Increase FFT size and frequency resolution
This commit is contained in:
Thomas Kolb
parent
75611bb4e1
commit
523a7bdaf1
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@ -33,7 +33,7 @@ void complex_to_absolute(value_type *re, value_type *im, value_type *result) {
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for(i = 0; i < DATALEN; i++)
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{
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result[i] = sqrt( re[i]*re[i] + im[i]*im[i] );
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result[i] = sqrtf( re[i]*re[i] + im[i]*im[i] );
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}
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}
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@ -135,7 +135,7 @@ value_type get_energy_in_band(value_type *fft, uint32_t minFreq, uint32_t maxFre
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return energy;
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}
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value_type get_energy_density_in_band(value_type *fft, uint32_t minFreq, uint32_t maxFreq) {
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value_type get_spectral_density_in_band(value_type *fft, uint32_t minFreq, uint32_t maxFreq) {
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int firstBlock = minFreq * BLOCK_LEN / SAMPLE_RATE;
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int lastBlock = maxFreq * BLOCK_LEN / SAMPLE_RATE;
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int i;
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@ -149,7 +149,7 @@ value_type get_energy_density_in_band(value_type *fft, uint32_t minFreq, uint32_
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energy /= (lastBlock - firstBlock);
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}
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energy *= (float)BLOCK_LEN / (float)SAMPLE_RATE; // normalze to Hz
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energy *= sqrtf((float)BLOCK_LEN / (float)SAMPLE_RATE); // normalze to sqrt(Hz)
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return energy;
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}
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@ -11,6 +11,8 @@ void apply_hanning(value_type *dftinput);
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void fft_transform(value_type *samples, value_type *resultRe, value_type *resultIm);
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uint32_t find_loudest_frequency(value_type *absFFT);
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value_type get_energy_in_band(value_type *fft, uint32_t minFreq, uint32_t maxFreq);
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value_type get_energy_density_in_band(value_type *fft, uint32_t minFreq, uint32_t maxFreq);
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// calculate the spectral density in V/sqrt(Hz)
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value_type get_spectral_density_in_band(value_type *fft, uint32_t minFreq, uint32_t maxFreq);
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#endif // FFT_H
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@ -2,7 +2,7 @@
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#define CONFIG_H
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// FFT transformation parameters
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#define FFT_EXPONENT 9 // ATTENTION: when you change this, run gen_lut.py with this value as argument
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#define FFT_EXPONENT 11 // ATTENTION: when you change this, run gen_lut.py with this value as argument
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#define BLOCK_LEN (1 << FFT_EXPONENT) // 2^FFT_EXPONENT
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#define SAMPLE_RATE 48000
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#define DATALEN (BLOCK_LEN / 2)
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134
src/main.cpp
134
src/main.cpp
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@ -19,6 +19,7 @@ extern "C" {
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}
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#define ENDLESS_LOOP() while(true) { delay(100); }
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#define ARRAY_SIZE(x) ((size_t)(sizeof(x) / sizeof(x[0])))
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#define OUTPUT_INTERVAL 10000 // milliseconds
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@ -30,8 +31,12 @@ static bool wiFiConnectedToStation;
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static AutoAnalog recorder;
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// too large for the stack
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static value_type timedomain[SAMPLES_PER_BLOCK];
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static value_type fft_re[BLOCK_LEN], fft_im[BLOCK_LEN], fft_abs[BLOCK_LEN];
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static size_t timedomain_write_offset;
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static value_type timedomain[BLOCK_LEN];
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static value_type fft_re[BLOCK_LEN], fft_im[BLOCK_LEN];
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const static uint16_t band_edges[] = {0, 40, 80, 120, 200, 400, 800, 1600, 3200, 6400, 12800, 20000};
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static value_type total_energy[ARRAY_SIZE(band_edges) - 1];
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void wifi_setup(void)
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{
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@ -85,7 +90,6 @@ void wifi_setup(void)
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} else {
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digitalWrite(LED_BUILTIN, true); // LED OFF (active low)
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}
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}
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void setup()
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@ -121,6 +125,9 @@ void setup()
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init_fft();
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timedomain_write_offset = 0;
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memset(total_energy, 0, sizeof(total_energy));
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// start sampling
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recorder.enableAdcChannel(6);
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recorder.begin(true, false);
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@ -135,78 +142,78 @@ void loop() {
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static uint32_t last_output_time = 0;
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static uint32_t nsamples = 0;
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static value_type total_energy_0_to_300_hz = 0.0f;
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static value_type total_energy_300_to_3500_hz = 0.0f;
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static value_type total_energy_3500_to_8000_hz = 0.0f;
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static value_type total_energy_8000_to_20000_hz = 0.0f;
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wiFiMulti.run(); // maintain the WiFi connection
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recorder.getADC(SAMPLES_PER_BLOCK);
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// convert to Volt (float)
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for(size_t i = 0; i < SAMPLES_PER_BLOCK; i++) {
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timedomain[i] = (value_type)recorder.adcBuffer16[i] / 4096.0f * 3.30f;
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timedomain[i + timedomain_write_offset] = (value_type)recorder.adcBuffer16[i] / 4096.0f * 3.30f;
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}
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timedomain_write_offset += SAMPLES_PER_BLOCK;
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// calculate average value
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value_type avg = 0;
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for(size_t i = 0; i < SAMPLES_PER_BLOCK; i++) {
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avg += timedomain[i];
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if(timedomain_write_offset >= ARRAY_SIZE(timedomain)) {
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timedomain_write_offset = 0;
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// calculate average value
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value_type avg = 0;
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for(size_t i = 0; i < ARRAY_SIZE(timedomain); i++) {
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avg += timedomain[i];
