main application with tuning, playing, and GUI

fmdemod3.py

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+import numpy as np
+import sounddevice as sd
+from scipy.io import wavfile
+from scipy.signal import decimate, butter, filtfilt
+
+# Load the raw IQ samples from the file
+filename = "fm_capture6.bin"
+iq_samples = np.fromfile(filename, dtype=np.int8)
+
+# Define the FM demodulation parameters
+sample_rate = int(2e6)  # Sample rate of the IQ samples
+audio_sample_rate = int(48e3)  # Desired audio sample rate
+fm_deviation = int(75e3)  # FM deviation of the radio signal
+channel_width = int(200e3)  # Channel width of the low-pass filter
+
+# Design the low-pass filter
+nyquist_freq = sample_rate / 2
+cutoff_freq = channel_width / nyquist_freq
+b, a = butter(10, int(75e3), btype='low', fs=int(2e6))
+
+# Apply the low-pass filter
+filtered_audio = filtfilt(b, a, iq_samples)
+
+# Demodulate the FM signal
+demodulated_audio = np.diff(filtered_audio.astype(np.float32)) * np.conj(filtered_audio[:-1]).astype(np.float32)
+demodulated_audio = decimate(demodulated_audio, int(100))
+
+# Normalize the audio to the range [-1, 1]
+normalized_audio = demodulated_audio / np.max(np.abs(demodulated_audio))
+
+# Play the audio
+sd.play(normalized_audio, audio_sample_rate)
+sd.wait()
+
+# output_filename = "demodulated_audio.wav"
+# wavfile.write(output_filename, audio_sample_rate, normalized_audio)