Forensics clean all except voices

[cutdeep46]

I have some tapes that i need to clean all but the voices I was told that voices are from 400 to 25-2600 mhz is there a formula for cleaning audio tapes these tapes were dubbed with a 4 track recorder (voices ) were put on How can I clean all the garbage out (what filters & what order) then what is the best sample rate to save said files? thank you Dale