Change the volume of a wav file in python

Question

I have a 2 seconds 16bit single channel 8khz wav file and I need to change its volume.

It should be quite straightforward, because changing the volume is the same as changing the amplitude of the signal, and I just need to attenuate it, that is to multiply it for a number between 0 and 1. But it doesn't work: the new sound is lower but VERY full of noise. What am I doing wrong?

Here is my code:

import wave, numpy, struct

# Open
w = wave.open("input.wav","rb")
p = w.getparams()
f = p[3] # number of frames
s = w.readframes(f)
w.close()

# Edit
s = numpy.fromstring(s, numpy.int16) * 5 / 10  # half amplitude
s = struct.pack('h'*len(s), *s)

# Save
w = wave.open("output.wav","wb")
w.setparams(p)
w.writeframes(s)
w.close()

Thank you guys!

Answer 1

As you can see in the comments of the question, there are several solutions, some more efficient.

The problem was immediately detected by Jan Dvorak ("the * 5 part is clipping and overflowing") and the straightforward solution was:

s = numpy.fromstring(s, numpy.int16) / 10 * 5

In this case, this solution was perfect for me, just good enough.

Thank you all folks!