gspi loads the 'glockenspiel' signal. This is a recording of a simple tune played on a glockenspiel. It is 262144 samples long, mono, recorded at 44100 Hz using 16 bit quantization.
[sig,fs]=gspi additionally returns the sampling frequency fs.
This signal, and other similar audio tests signals, can be found on the EBU SQAM test signal CD http://tech.ebu.ch/publications/sqamcd.