Splitting AudioSegments

Question

Here I am practicing analyzing audio(wav format) in order to remove low volumes in given range and export to new audio. It was formatted to int16 array and max value gave +(some number), min gave -(some number). Now as a result the output audio is too small and i think the problem is in wrong range. So how to choose the right range? I gave it between min/2 and max/2.

from pydub import AudioSegment
import io
import scipy.io.wavfile
import IPython
import numpy as np

w = AudioSegment.from_file("input.wav", format="wav")
a = w.get_array_of_samples()

fp_arr = np.array(a).T.astype(np.int16)
avg = (max(fp_arr)/2).astype(np.int16)
avg2= (min(fp_arr)/2).astype(np.int16)

b=[]

for d in a:
   if d not in range(avg2,avg) :#d<avg2 and d>avg:
      b.append(d)

myarray = np.asarray(b)
wav_io = io.BytesIO()
scipy.io.wavfile.write(wav_io, 16000, myarray)
wav_io.seek(0)

sound = AudioSegment.from_wav(wav_io)
file_handle = sound.export("output.wav", format="wav")

Answer 1

If you reject some samples without replacing them by something, it's normal for the resulting wave to be shorter. If what you plane to do is a kind of noise gate , you should probably replace the eliminated samples by silence instead.

However, a real noise gate, as any dynamic processor , works a little bit differently. First if follows the enveloppe of the signal meaning that it doesn't take into account each oscillation around the axis (if you do that, you'll cut some samples inside each oscillation, meaning several dozen of times per second, which is probably not what you want to do). Instead, a noise gate analyses the variation of amplitude at a highest temporal level. After that step, the resulting enveloppe contains no negative value anymore. When this enveloppe goes below the defined threshold (let's say 0.125 for power, or an equivalent integer value in 16 or 24 bits), it takes a few milliseconds to make a little fade out (it means that it multiply the amplitude by a factor going progressively from 1 to 0). At the contrary, when the signal passes above the threshold again, it reopens the gate with a little fade in.

If you bypass these little fades in/out, the resulting wave will contains unpleasant numeric clicks. If you bypass the enveloppe follower used to smooth the amplitude, you will close the gate a lot too often.