I had a friend back in the early 90's who was going to give some kind of a talk in a church about the dangers in modern popular music. In this talk he had planned on spending some time discussing messages (backward or subliminal or something like that) embedded in the music.
Note: I am aware that "backward messages" are technically likely different from "subliminal messages"; I just do not remember which one of these that friend was going to discuss in his talk.
He showed me a cassette tape that he said he had gotten from some recording studio. When he played this tape I could hear a murky, somewhat unclear, voice saying something like "decide to smoke marijuana".
This friend explained to me that, in order to prepare for this talk, he had taken the song "Another one bites the dust" (by Queen) to a recording studio and that they had extracted the message out of it.
It's basically the same claim as in this old newspaper article (for reference see column 3, paragraph 3).
Note: I am aware that the label has denied that any messages like this are embedded in this song. My purpose with this question is not to prove or disprove the existence of such messages.
Years later another friend of mine told me that this guy would have had to have access to the original master for this song. Most likely he would not have had access to the studio master tape.
So I am suspecting that the recording studio had played a prank with him (or perhaps he even had asked them to produce a tape like that, in an attempt to prove something).
On another hand, extracting backwards messages from an LP may be quite simple once the location of the messages is known (as it seems to only require slowly rotating the LP backwards).
The question I wanted to ask is: to what degree would ability to extract embedded messages from a song depend on having the original studio master for the song?