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Use IFIR decimation for broadcast FM receiver.

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This commit is contained in:
Jared Boone
2016-01-02 10:35:23 -08:00
parent a02bfe55d0
commit e720bfb054
5 changed files with 67 additions and 23 deletions
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41
firmware/baseband/proc_wfm_audio.cpp
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@@ -23,8 +23,34 @@
#include <cstdint>
WidebandFMAudio::WidebandFMAudio() {
constexpr size_t baseband_fs = 3072000;
constexpr size_t decim_0_input_fs = baseband_fs;
constexpr size_t decim_0_decimation_factor = 4;
constexpr size_t decim_0_output_fs = decim_0_input_fs / decim_0_decimation_factor;
constexpr size_t decim_1_input_fs = decim_0_output_fs;
constexpr size_t decim_1_decimation_factor = 2;
constexpr size_t decim_1_output_fs = decim_1_input_fs / decim_1_decimation_factor;
constexpr size_t demod_input_fs = decim_1_output_fs;
decim_0.configure(taps_200k_wfm_decim_0.taps, 33554432);
decim_1.configure(taps_200k_wfm_decim_1.taps, 131072);
demod.configure(demod_input_fs, 75000);
audio_filter.configure(taps_64_lp_156_198.taps);
}
void WidebandFMAudio::execute(const buffer_c8_t& buffer) {
auto decimator_out = decimator.execute(buffer);
const buffer_c16_t dst_buffer {
dst.data(),
dst.size()
};
const auto decim_0_out = decim_0.execute(buffer, dst_buffer);
const auto decim_1_out = decim_1.execute(decim_0_out, dst_buffer);
const auto decimator_out = decim_1_out;
const buffer_s16_t work_audio_buffer {
(int16_t*)decimator_out.p,
@@ -37,29 +63,24 @@ void WidebandFMAudio::execute(const buffer_c8_t& buffer) {
feed_channel_stats(channel);
//feed_channel_spectrum(channel);
/* 768kHz complex<int16_t>[512]
/* 384kHz complex<int16_t>[256]
* -> FM demodulation
* -> 768kHz int16_t[512] */
* -> 384kHz int16_t[256] */
/* TODO: To improve adjacent channel rejection, implement complex channel filter:
* pass < +/- 100kHz, stop > +/- 200kHz
*/
auto audio_oversampled = demod.execute(decimator_out, work_audio_buffer);
/* 768kHz int16_t[512]
* -> 4th order CIC decimation by 2, gain of 1
* -> 384kHz int16_t[256] */
auto audio_8fs = audio_dec_1.execute(audio_oversampled, work_audio_buffer);
/* 384kHz int16_t[256]
* -> 4th order CIC decimation by 2, gain of 1
* -> 192kHz int16_t[128] */
auto audio_4fs = audio_dec_2.execute(audio_8fs, work_audio_buffer);
auto audio_4fs = audio_dec_1.execute(audio_oversampled, work_audio_buffer);
/* 192kHz int16_t[128]
* -> 4th order CIC decimation by 2, gain of 1
* -> 96kHz int16_t[64] */
auto audio_2fs = audio_dec_3.execute(audio_4fs, work_audio_buffer);
auto audio_2fs = audio_dec_2.execute(audio_4fs, work_audio_buffer);
/* 96kHz int16_t[64]
* -> FIR filter, <15kHz (0.156fs) pass, >19kHz (0.198fs) stop, gain of 1