1 files changed, 66 insertions, 8 deletions
diff --git a/tools/pdm2pcm.py b/tools/pdm2pcm.py
index f21803a..765c8b6 100644
--- a/tools/pdm2pcm.py
+++ b/tools/pdm2pcm.py
@@ -13,13 +13,68 @@ def load_pdm_file(filename):
     pdm_signal = bit_data
     return pdm_signal
 
-def pdm_to_pcm(pdm_signal, decimation_factor=64):
-    # Design a low-pass filter
-    fir_filter = firwin(numtaps=101, cutoff=0.5/decimation_factor)
-    # Filter the PDM signal
-    filtered = lfilter(fir_filter, [1.0], pdm_signal)
-    # Decimate (downsample)
-    pcm_signal = filtered[::decimation_factor]
+
+def cic_decimate(input_signal, decimation_factor=64, stages=3, delay=1):
+    R = decimation_factor
+    N = stages
+    M = delay
+
+    # Integrator stages
+    integrators = [0] * N
+    integrator_outputs = []
+
+    for sample in input_signal:
+        integrators[0] += sample
+        for i in range(1, N):
+            integrators[i] += integrators[i-1]
+        integrator_outputs.append(integrators[-1])
+
+    # Decimation
+    decimated = integrator_outputs[R-1::R]
+
+    # Comb stages
+    combs = [0] * N
+    comb_outputs = []
+    delays = [[0]*M for _ in range(N)]
+
+    for sample in decimated:
+        diff = sample
+        for i in range(N):
+            delayed = delays[i].pop(0)
+            delays[i].append(diff)
+            diff = diff - delayed
+            combs[i] = diff
+        comb_outputs.append(combs[-1])
+
+    return comb_outputs
+
+
+def pdm_to_pcm(pdm_signal, decimation_factor=64, filter_type='fir', filter_kwargs={}):
+    if filter_type == 'fir':
+        # Design a low-pass filter
+        defaults = dict(numtaps=501, cutoff=0.5/decimation_factor)
+        kwargs = {}
+        kwargs.update(defaults)
+        kwargs.update(filter_kwargs)
+        fir_filter = firwin(**kwargs)
+        # Filter the PDM signal
+        filtered = lfilter(fir_filter, [1.0], pdm_signal)
+        # Decimate (downsample)
+        pcm_signal = filtered[::decimation_factor]
+
+    elif filter_type == 'cic':
+        # Use CIC filter
+        defaults = dict(stages=3, delay=1)
+        kwargs = {}
+        kwargs.update(defaults)
+        kwargs.update(filter_kwargs)
+        # Convert 1-bit PDM to +/-1 format
+        print(pdm_signal)
+        pdm_signal = pdm_signal.astype(int)
+        #pdm_signal = [2*s - 1 for s in pdm_signal.astype(int)]
+        pcm_signal = cic_decimate(pdm_signal, decimation_factor=decimation_factor, **kwargs) 
+        pcm_signal = numpy.array(pcm_signal, dtype=float)
+
     return pcm_signal
 
 def parse():
@@ -28,6 +83,7 @@ def parse():
     parser = argparse.ArgumentParser(description='Process an input file and write to an output file.')
     parser.add_argument('-i', '--input', type=str, required=True, help='Path to the input file')
     parser.add_argument('-o', '--output', type=str, required=True, help='Path to the output file')
+    parser.add_argument('--filter', type=str, default='fir')
     parser.add_argument('--samplerate', type=int, default=16000)
     parser.add_argument('--oversample', type=int, default=64)
     
@@ -41,10 +97,12 @@ def main():
     out_path = args.output
     pdm_data = load_pdm_file(pdm_path)
 
+    print('loaded', pdm_data.shape)
+
     # Convert to PCM
     oversample = args.oversample
     samplerate = args.samplerate
-    pcm_data = pdm_to_pcm(pdm_data, decimation_factor=oversample)
+    pcm_data = pdm_to_pcm(pdm_data, decimation_factor=oversample, filter_type=args.filter)
 
     # Normalize and save to WAV
     pcm_data = np.expand_dims(pcm_data, axis=1)