Changing pitch without changing tempo in an evp

For whatever reason I'm not hearing anything on these EVPs. It could be me, it's late lol. I like the idea of switching the pitch though. I think when it comes to paranormal research, it's not a hard science, and thinking outside the box is really important.

Has anyone ever tried changing the pitch without changing the tempo on an evp? I
recorded a series of evps that I could easily amplify, change speed, or remove noise on to figure out what they were saying. But one particular one, no matter how amplified, slowed down, sped up, or filtered, I still couldn't figure out what it said, it was too muffled, but to me it sounded like a female voice. So I tried something different and I changed the pitch on the evp by around 140 percent and clear as day could hear a female's voice with an intelligent answer. We said to talk into the red light and the voice says, "How are you?"the difference in clarity in simply remarkable and I was wondering if this process is recommended or not in evp evaluation. Thanks alot!