Extend REC low bit rate bandwith options in Capture App till 75khz (#1380)

* working_x32_Capture_till_75Khz

* format issues

* apply better accurate comments

* auto format issues

firmware/application/freqman_db.cpp

@@ -78,6 +78,7 @@ options_t freqman_bandwidths[4] = {
         {"16k", 16000},
         {"25k", 25000},
         {"50k", 50000},
+        {"75k", 75000},
         {"100k", 100000},
         {"150k", 150000},
         {"250k", 250000},

firmware/application/ui/ui_spectrum.cpp

@@ -383,7 +383,7 @@ void WaterfallView::on_audio_spectrum() {
 // TODO: Comments below refer to a fixed oversample rate (8x), cleanup.
 uint32_t filter_bandwidth_for_sampling_rate(int32_t sampling_rate) {
     switch (sampling_rate) {   // Use the var fs (sampling_rate) to set up BPF aprox < fs_max / 2 by Nyquist theorem.
-        case 0 ... 3'000'000:  // BW Captured range (0 <= 250kHz max)  fs = 8 x 250 kHz., 16 x 150 khz, 32 x 75 khz, , 64 x 40 khz
+        case 0 ... 3'500'000:  // BW Captured range (0 <= 250kHz max)  fs = 8x250 kHz =2000., 16x150 khz =2400, 32x100 khz =3200, (32x75k = 2400), (future 64x40 khz =2400)
             return 1'750'000;  // Minimum BPF MAX2837 for all those lower BW options.
 
         case 4'000'000 ... 6'000'000:  // BW capture range (500k...750kHz max)  fs_max = 8 x 750kHz = 6Mhz

firmware/application/ui_record_view.cpp

@@ -145,11 +145,11 @@ OversampleRate RecordView::get_oversample_rate(uint32_t sample_rate) {
 
     auto rate = ::get_oversample_rate(sample_rate);
 
-    // Currently proc_capture only supports x8 and x16 for decimation.
+    // Currently proc_capture only supports x8, x16, x32 for decimation.
-    if (rate < OversampleRate::x8)
+    if (rate < OversampleRate::x8)  // clipping while x4 is not implemented yet.
         rate = OversampleRate::x8;
-    else if (rate > OversampleRate::x16)
+    else if (rate > OversampleRate::x32)  // clipping while x64 is not implemented yet .
-        rate = OversampleRate::x16;
+        rate = OversampleRate::x32;
 
     return rate;
 }

firmware/baseband/proc_capture.cpp

@@ -31,7 +31,8 @@ CaptureProcessor::CaptureProcessor() {
     decim_0_8.configure(taps_200k_decim_0.taps, 33554432);           // to be used with decim1 (/2), then total two stages decim (/16)
     decim_0_8_180k.configure(taps_180k_wfm_decim_0.taps, 33554432);  // to be used alone - no additional decim1 (/2), then total single stage decim (/8)
 
-    decim_1.configure(taps_200k_decim_1.taps, 131072);
+    decim_1_2.configure(taps_200k_decim_1.taps, 131072);
+    decim_1_8.configure(taps_16k0_decim_1.taps, 131072);  // tentative decim1 /8  and taps, pending to be optimized.
 
     channel_spectrum.set_decimation_factor(1);
     baseband_thread.start();
@@ -39,11 +40,16 @@ CaptureProcessor::CaptureProcessor() {
 
 void CaptureProcessor::execute(const buffer_c8_t& buffer) {
     /* 2.4576MHz, 2048 samples */
-    const auto decim_0_out = decim_0_execute(buffer, dst_buffer);  // selectable 3 possible decim_0, (/4.  /8 200k soft transition filter , /8 180k sharp )
+    const auto decim_0_out = decim_0_execute(buffer, dst_buffer);       // selectable 3 possible decim_0, (/4.  /8 200k soft filter , /8 180k sharp )
+    const auto decim_1_out = decim_1_execute(decim_0_out, dst_buffer);  // selectable 3 possible decim_1, (/8.  /2 200k or bypassed /1  )
 
