VOICEBOX is a speech processing toolbox consists of MATLAB routines that are maintained by and mostly written by Mike Brookes, Department of Electrical & Electronic Engineering, Imperial College, Exhibition Road, London SW7 2BT, UK. Several of the routines require MATLAB V6.5 or above and require (normally slight) modification to work with earlier versions.
In my PhD work, I need to read .NSP voice files and analyze them. So I modified the readwav routine of VOICEBOX to suit my needs. I call my modified routine readnsp.