micd: apply A-weighting to the sound pressure level

selfdrive/ui/soundd/sound.cc

@@ -48,7 +48,7 @@ void Sound::update() {
 
   // scale volume with speed
   if (sm.updated("microphone")) {
-    float volume = util::map_val(sm["microphone"].getMicrophone().getFilteredSoundPressureDb(), 58.f, 77.f, 0.f, 1.f);
+    float volume = util::map_val(sm["microphone"].getMicrophone().getFilteredSoundPressureWeightedDb(), 30.f, 55.f, 0.f, 1.f);
     volume = QAudio::convertVolume(volume, QAudio::LogarithmicVolumeScale, QAudio::LinearVolumeScale);
     Hardware::set_volume(volume);
   }

system/micd.py

@@ -10,7 +10,35 @@
 
 RATE = 10
 DT_MIC = 1. / RATE
-REFERENCE_SPL = 2 * 10 ** -5  # newtons/m^2
+REFERENCE_SPL = 2e-5  # newtons/m^2
+SAMPLE_RATE = 44100
+
+
+def calculate_spl(measurements):
+  # https://www.engineeringtoolbox.com/sound-pressure-d_711.html
+  sound_pressure = np.sqrt(np.mean(measurements ** 2))  # RMS of amplitudes
+  if sound_pressure > 0:
+    sound_pressure_level = 20 * np.log10(sound_pressure / REFERENCE_SPL)  # dB
+  else:
+    sound_pressure_level = 0
+  return sound_pressure, sound_pressure_level
+
+
+def apply_a_weighting(measurements: np.ndarray) -> np.ndarray:
+  # Generate a Hanning window of the same length as the audio measurements
+  hanning_window = np.hanning(len(measurements))
+  measurements_windowed = measurements * hanning_window
+
+  # Calculate the frequency axis for the signal
+  freqs = np.fft.fftfreq(measurements_windowed.size, d=1 / SAMPLE_RATE)
+
+  # Calculate the A-weighting filter
+  # https://en.wikipedia.org/wiki/A-weighting
+  A = 12194 ** 2 * freqs ** 4 / ((freqs ** 2 + 20.6 ** 2) * (freqs ** 2 + 12194 ** 2) * np.sqrt((freqs ** 2 + 107.7 ** 2) * (freqs ** 2 + 737.9 ** 2)))
+  A /= np.max(A)  # Normalize the filter
+
+  # Apply the A-weighting filter to the signal
+  return np.abs(np.fft.ifft(np.fft.fft(measurements_windowed) * A))
 
 
 class Mic:
@@ -19,27 +47,35 @@ def __init__(self, pm):
     self.rk = Ratekeeper(RATE)
 
     self.measurements = np.empty(0)
-    self.spl_filter = FirstOrderFilter(0, 4, DT_MIC, initialized=False)
+    self.spl_filter_weighted = FirstOrderFilter(0, 2.5, DT_MIC, initialized=False)
 
   def update(self):
-    # self.measurements contains amplitudes from -1 to 1 which we use to
-    # calculate an uncalibrated sound pressure level
+    """
+    Using amplitude measurements, calculate an uncalibrated sound pressure and sound pressure level.
+    Then apply A-weighting to the raw amplitudes and run the same calculations again.
+
+    Logged A-weighted equivalents are rough approximations of the human-perceived loudness.
+    """
+
     if len(self.measurements) > 0:
-      # https://www.engineeringtoolbox.com/sound-pressure-d_711.html
-      sound_pressure = np.sqrt(np.mean(self.measurements ** 2))  # RMS of amplitudes
-      sound_pressure_level = 20 * np.log10(sound_pressure / REFERENCE_SPL) if sound_pressure > 0 else 0  # dB
+      sound_pressure, _ = calculate_spl(self.measurements)
+      measurements_weighted = apply_a_weighting(self.measurements)
+      sound_pressure_weighted, sound_pressure_level_weighted = calculate_spl(measurements_weighted)
       if not HARDWARE.is_sound_playing():
-        self.spl_filter.update(sound_pressure_level)
+        self.spl_filter_weighted.update(sound_pressure_level_weighted)
     else:
       sound_pressure = 0
-      sound_pressure_level = 0
+      sound_pressure_weighted = 0
+      sound_pressure_level_weighted = 0
 
     self.measurements = np.empty(0)
 
     msg = messaging.new_message('microphone')
     msg.microphone.soundPressure = float(sound_pressure)
-    msg.microphone.soundPressureDb = float(sound_pressure_level)
-    msg.microphone.filteredSoundPressureDb = float(self.spl_filter.x)
+    msg.microphone.soundPressureWeighted = float(sound_pressure_weighted)
+
+    msg.microphone.soundPressureWeightedDb = float(sound_pressure_level_weighted)
+    msg.microphone.filteredSoundPressureWeightedDb = float(self.spl_filter_weighted.x)
 
     self.pm.send('microphone', msg)
     self.rk.keep_time()
@@ -51,13 +87,13 @@ def micd_thread(self, device=None):
     if device is None:
       device = "sysdefault"
 
-    with sd.InputStream(device=device, channels=1, samplerate=44100, callback=self.callback) as stream:
+    with sd.InputStream(device=device, channels=1, samplerate=SAMPLE_RATE, callback=self.callback) as stream:
       cloudlog.info(f"micd stream started: {stream.samplerate=} {stream.channels=} {stream.dtype=} {stream.device=}")
       while True:
         self.update()
 
 
-def main(pm=None, sm=None):
+def main(pm=None):
   if pm is None:
     pm = messaging.PubMaster(['microphone'])