+    /* this code was valid when we had only 2 decim1 cases.
     const auto decim_1_out = baseband_fs < 4800'000
-                                 ? decim_1.execute(decim_0_out, dst_buffer)  // < 600khz double decim. stage , means 500khz and lower bit rates.
+                                  ? decim_1_2.execute(decim_0_out, dst_buffer)  // < 600khz double decim. stage , means 500khz and lower bit rates.
-                                 : decim_0_out;                              // >= 600khz single decim. stage , means 600khz and upper bit rates.
+                                 // ? decim_1_8.execute(decim_0_out, dst_buffer)  // < 600khz double decim. stage , means 500khz and lower bit rates.
+                                  : decim_0_out;                              // >= 600khz single decim. stage , means 600khz and upper bit rates.
+
+     } */
 
     const auto& decimator_out = decim_1_out;
     const auto& channel = decimator_out;
@@ -91,13 +97,44 @@ void CaptureProcessor::sample_rate_config(const SampleRateConfigMessage& message
 
     baseband_thread.set_sampling_rate(baseband_fs);
 
+    // Current fw , we are using only  2 decim_0 modes,  /4 , /8
     auto decim_0_factor = oversample_rate == OversampleRate::x8
                               ? decim_0_4.decimation_factor
                               : decim_0_8.decimation_factor;
-    size_t decim_0_output_fs = baseband_fs / decim_0_factor;
 
+    size_t decim_0_output_fs = baseband_fs / decim_0_factor;
     size_t decim_1_input_fs = decim_0_output_fs;
-    size_t decim_1_output_fs = decim_1_input_fs / decim_1.decimation_factor;
+
+    size_t decim_1_factor;
+    switch (oversample_rate) {  // we are using 3 decim_1 modes,  /1 , /2 ,  /8
+        case OversampleRate::x8:
+            if (baseband_fs < 4800'000) {
+                decim_1_factor = decim_1_2.decimation_factor;  // /8 = /4x2
+            } else {
+                decim_1_factor = 2 * 1;  // 600khz and onwards, single decim /8 = /8x1 (we applied additional *2 correction to speed up waterfall, no effect to scale spectrum)
+            }
+            break;
+
+        case OversampleRate::x16:
+            decim_1_factor = 2 * decim_1_2.decimation_factor;  // /16 = /8x2 (we applied additional *2 correction to increase waterfall spped >=600k and smooth & avoid abnormal motion >1M5 )
+            break;
+
+        case OversampleRate::x32:
+            decim_1_factor = 2 * decim_1_8.decimation_factor;  // /x32 = /4x8 (we applied additional *2 correction to speed up waterfall, no effect to scale spectrum)
+            break;
+
+        default:
+            decim_1_factor = 2;  // just default initial value to remove compile warning.
+            break;
+    }
+
+    /*
+    auto decim_1_factor = oversample_rate == OversampleRate::x32    // that was ok,  when we had only 2 oversampling x8 , x16
+                              ? decim_1_8.decimation_factor
+                              : decim_1_2.decimation_factor;
+
+    */
+    size_t decim_1_output_fs = decim_1_input_fs / decim_1_factor;
 
     channel_filter_low_f = taps_200k_decim_1.low_frequency_normalized * decim_1_input_fs;
     channel_filter_high_f = taps_200k_decim_1.high_frequency_normalized * decim_1_input_fs;
@@ -117,15 +154,39 @@ void CaptureProcessor::capture_config(const CaptureConfigMessage& message) {
 
 buffer_c16_t CaptureProcessor::decim_0_execute(const buffer_c8_t& src, const buffer_c16_t& dst) {
     switch (oversample_rate) {
-        case OversampleRate::x8:                     // we can get /8 by two means , decim0 (:4) + decim1 (:2) .  or just decim0 (;8)
+        case OversampleRate::x8:                     // we can get /8 by two means , decim0 (/4) + decim1 (/2) .  or just decim0 (/8)
             if (baseband_fs < 4800'000) {            // 600khz (600k x 8)
-                return decim_0_4.execute(src, dst);  // decim_0  /4 with double decim stage
+                return decim_0_4.execute(src, dst);  // decim_0 , /4 with double decim stage
             } else {
                 return decim_0_8_180k.execute(src, dst);  // decim_0  /8 with single decim stage
             }
 
         case OversampleRate::x16:
-            return decim_0_8.execute(src, dst);
+            return decim_0_8.execute(src, dst);  // decim_0 , /8 with double decim stage
+
+        case OversampleRate::x32:
+            return decim_0_4.execute(src, dst);  // decim_0 , /4 with double decim stage
+
+        default:
+            chDbgPanic("Unhandled OversampleRate");
+            return {};
+    }
+}
+
+buffer_c16_t CaptureProcessor::decim_1_execute(const buffer_c16_t& src, const buffer_c16_t& dst) {
+    switch (oversample_rate) {
+        case OversampleRate::x8:           // we can get /8 by two means , decim0 (/4) + decim1 (/2) .  or just decim0 (/8)
+            if (baseband_fs < 4800'000) {  // 600khz (600k x 8)
+                return decim_1_2.execute(src, dst);
+            } else {
+                return src;
+            }
+
+        case OversampleRate::x16:
+            return decim_1_2.execute(src, dst);  // total decim /16 = /8x2, applied to 150khz
+
+        case OversampleRate::x32:
+            return decim_1_8.execute(src, dst);  // total decim /32 = /4x8, appled to <= 100khz , 75k with margin ,(50k, 25k, 12k5 now also)  ...
 
