History of Catholic Oppression, Headbanger Edition

A friend sends along this article on the tritone, the flatted fifth or augmented fourth in musical intervals. Fun piece, but has the usual historical ignorance about things medieval in the summary:

A new film about the history of heavy metal highlights the so-called Devil's Interval, a musical phenomenon suppressed by the Church in the Middle Ages.

No reference is provided, so it's impossible to tell what is being referred to. Color me skeptical about this. It's unlikely that people were tortured for compositions that used tritones.

I recall studying rules for voicing four part harmonies, and parallel fifths and octaves were "against the rules." It would be disingenuous to write that "music theory teachers suppressed parallel fifths in the twentieth century." In fact, the article itself notes that this interval (which is quite dissonant) was used "in presenting the devil [o]r . . . to portray the crucifixion."

But, for the record, I dig tritones. "Purple Haze" may be the definitive rock tritone intro. King Crimson also made a career out of the tritone. And you have to dig the name "Professor John Deathridge." Makes you want to be in a metal band with him (he has to skip the first name).