Rebake of AM, NFM demodulators -- more flexible filtering/configuration.

Also make SpectrumCollector dynamically configurable.
Add deemphasis filter to NFM.

firmware/baseband/dsp_iir_config.hpp

@@ -34,6 +34,12 @@ constexpr iir_biquad_config_t audio_hpf_config {
 constexpr iir_biquad_config_t non_audio_hpf_config {
 	{  0.51891061f, -0.95714180f,  0.51891061f },
 	{  1.0f       , -0.79878302f,  0.43960231f }
+
+// scipy.signal.butter(1, 300 / 24000.0, 'lowpass', analog=False)
+// NOTE: Technically, order-1 filter, b[2] = a[2] = 0.
+constexpr iir_biquad_config_t audio_deemph_300_6_config {
+	{  0.01925927f,  0.01925927f,  0.00000000f, },
+	{  1.00000000f, -0.96148145f,  0.00000000f, },
 };
 
 #endif/*__DSP_IIR_CONFIG_H__*/

firmware/baseband/proc_am_audio.cpp

@@ -21,39 +21,77 @@
 
 #include "proc_am_audio.hpp"
 
-#include <cstdint>
+// 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;
+
+	constexpr size_t decim_0_input_fs = baseband_fs;
+	constexpr size_t decim_0_decimation_factor = 8;
+	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 = 8;
+	constexpr size_t decim_1_output_fs = decim_1_input_fs / decim_1_decimation_factor;
+
+	constexpr size_t channel_filter_input_fs = decim_1_output_fs;
+	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;
+
+	channel_spectrum.set_decimation_factor(std::floor((channel_filter_output_fs / 2) / ((channel_filter_pass_f + channel_filter_stop_f) / 2)));
+}
 
 void NarrowbandAMAudio::execute(const buffer_c8_t& buffer) {
-	auto decimator_out = decimator.execute(buffer);
+	const buffer_c16_t dst_buffer {
-
+		dst.data(),
-	const buffer_c16_t work_baseband_buffer {
+		dst.size()
-		(complex16_t*)decimator_out.p,
-		sizeof(*decimator_out.p) * decimator_out.count
 	};
 
-	/* 96kHz complex<int16_t>[64]
+	const auto decim_0_out = decim_0.execute(buffer, dst_buffer);
-	 * -> FIR filter, <?kHz (0.???fs) pass, gain 1.0
+	const auto decim_1_out = decim_1.execute(decim_0_out, dst_buffer);
-	 * -> 48kHz int16_t[32] */
+	const auto channel_out = channel_filter.execute(decim_1_out, dst_buffer);
-	auto channel = channel_filter.execute(decimator_out, work_baseband_buffer);
 
 	// TODO: Feed channel_stats post-decimation data?
-	feed_channel_stats(channel);
+	feed_channel_stats(channel_out);
-	channel_spectrum.feed(
+	channel_spectrum.feed(channel_out, channel_filter_pass_f, channel_filter_stop_f);
-		channel,
-		decimator_out.sampling_rate * channel_filter_taps.pass_frequency_normalized,
-		decimator_out.sampling_rate * channel_filter_taps.stop_frequency_normalized
-	);
 
 	const buffer_s16_t work_audio_buffer {
-		(int16_t*)decimator_out.p,
+		(int16_t*)dst.data(),
-		sizeof(*decimator_out.p) * decimator_out.count
+		sizeof(*dst.data()) * dst.size()
 	};
 
-	/* 48kHz complex<int16_t>[32]
+	auto audio = demod.execute(channel_out, work_audio_buffer);
-	 * -> AM demodulation
-	 * -> 48kHz int16_t[32] */
-	auto audio = demod.execute(channel, work_audio_buffer);
 
 	audio_hpf.execute_in_place(audio);
+
 	fill_audio_buffer(audio);
 }

firmware/baseband/proc_am_audio.hpp

@@ -33,22 +33,27 @@
 
 #include "spectrum_collector.hpp"
 
+#include <cstdint>
+#include <array>
+
 class NarrowbandAMAudio : public BasebandProcessor {
 public:
-	NarrowbandAMAudio() {
+	NarrowbandAMAudio();
-		decimator.set_decimation_factor(ChannelDecimator::DecimationFactor::By32);
-		channel_filter.configure(channel_filter_taps.taps, 2);
-	}
 	
 	void execute(const buffer_c8_t& buffer) override;
 
 	void on_update_spectrum() override { channel_spectrum.update(); }
 
 private:
-	ChannelDecimator decimator;
+	std::array<complex16_t, 512> dst;
-	const fir_taps_real<64>& channel_filter_taps = taps_64_lp_031_070_tfilter;
+	dsp::decimate::FIRC8xR16x24FS4Decim8 decim_0;
+	dsp::decimate::FIRC16xR16x32Decim8 decim_1;
 	dsp::decimate::FIRAndDecimateComplex channel_filter;
+	uint32_t channel_filter_pass_f;
+	uint32_t channel_filter_stop_f;
+
 	dsp::demodulate::AM demod;
+
 	IIRBiquadFilter audio_hpf { audio_hpf_config };
 
