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Move baseband FIR filter defs to common file.

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They will likely be shared with multiple decimators/demodulators.
Also added normalized filter pass/stop values to each set of taps.
This commit is contained in:
Jared Boone 2015-12-30 12:19:42 -08:00
parent 3db0820b54
commit 7de80edcd3
3 changed files with 132 additions and 230 deletions
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35
firmware/baseband/proc_am_audio.cpp
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@ -21,31 +21,6 @@
#include "proc_am_audio.hpp"
// DSB AM 6K00A3E emission type ///////////////////////////////////////////
// IFIR image-reject filter: fs=3072000, pass=3000, stop=339000, decim=8, fout=384000
static constexpr std::array<int16_t, 24> taps_6k0_decim_0 { {
39, 104, 224, 412, 674, 1008, 1400, 1821,
2234, 2594, 2863, 3006, 3006, 2863, 2594, 2234,
1821, 1400, 1008, 674, 412, 224, 104, 39,
} };
// IFIR prototype filter: fs=384000, pass=3000, stop=45000, decim=8, fout=48000
static constexpr std::array<int16_t, 32> taps_6k0_decim_1 { {
-26, -63, -123, -195, -263, -295, -253, -99,
199, 651, 1242, 1927, 2633, 3273, 3760, 4023,
4023, 3760, 3273, 2633, 1927, 1242, 651, 199,
-99, -253, -295, -263, -195, -123, -63, -26,
} };
// Channel filter: fs=48000, pass=3000, stop=6700, decim=1, fout=48000
static constexpr std::array<int16_t, 32> taps_6k0_channel { {
95, 178, 247, 208, -21, -474, -1080, -1640,
-1857, -1411, -83, 2134, 4978, 7946, 10413, 11815,
11815, 10413, 7946, 4978, 2134, -83, -1411, -1857,
-1640, -1080, -474, -21, 208, 247, 178, 95,
} };
NarrowbandAMAudio::NarrowbandAMAudio() {
constexpr size_t baseband_fs = 3072000;
@ -61,11 +36,11 @@ NarrowbandAMAudio::NarrowbandAMAudio() {
constexpr size_t channel_filter_decimation_factor = 1;
constexpr size_t channel_filter_output_fs = channel_filter_input_fs / channel_filter_decimation_factor;
decim_0.configure(taps_6k0_decim_0, 33554432);
decim_1.configure(taps_6k0_decim_1, 131072);
channel_filter.configure(taps_6k0_channel, 1);
channel_filter_pass_f = 3000;
channel_filter_stop_f = 6700;
decim_0.configure(taps_6k0_decim_0.taps, 33554432);
decim_1.configure(taps_6k0_decim_1.taps, 131072);
channel_filter.configure(taps_6k0_channel.taps, 1);
channel_filter_pass_f = taps_6k0_channel.pass_frequency_normalized * channel_filter_input_fs;
channel_filter_stop_f = taps_6k0_channel.stop_frequency_normalized * channel_filter_input_fs;
channel_spectrum.set_decimation_factor(std::floor((channel_filter_output_fs / 2) / ((channel_filter_pass_f + channel_filter_stop_f) / 2)));
}