Simple Frequency Shift Keying implementation for digital modulation

fsk.py

import numpy as np
import wave
import struct
from scipy.signal import butter, lfilter

# Function to convert text to FSK and save as a WAV file
def text_to_fsk_wave(text, filename):
    bit_rate = 1200
    freq_low = 1200
    freq_high = 2400
    sample_rate = 48000

    binary_data = ''.join(format(ord(char), '08b') for char in text)
    t = np.arange(0, len(binary_data) / bit_rate, 1 / sample_rate)
    fsk_signal = np.zeros(0)

    for bit in binary_data:
        freq = freq_low if bit == '0' else freq_high
        fsk_signal = np.append(fsk_signal, np.sin(2 * np.pi * freq * t[:int(sample_rate / bit_rate)]))

    fsk_signal = np.int16((fsk_signal / np.max(np.abs(fsk_signal))) * 32767)

    with wave.open(filename, 'w') as wav_file:
        wav_file.setparams((1, 2, sample_rate, 0, 'NONE', 'not compressed'))
        for sample in fsk_signal:
            wav_file.writeframes(struct.pack('h', sample))

# Function to decode FSK WAV file back into text
def fsk_wave_to_text(filename):
    bit_rate = 1200
    freq_low = 1200
    freq_high = 2400
    sample_rate = 48000
    samples_per_bit = sample_rate // bit_rate

    with wave.open(filename, 'r') as wav_file:
        frames = wav_file.readframes(wav_file.getnframes())
        fsk_signal = np.frombuffer(frames, dtype=np.int16)

    fsk_signal = fsk_signal / np.max(np.abs(fsk_signal))
    fsk_signal = bandpass_filter(fsk_signal, freq_low, freq_high, sample_rate)

    binary_data = ''
    for i in range(0, len(fsk_signal), samples_per_bit):
        sample = fsk_signal[i:i + samples_per_bit]
        freq = np.fft.fftfreq(len(sample), d=1/sample_rate)
        fft_vals = np.fft.fft(sample)
        peak_freq = abs(freq[np.argmax(np.abs(fft_vals))])

        if np.isclose(peak_freq, freq_low, atol=10):
            binary_data += '0'
        elif np.isclose(peak_freq, freq_high, atol=10):
            binary_data += '1'

    text = ''
    for i in range(0, len(binary_data), 8):
        byte = binary_data[i:i + 8]
        if len(byte) == 8:
            text += chr(int(byte, 2))

    return text

# Band-pass filter for signal processing
def bandpass_filter(data, lowcut, highcut, fs, order=5):
    nyq = 0.5 * fs
    low = lowcut / nyq
    high = highcut / nyq
    b, a = butter(order, [low, high], btype='band')
    y = lfilter(b, a, data)
    return y

# Example usage
text_to_fsk_wave("Hello World", "hello_world.wav")
decoded_text = fsk_wave_to_text("hello_world.wav")
print("Decoded Text:", decoded_text)