 	SpectrumCollector channel_spectrum;

firmware/baseband/proc_nfm_audio.cpp

@@ -24,44 +24,163 @@
 #include <cstdint>
 #include <cstddef>
 
+// NBFM 16K0F3E emission type /////////////////////////////////////////////
+
+// IFIR image-reject filter: fs=3072000, pass=8000, stop=344000, decim=8, fout=384000
+static constexpr std::array<int16_t, 24> taps_16k0_decim_0 { {
+	     1,     67,    165,    340,    599,    944,   1361,   1820,
+	  2278,   2684,   2988,   3152,   3152,   2988,   2684,   2278,
+	  1820,   1361,    944,    599,    340,    165,     67,      1,
+} };
+
+// IFIR prototype filter: fs=384000, pass=8000, stop=40000, decim=8, fout=48000
+static constexpr std::array<int16_t, 32> taps_16k0_decim_1 { {
+	   -26,   -125,   -180,   -275,   -342,   -359,   -286,    -90,
+	   250,    733,   1337,   2011,   2688,   3289,   3740,   3982,
+	  3982,   3740,   3289,   2688,   2011,   1337,    733,    250,
+	   -90,   -286,   -359,   -342,   -275,   -180,   -125,    -26,
+} };
+
+// Channel filter: fs=48000, pass=8000, stop=12400, decim=1, fout=48000
+static constexpr std::array<int16_t, 32> taps_16k0_channel { {
+	   -73,   -285,   -376,     -8,    609,    538,   -584,  -1387,
+	  -148,   2173,   1959,  -2146,  -5267,   -297,  12915,  24737,
+	 24737,  12915,   -297,  -5267,  -2146,   1959,   2173,   -148,
+	 -1387,   -584,    538,    609,     -8,   -376,   -285,    -73,
+} };
+
+// NBFM 11K0F3E emission type /////////////////////////////////////////////
+
+// IFIR image-reject filter: fs=3072000, pass=5500, stop=341500, decim=8, fout=384000
+static constexpr std::array<int16_t, 24> taps_11k0_decim_0 { {
+	    38,    102,    220,    406,    668,   1004,   1397,   1822,
+	  2238,   2603,   2875,   3020,   3020,   2875,   2603,   2238,
+	  1822,   1397,   1004,    668,    406,    220,    102,     38,
+} };
+
+// IFIR prototype filter: fs=384000, pass=5500, stop=42500, decim=8, fout=48000
+static constexpr std::array<int16_t, 32> taps_11k0_decim_1 { {
+	   -42,    -87,   -157,   -234,   -298,   -318,   -255,    -75,
+	   246,    713,   1306,   1976,   2656,   3265,   3724,   3971,
+	  3971,   3724,   3265,   2656,   1976,   1306,    713,    246,
+	   -75,   -255,   -318,   -298,   -234,   -157,    -87,    -42,
+} };
+
+// Channel filter: fs=48000, pass=5500, stop=8900, decim=1, fout=48000
+static constexpr std::array<int16_t, 32> taps_11k0_channel { {
+	   -68,   -345,   -675,   -867,   -582,    247,   1222,   1562,
+	   634,  -1379,  -3219,  -3068,    310,   6510,  13331,  17795,
+	 17795,  13331,   6510,    310,  -3068,  -3219,  -1379,    634,
+	  1562,   1222,    247,   -582,   -867,   -675,   -345,    -68,
+} };
+
+/// NBFM 8K50F3E emission type ////////////////////////////////////////////
+
+// IFIR image-reject filter: fs=3072000, pass=4250, stop=340250, decim=8, fout=384000
+static constexpr std::array<int16_t, 24> taps_4k25_decim_0 { {
+	    38,    103,    222,    409,    671,   1006,   1399,   1821,
+	  2236,   2599,   2868,   3012,   3012,   2868,   2599,   2236,
+	  1821,   1399,   1006,    671,    409,    222,    103,     38,
+} };
+
+// IFIR prototype filter: fs=384000, pass=4250, stop=43750, decim=8, fout=48000
+static constexpr std::array<int16_t, 32> taps_4k25_decim_1 { {
+	   -33,    -74,   -139,   -214,   -280,   -306,   -254,    -87,
