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/*
* Copyright (c) 2020-2023 Vasile Vilvoiu <vasi@vilvoiu.ro>
*
* specgram is free software; you can redistribute it and/or modify
* it under the terms of the MIT license. See LICENSE for details.
*/
#include "window-function.hpp"
#include <cassert>
WindowFunction::WindowFunction(std::size_t window_size) : window_size_(window_size)
{
cached_factors_.resize(window_size);
}
std::unique_ptr<WindowFunction>
WindowFunction::Build(WindowFunctionType type, std::size_t window_size)
{
switch (type) {
case WindowFunctionType::kNone:
return nullptr; /* no window needed */
case WindowFunctionType::kHann:
return std::make_unique<HannWindowFunction>(window_size);
case WindowFunctionType::kHamming:
return std::make_unique<HammingWindowFunction>(window_size);
case WindowFunctionType::kBlackman:
return std::make_unique<BlackmanWindowFunction>(window_size);
case WindowFunctionType::kNuttall:
return std::make_unique<NuttallWindowFunction>(window_size);
default:
throw std::runtime_error("unknown window function");
}
}
ComplexWindow
WindowFunction::Apply(const ComplexWindow& window) const
{
/* only matching windows */
if (window.size() != this->window_size_) {
throw std::runtime_error("incorrect window size for window function application");
}
assert(this->cached_factors_.size() == this->window_size_);
ComplexWindow output;
output.resize(this->window_size_);
for (std::size_t i = 0; i < this->window_size_; i++) {
output[i] = window[i] * this->cached_factors_[i];
}
return output;
}
GeneralizedCosineWindowFunction::GeneralizedCosineWindowFunction(std::size_t window_size,
const std::vector<double>& a)
: WindowFunction(window_size)
{
if (this->window_size_ == 1) {
/* noop case */
this->cached_factors_[0] = 1.0;
return;
}
double N = (double)this->window_size_ - 1.0;
for (std::size_t n = 0; n < this->window_size_; n++) {
this->cached_factors_[n] = 0;
for (unsigned int k = 0; k < a.size(); k++) {
this->cached_factors_[n] +=
std::pow<double>(-1.0f, k) * a[k] * std::cos(2.0 * (double)M_PI * k * (double)n / N);
}
}
}
HannWindowFunction::HannWindowFunction(std::size_t window_size)
: GeneralizedCosineWindowFunction(window_size, { 0.5, 0.5 })
{
}
HammingWindowFunction::HammingWindowFunction(std::size_t window_size)
: GeneralizedCosineWindowFunction(window_size, { 0.54, 0.46 })
{
}
BlackmanWindowFunction::BlackmanWindowFunction(std::size_t window_size)
: GeneralizedCosineWindowFunction(window_size, { 0.42, 0.5, 0.08 })
{
}
NuttallWindowFunction::NuttallWindowFunction(std::size_t window_size)
: GeneralizedCosineWindowFunction(window_size, { 0.3635819, 0.4891775, 0.1365995, 0.0106411 })
{
}
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