Hi. I'm doing my thesis on vocal and non-vocal classification. In the pre-emphahsis step of MFCC, y2 = filter([1, -a], 1, y); what does it mean? I can't relate the code of pre-emphasis with its equation H(z)=1-a*z-1. Help me Please.

a=0.95; y2 = filter([1, -a], 1, y);