+	   222,    682,   1274,   1951,   2644,   3268,   3741,   3996,
+	  3996,   3741,   3268,   2644,   1951,   1274,    682,    222,
+	   -87,   -254,   -306,   -280,   -214,   -139,    -74,    -33,
+} };
+
+// Channel filter: fs=48000, pass=4250, stop=7900, decim=1, fout=48000
+static constexpr std::array<int16_t, 32> taps_4k25_channel { {
+	   -58,    -14,    153,    484,    871,   1063,    770,   -141,
+	 -1440,  -2488,  -2435,   -614,   3035,   7771,  12226,  14927,
+	 14927,  12226,   7771,   3035,   -614,  -2435,  -2488,  -1440,
+	  -141,    770,   1063,    871,    484,    153,    -14,    -58,
+} };
+
+NarrowbandFMAudio::NarrowbandFMAudio() {
+	set_mode(Mode::Deviation2K5Narrow);
+}
+
+void NarrowbandFMAudio::set_mode(const Mode mode) {
+	constexpr size_t baseband_fs = 3072000;
+
+	constexpr size_t decim_0_input_fs = baseband_fs;
+	constexpr size_t decim_0_decimation_factor = 8;
+	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 = 8;
+	constexpr size_t decim_1_output_fs = decim_1_input_fs / decim_1_decimation_factor;
+
+	constexpr size_t channel_filter_input_fs = decim_1_output_fs;
+	constexpr size_t channel_filter_decimation_factor = 1;
+	constexpr size_t channel_filter_output_fs = channel_filter_input_fs / channel_filter_decimation_factor;
+
+	constexpr size_t demod_input_fs = channel_filter_output_fs;
+
+	switch(mode) {
+	default:
+	case Mode::Deviation5K:
+		decim_0.configure(taps_16k0_decim_0, 33554432);
+		decim_1.configure(taps_16k0_decim_1, 131072);
+		channel_filter.configure(taps_16k0_channel, channel_filter_decimation_factor);
+		demod.configure(demod_input_fs, 5000);
+		channel_filter_pass_f =  8000;
+		channel_filter_stop_f = 12400;
+		break;
+
+	case Mode::Deviation2K5Wide:
+		decim_0.configure(taps_11k0_decim_0, 33554432);
+		decim_1.configure(taps_11k0_decim_1, 131072);
+		channel_filter.configure(taps_11k0_channel, channel_filter_decimation_factor);
+		demod.configure(demod_input_fs, 2500);
+		channel_filter_pass_f = 5500;
+		channel_filter_stop_f = 8900;
+		break;
+
+	case Mode::Deviation2K5Narrow:
+		decim_0.configure(taps_4k25_decim_0, 33554432);
+		decim_1.configure(taps_4k25_decim_1, 131072);
+		channel_filter.configure(taps_4k25_channel, channel_filter_decimation_factor);
+		demod.configure(demod_input_fs, 2500);
+		channel_filter_pass_f = 4250;
+		channel_filter_stop_f = 7900;
+		break;
+	}
+
+	channel_spectrum.set_decimation_factor(std::floor((channel_filter_output_fs / 2) / ((channel_filter_pass_f + channel_filter_stop_f) / 2)));
+}
+
 void NarrowbandFMAudio::execute(const buffer_c8_t& buffer) {
-	/* Called every 2048/3072000 second -- 1500Hz. */
+	const buffer_c16_t dst_buffer {
-
+		dst.data(),
-	auto decimator_out = decimator.execute(buffer);
+		dst.size()
-
-	const buffer_c16_t work_baseband_buffer {
-		(complex16_t*)decimator_out.p,
-		sizeof(*decimator_out.p) * decimator_out.count
 	};
 
-	/* 96kHz complex<int16_t>[64]
+	const auto decim_0_out = decim_0.execute(buffer, dst_buffer);
-	 * -> FIR filter, <6kHz (0.063fs) pass, gain 1.0
+	const auto decim_1_out = decim_1.execute(decim_0_out, dst_buffer);
-	 * -> 48kHz int16_t[32] */
+	const auto channel_out = channel_filter.execute(decim_1_out, dst_buffer);
-	auto channel = channel_filter.execute(decimator_out, work_baseband_buffer);
 
