Mr. Burwell found that most musical instruments didn’t fit with the minimalist sound sculpture he had in mind, so he used singing bowls, standing metal bells traditionally employed in Buddhist meditation practice that produce a sustained tone when rubbed. For one of the few interior scenes with score — Chigurh menacing a service-station owner with a fateful coin flip — he tuned the music’s swelling hum to the 60-hertz frequency of a refrigerator.
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