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Spectrum: Templatize various window functions.

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This commit is contained in:
Jared Boone 2016-10-03 12:31:40 -07:00
parent 4153995944
commit b69a3abcb5
1 changed files with 26 additions and 3 deletions
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29
firmware/baseband/spectrum_collector.cpp
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@ -103,6 +103,31 @@ void SpectrumCollector::post_message(const buffer_c16_t& data) {
}
}
template<typename T>
static typename T::value_type spectrum_window_none(const T& s, const size_t i) {
static_assert(power_of_two(s.size()), "Array size must be power of 2");
return s[i];
};
template<typename T>
static typename T::value_type spectrum_window_hamming_3(const T& s, const size_t i) {
static_assert(power_of_two(s.size()), "Array size must be power of 2");
constexpr size_t mask = s.size() - 1;
// Three point Hamming window.
return s[i] * 0.54f + (s[(i-1) & mask] + s[(i+1) & mask]) * -0.23f;
};
template<typename T>
static typename T::value_type spectrum_window_blackman_3(const T& s, const size_t i) {
static_assert(power_of_two(s.size()), "Array size must be power of 2");
constexpr size_t mask = s.size() - 1;
// Three term Blackman window.
constexpr float alpha = 0.42f;
constexpr float beta = 0.5f * 0.5f;
constexpr float gamma = 0.08f * 0.05f;
return s[i] * alpha - (s[(i-1) & mask] + s[(i+1) & mask]) * beta + (s[(i-2) & mask] + s[(i+2) & mask]) * gamma;
};
void SpectrumCollector::update() {
// Called from idle thread (after EVT_MASK_SPECTRUM is flagged)
if( streaming && channel_spectrum_request_update ) {
@ -114,9 +139,7 @@ void SpectrumCollector::update() {
spectrum.channel_filter_pass_frequency = channel_filter_pass_frequency;
spectrum.channel_filter_stop_frequency = channel_filter_stop_frequency;
for(size_t i=0; i<spectrum.db.size(); i++) {
// Three point Hamming window.
const auto corrected_sample = channel_spectrum[i] * 0.54f
+ (channel_spectrum[(i-1) & 0xff] + channel_spectrum[(i+1) & 0xff]) * -0.23f;
const auto corrected_sample = spectrum_window_hamming_3(channel_spectrum, i);
const auto mag2 = magnitude_squared(corrected_sample * (1.0f / 32768.0f));
const float db = mag2_to_dbv_norm(mag2);
constexpr float mag_scale = 5.0f;