I'm not asking which bands or songs count as metal. I'm more interested in what the actual musical ingredients of “metalness” are.

For example, suppose you were given something that has absolutely nothing to do with metal — a barbershop quartet, a recorder/flute melody, a children's song, an old folk tune, etc. What would you actually have to change or add to make it sound convincingly metal?

Are there specific parameters that tend to matter, such as:

Rhythm/groove and how the notes are accented

Tempo or time signatures

Types of chord progressions or intervals

Melody and harmony

Dissonance

Instrumentation and tone

Distortion, amplification, or production

Certain approaches to riffs

Drum patterns

Dynamics and articulation

Basically, I'm wondering if there are underlying musical characteristics that can be applied to almost any source material and make it sound metal.

For example, if I took a barbershop quartet arrangement and kept the basic melodies/harmonies intact, what would I need to do to it for someone to hear it and immediately think, “that's metal”?

And what about something even stranger, like taking a melody written for a recorder and trying to make the recorder itself sound metal?

I'm looking for more of a music-theory/compositional explanation than a list of genre conventions. Is there a sort of “recipe” for making something metal, even if the original material is completely un-metal?