length, 1U); 52 RTC_CHECK(window != nullptr); 53 54 const size_t half = (length + 1) / 2; 55 float sum = 0.0f; 56 57 for (size_t i = 0; i <= half; ++i) { 58 complex<float> r = (4.0f * i) / length - 1.0f; 59 sum += I0(static_cast<float>(M_PI) * alpha * sqrt(1.0f - r * r)).real(); 60 window[i] = sum; 61 } 62 for (size_t i = length - 1; i >= half; --i) { 63 window[length - i - 1] = sqrtf(window[length - i - 1] / sum); 64 window[i] = window[length - i - 1]; 65 } 66 if (length % 2 == 1) { 67 window[half - 1] = sqrtf(window[half - 1] / sum); 68 } 69 } 70 71 } // namespace webrtc 72 73
