构造一个wav文件并使用scipy将其写入磁盘

Question

I wish to deconstruct a wave file into small chunks, reassemble it in a different order and then write it to disk. I seem to have problems with writing it after reassembling the pieces so for now I just try to debug this section and worry about the rest later. Basically I read the original wav into a 2D numpy array, break it into 100 piece stored within a list of smaller 2D numpy arrays, and then stack these arrays vertically using vstack:

import scipy.io.wavfile as sciwav
import numpy
[sr,stereo_data] = sciwav.read('filename')
nparts = 100
stereo_parts = list()
part_length = len(stereo_data) / nparts 

for i in range(nparts):
    start = i*part_length
    end = (i+1)*part_length
    stereo_parts.append(stereo_data[start:end])

new_data = numpy.array([0,0])
for i in range(nparts):
    new_data = numpy.vstack([new_data, stereo_parts[i]])
sciwav.write('new_filename', sr, new_data)

So far I verified that new_data looks similar to stereo_data with two exceptions: 1. it has [0,0] padded at the beginning. 2. It is 88 samples shorter because len(stereo_data)/nparts does not divide without remainder.

When I try to listen to the resulting new_data eave file all I hear is silence, which I think does not make much sense.

Thanks for the help! omer

Answer 1

It is very likely the dtype that is different. When you generate the zeros to pad at the beggining, you are not specifying a dtype, so they are probably np.int32 . Your original data is probably np.uint8 or np.uint16 , so the whole array gets promoted to np.int32 , which is not the right bit depth for your data. Simply do:

new_data = numpy.array([0,0], dtype=stereo_data)

I would actually rather do:

new_data = numpy.zeros((1, 2), dtype=stereo_data.dtype)

You could, by the way, streamline your code quite a bit, and get rid of a lot of for loops:

sr, stereo_data = sciwav.read('filename')
nparts = 100
part_length = len(stereo_data) // nparts 

stereo_parts = numpy.split(stereo_data[:part_length*nparts], nparts)

new_data = numpy.vstack([numpy.zeros((1, 2), dtype=stereo_data.dtype)] +
                        stereo_parts)

sciwav.write('new_filename', sr, new_data)