Combine sounds into one

# combine all individual graph sounds into one waveform

import soundfile as sf
import numpy as np

idle_time = 0.5
graph_duration = 5.0

data, samplerate = sf.read('graphs_clean.wav')
graph_samples = int(graph_duration*samplerate)

last_time = 0
start_points = []
for i, samp in enumerate(data):
    cur_time = i / samplerate
    if np.abs(samp[0]) > 0.001 or np.abs(samp[1]) > 0.001:
        if cur_time - last_time > idle_time:
            start_points.append(i)
        last_time = cur_time

arr = np.zeros((graph_samples, 2))

for point in start_points:
    arr += data[point:point+graph_samples]
arr /= len(start_points)

sf.write('graph_combined.wav', arr, samplerate)