convert numpy int16 audio array to float32
By convention, floating point audio data is normalized to the range of [-1.0,1.0] which you can do by scaling:
audio = audio.astype(np.float32, order='C') / 32768.0This may fix the problem for you but you need to make sure that soundfile.write writes a wav header that indicates float32. It may do that automatically based on the dtype of the array.