Johnny Cash's pronunciation history
On the recordings I've heard of Johnny Cash, his pronunciation is very proper and I don' hear a strong southern accent. Did he always sing that way or did he have a strong accent and loose it as he did more performances?
A vaguely remembered incident from childhood motivates this question. I recall seeing a segment of the Ed Sullivan show where a country comedian's act consisted of songs that satirized various country and western singers. The act was an embarrasing failure since the urban studio audience didn't understand the material. I recall that he sang "Ring of Fire" and the punch line was apparently the pronunciation of the lines "Ring of Four! Ring of Four!". Did Johnny Cash every pronounced "fire" that way. I've never heard a recording where he did.