import numpy as np
import matplotlib.pyplot as plt
from scipy.signal import ShortTimeFFT

sample_rate = 800.0
duration = 2.0
sample_count = int(sample_rate * duration)
time = np.arange(sample_count) / sample_rate
samples = np.where(
    time < 1.0,
    np.sin(2 * np.pi * 50 * time),
    np.sin(2 * np.pi * 150 * time),
)