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}
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avg /= ARRAY_SIZE(timedomain);
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// and remove it from the data
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for(size_t i = 0; i < ARRAY_SIZE(timedomain); i++) {
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timedomain[i] -= avg;
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}
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apply_hanning(timedomain);
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fft_transform(timedomain, fft_re, fft_im);
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// HACK: reuse now unused timedomain memory for absolute FFT
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value_type *fft_abs = timedomain;
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complex_to_absolute(fft_re, fft_im, fft_abs);
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// accumulate energy in bands
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for(size_t i = 0; i < ARRAY_SIZE(total_energy); i++) {
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total_energy[i] += get_spectral_density_in_band(fft_abs, band_edges[i], band_edges[i+1]);
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}
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// force restart sampling due to calculation delay (might cause glitches)
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recorder.getADC(SAMPLES_PER_BLOCK);
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timedomain_write_offset = 0;
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nsamples++;
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}
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avg /= SAMPLES_PER_BLOCK;
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// and remove it from the data
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for(size_t i = 0; i < SAMPLES_PER_BLOCK; i++) {
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timedomain[i] -= avg;
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}
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apply_hanning(timedomain);
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fft_transform(timedomain, fft_re, fft_im);
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complex_to_absolute(fft_re, fft_im, fft_abs);
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value_type energy_0_to_300_hz = get_energy_density_in_band(fft_abs, 0, 300);
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value_type energy_300_to_3500_hz = get_energy_density_in_band(fft_abs, 300, 3500);
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value_type energy_3500_to_8000_hz = get_energy_density_in_band(fft_abs, 3500, 8000);
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value_type energy_8000_to_20000_hz = get_energy_density_in_band(fft_abs, 8000, 20000);
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total_energy_0_to_300_hz += energy_0_to_300_hz;
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total_energy_300_to_3500_hz += energy_300_to_3500_hz;
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total_energy_3500_to_8000_hz += energy_3500_to_8000_hz;
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total_energy_8000_to_20000_hz += energy_8000_to_20000_hz;
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nsamples++;
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uint32_t now = millis();
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if(now - last_output_time > OUTPUT_INTERVAL) {
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total_energy_0_to_300_hz /= nsamples;
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total_energy_300_to_3500_hz /= nsamples;
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total_energy_3500_to_8000_hz /= nsamples;
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total_energy_8000_to_20000_hz /= nsamples;
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String json_string = "{";
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// calculate dBV
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value_type dBV_per_Hz_0_to_300_hz = 20*log10(total_energy_0_to_300_hz);
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value_type dBV_per_Hz_300_to_3500_hz = 20*log10(total_energy_300_to_3500_hz);
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value_type dBV_per_Hz_3500_to_8000_hz = 20*log10(total_energy_3500_to_8000_hz);
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value_type dBV_per_Hz_8000_to_20000_hz = 20*log10(total_energy_8000_to_20000_hz);
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Serial.print("Samples taken: ");
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Serial.println(nsamples);
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Serial.print(" 0 - 300 Hz [dBV/Hz]: ");
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Serial.println(dBV_per_Hz_0_to_300_hz);
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Serial.print(" 300 - 3500 Hz [dBV/Hz]: ");
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Serial.println(dBV_per_Hz_300_to_3500_hz);
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Serial.print(" 3500 - 8000 Hz [dBV/Hz]: ");
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Serial.println(dBV_per_Hz_3500_to_8000_hz);
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Serial.print(" 8000 - 20000 Hz [dBV/Hz]: ");
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Serial.println(dBV_per_Hz_8000_to_20000_hz);
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for(size_t i = 0; i < ARRAY_SIZE(total_energy); i++) {
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value_type dBV_per_sqrt_Hz = 20*log10f(total_energy[i] / nsamples);
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Serial.println();
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uint16_t fstart = band_edges[i];
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uint16_t fend = band_edges[i+1];
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// encode the data into JSON
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String json_string = "{"
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"\"0_to_300_hz\":" + String(dBV_per_Hz_0_to_300_hz, 2) + ","
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"\"300_to_3500_hz\":" + String(dBV_per_Hz_300_to_3500_hz, 2) + ","
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"\"3500_to_8000_hz\":" + String(dBV_per_Hz_3500_to_8000_hz, 2) + ","
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"\"8000_to_20000_hz\":" + String(dBV_per_Hz_8000_to_20000_hz, 2) + "}";
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Serial.printf("%5d - %5d Hz: %.2f dBV/√Hz / %f Vrms\r\n", fstart, fend, dBV_per_sqrt_Hz, total_energy[i]);
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if(i != 0) {
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json_string += ", ";
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}
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// encode the data into JSON
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char indexstr[5];
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snprintf(indexstr, sizeof(indexstr), "%03zu_", i);
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json_string += "\"" + String(indexstr) + String(fstart) + "_to_" + String(fend) + "_hz\": " + String(dBV_per_sqrt_Hz, 2);
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}
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json_string += "}";
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// send the data to graphite
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HTTPClient client;
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@ -227,12 +234,13 @@ void loop() {
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}
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// reset accumulation
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total_energy_0_to_300_hz = 0.0f;
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total_energy_300_to_3500_hz = 0.0f;
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total_energy_3500_to_8000_hz = 0.0f;
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total_energy_8000_to_20000_hz = 0.0f;
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memset(total_energy, 0, sizeof(total_energy));
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nsamples = 0;
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// force restart sampling due to transmit delay (causes glitches)
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recorder.getADC(SAMPLES_PER_BLOCK);
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timedomain_write_offset = 0;
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last_output_time = now;
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}
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