         default:
             chDbgPanic("Unhandled OversampleRate");

firmware/baseband/proc_capture.hpp

@@ -57,7 +57,8 @@ class CaptureProcessor : public BasebandProcessor {
     dsp::decimate::FIRC8xR16x24FS4Decim4 decim_0_4{};
     dsp::decimate::FIRC8xR16x24FS4Decim8 decim_0_8{};
     dsp::decimate::FIRC8xR16x24FS4Decim8 decim_0_8_180k{};
-    dsp::decimate::FIRC16xR16x16Decim2 decim_1{};
+    dsp::decimate::FIRC16xR16x16Decim2 decim_1_2{};
+    dsp::decimate::FIRC16xR16x32Decim8 decim_1_8{};
 
     int32_t channel_filter_low_f = 0;
     int32_t channel_filter_high_f = 0;
@@ -80,6 +81,9 @@ class CaptureProcessor : public BasebandProcessor {
 
     /* Dispatch to the correct decim_0 based on oversample rate. */
     buffer_c16_t decim_0_execute(const buffer_c8_t& src, const buffer_c16_t& dst);
+
+    /* Dispatch to the correct decim_1 based on oversample rate. */
+    buffer_c16_t decim_1_execute(const buffer_c16_t& src, const buffer_c16_t& dst);
 };
 
 #endif /*__PROC_CAPTURE_HPP__*/

firmware/common/oversample.hpp

@@ -40,17 +40,29 @@
  * The baseband needs to know how to correctly decimate (or interpolate) so
  * the set of allowed scalars is fixed (See OversampleRate enum).
  * In testing, a minimum rate of 400kHz seems to the functional minimum.
+ *
+ * There are several different concepts or terms related to Capture and Replay,
+ * (1) oversampling (x8, x16 ,...) / decimation (/8, /16...)
+ * In Capture App , when ADC can not handle directly a requiered low sample rates ,
+ * we need to apply oversampling (x8. x16 ex) , getting more real samples than needed) by "x_number" ,
+ * and later to write it to SD card with the proper needed real sample rate , we apply Decimation  , "/ number" .
+ *
+ * (2) up-sampling or re-escale or interpolation. (x8, x16, ...)
+ * In Replay-list App, when we got too low bit rate data for Hackrf ,
+ * we need to upsampling or interpolate or resampling to increase those low bit rates
+ * to a proper sample rate higher than the min. to be able to be transmitted by Hackrf.
  */
 
 /* Gets the oversample rate for a given sample rate.
  * The oversample rate is used to increase the sample rate to improve SNR and quality.
  * This is also used as the interpolation rate when replaying captures. */
 inline OversampleRate get_oversample_rate(uint32_t sample_rate) {
-    if (sample_rate < 50'000) return OversampleRate::x128;  // 25kk..12k5, prepared for future, OVS ok, but decim. :128 still not implemented.
+    if (sample_rate < 50'000) return OversampleRate::x128;  // 25k..12k5, prepared for future, OVS ok, but decim. x128 still not implemented.
-    if (sample_rate < 100'000) return OversampleRate::x64;  // 50k, prepared for future, OVS ok, but decim. :64 still not implemented.
+    if (sample_rate < 100'000) return OversampleRate::x64;  // 50k, prepared for future, OVS ok, but decim. x64 still not implemented.
-    if (sample_rate < 250'000) return OversampleRate::x16;  // Now tentatively applied to 150k..100k - but as soon as we got decim :32, (150k x16, and 100k x32)
+    if (sample_rate < 150'000) return OversampleRate::x32;  // 100k needs x32
+    if (sample_rate < 250'000) return OversampleRate::x16;  // 150k needs x16
 
-    return OversampleRate::x8;  // 250k .. 1Mhz, that decim :8 , is already applied.(OVS and decim OK)
+    return OversampleRate::x8;  // 250k .. 1Mhz, that decim x8 , is already applied.(OVerSampling and decim OK)
 }
 
 /* Gets the actual sample rate for a given sample rate.