I need to insert 3-dimensional matrices into a new variable.
I'm trying to do that by:
Creating a 4-dimensional matrix and by promoting the fourth dimension saving the three dimensions respectively.

Sample code:

```
from python_speech_features import mfcc  
import numpy as np

X = np.zeros((0,0,0,0),float) #4-dimensional - (0, 0, 0, 0)  
ii = 0  

    for ii in range 1000:  
      data, fs = sf.read(curfile[ii])  
      sig = mfcc(data, fs, winstep=winstep,winlen=winlen,nfft=1024) #size - (49, 13)  
      sig = sig[:, :, np.newaxis] #add third-dimensional - (49, 13, 1)  
      X[:,:,:,ii] = sig

```

Error:

> 
> IndexError: index 0 is out of bounds for axis 3 with size 0
> 
> 
> 

Someone can help me with that problem?