-	// TODO: Feed channel_stats post-decimation data?
+	feed_channel_stats(channel_out);
-	feed_channel_stats(channel);
+	channel_spectrum.feed(channel_out, channel_filter_pass_f, channel_filter_stop_f);
-	channel_spectrum.feed(
-		channel,
-		decimator_out.sampling_rate * channel_filter_taps.pass_frequency_normalized,
-		decimator_out.sampling_rate * channel_filter_taps.stop_frequency_normalized
-	);
 
 	const buffer_s16_t work_audio_buffer {
-		(int16_t*)decimator_out.p,
+		(int16_t*)dst.data(),
-		sizeof(*decimator_out.p) * decimator_out.count
+		sizeof(*dst.data()) * dst.size()
 	};
 
-	/* 48kHz complex<int16_t>[32]
+	auto audio = demod.execute(channel_out, work_audio_buffer);
-	 * -> FM demodulation
-	 * -> 48kHz int16_t[32] */
-	auto audio = demod.execute(channel, work_audio_buffer);
 
 	static uint64_t audio_present_history = 0;
 	const auto audio_present_now = squelch.execute(audio);
 	audio_present_history = (audio_present_history << 1) | (audio_present_now ? 1 : 0);
 	const bool audio_present = (audio_present_history != 0);
 
+	audio_hpf.execute_in_place(audio);
+	audio_deemph.execute_in_place(audio);
+
 	if( !audio_present ) {
 		// Zero audio buffer.
 		for(size_t i=0; i<audio.count; i++) {
@@ -69,6 +188,5 @@ void NarrowbandFMAudio::execute(const buffer_c8_t& buffer) {
 		}
 	}
 
-	audio_hpf.execute_in_place(audio);
 	fill_audio_buffer(audio);
 }

firmware/baseband/proc_nfm_audio.hpp

@@ -36,22 +36,33 @@
 
 class NarrowbandFMAudio : public BasebandProcessor {
 public:
-	NarrowbandFMAudio() {
+	enum class Mode {
-		decimator.set_decimation_factor(ChannelDecimator::DecimationFactor::By32);
+		Deviation5K = 0,
-		channel_filter.configure(channel_filter_taps.taps, 2);
+		Deviation2K5Wide = 1,
-	}
+		Deviation2K5Narrow = 2,
+	};
+
+	NarrowbandFMAudio();
+
+	void set_mode(const Mode mode);
 
 	void execute(const buffer_c8_t& buffer) override;
 
 	void on_update_spectrum() override { channel_spectrum.update(); }
 
 private:
-	ChannelDecimator decimator;
+	std::array<complex16_t, 512> dst;
-	const fir_taps_real<64>& channel_filter_taps = taps_64_lp_042_078_tfilter;
+	dsp::decimate::FIRC8xR16x24FS4Decim8 decim_0;
+	dsp::decimate::FIRC16xR16x32Decim8 decim_1;
+
 	dsp::decimate::FIRAndDecimateComplex channel_filter;
-	dsp::demodulate::FM demod { 48000, 7500 };
+	uint32_t channel_filter_pass_f = 0;
+	uint32_t channel_filter_stop_f = 0;
+
+	dsp::demodulate::FM demod;
 
 	IIRBiquadFilter audio_hpf { audio_hpf_config };
+	IIRBiquadFilter audio_deemph { audio_deemph_300_6_config };
 	FMSquelch squelch;
 
 	SpectrumCollector channel_spectrum;

firmware/baseband/proc_wideband_spectrum.hpp

@@ -38,7 +38,7 @@ public:
 private:
 	size_t sample_count = 0;
 
-	SpectrumCollector channel_spectrum { 1 };
+	SpectrumCollector channel_spectrum;
 
 	std::array<complex16_t, 256> spectrum;
 };

firmware/baseband/spectrum_collector.cpp

@@ -29,6 +29,12 @@
 
 #include <algorithm>
 
+void SpectrumCollector::set_decimation_factor(
+	const size_t decimation_factor
+) {
+	channel_spectrum_decimator.set_factor(decimation_factor);
+}
+
 /* TODO: Refactor to register task with idle thread?
  * It's sad that the idle thread has to call all the way back here just to
  * perform the deferred task on the buffer of data we prepared.

firmware/baseband/spectrum_collector.hpp

@@ -33,11 +33,12 @@
 class SpectrumCollector {
 public:
 	constexpr SpectrumCollector(
-		const size_t decimation_factor = 4
+	) : channel_spectrum_decimator { 1 }
-	) : channel_spectrum_decimator { decimation_factor }
 	{
 	}
 
+	void set_decimation_factor(const size_t decimation_factor);
+
 	void feed(
 		const buffer_c16_t& channel,
 		const uint32_t filter_pass_frequency,