I have heard of Stereophonic, Monophonic, and Duophonic recordings. But what is a Orthophonic recording? I picked up an original RCA "New Orthophonic" High Fidelity recording from 1958 of "Elvis Golden Records" for 50 cents today at a thrift shop. It looked pretty trashed. but after a Disc Doctor treatment. It came out really nice. (Just a few crackle and pops) It sounds like mono to me. But it sounds good to these ears. My first 50's Elvis Presley LP.