My processor is the reason for slow pitch conversion. Can you help with batch conversion?

I want to change pitch -0.31 on all my music tracks. This take time. A fifteen minute track takes an hour. I want to accelerate the process by batch conversion overnight. I tried batch conversion by choosing "Lower Pitch" in the Batch Process box. I did this for a couple of Frank Sinatra tracks. He sounded worse than William Hung trying out for American Idol! What am I doing wrong?