A church bell rang in the raining distance before thunder cracked and heavy metal took its first breath. Five decades on, the self-titled opener from Black Sabbath’s genre-spawning debut is as chilling now as it was upon release. Its core three notes utilised the devil’s tritone, a clash that could strike fear in the heart of the listener, a sound so dissonant it was discouraged, some even say outlawed, by the religious authorities. It would be the song that convinced Tony Iommi to commit himself to a new sonic evil, paving the path for all heavy noise to come…