Separate speech signals that are bandlimitted
As mentioned in comments that the 4Khz and 8 Khz bandlimited files are kept separately but in same folder and problem is to segregate them into separate folders.

One can use scripts written in Matlab or Python for doing this, procedure could be as follows : 


Read each file (this could be easily automated in matlab/python) from folder.
split each file into frames, take FFT of frames.
for the 4 Khz band limited files the magnitude of upper half of FFT coefficients will be very less, but for 8Khz magnitude of upper half of FFT coefficients will be significantly high.
the above logic could be automated by keeping fixed threshold on magnitudes of FFT coefficients.
based on above threshold, files could be moved to separate folders.