[Rwp] lowering the pitch of a vast number of MP3 files with Reaper, how to do?

[Beth]

Hi, all.
So just for some clarification, I don't want to play like I know nothing 
about how to alter files with Reaper. However, I will need to do myself 
a huge favor and alter all the Pal audio files in my movie collection. I 
know some things about arming and recording files since I have done so, 
and I have partially produced some files, but not others. Ugh. Anyhow, 
how do you simply lower the pitch of the entire file in MP3 or OGG 
formats? Do you need any special software for MP3 or what? Please fil me 
in. Thanks.
Beth

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