John Williams’ score for “Jaws” (1975), considered one of the best soundtracks of all time, centers on a simple two-note motif. The main “shark” theme, which signals impending danger, consists of a pair of alternating notes, identified as either E and F or F and F sharp.

Describing this theme as “grinding away at you, just as a shark would do, instinctual, relentless, unstoppable,” Williams wanted to keep it straightforward. “I just began playing around with motifs that could be distributed in the orchestra, and settled on what I thought was the most powerful thing, which is to say the simplest,” he told film historian Jon Burlingame in an 2012 interview with Limelight magazine. “Like most ideas, they’re often the most compelling.”

When Williams first described the motif to “Jaws” director Steven Spielberg, the filmmaker thought he was joking. “But after Williams explained it to him, Spielberg was sold,” said director Matt Schrader, whose “Score: A Film Music Documentary” touches on “Jaws” and its impact on film music in general. (The movie opens June 16 in New York City and Los Angeles, and then will expand to additional cities.)  “It speaks to trust that directors have with their composers.”

Williams went on to win an Oscar for best original score and credits “Jaws” for “jump-starting his career.” In 2005, the American Film Institute placed “Jaws” at No. 6 on its 100 Years of Film Scores. Quickly becoming a blockbuster, Spielberg’s aquatic thriller almost singlehandedly launched the summer movie release pattern that dominates the industry today. But the success and impact of “Jaws” arguably comes down to two little notes. (Judge for yourself when the Chicago Symphony Orchestra presents live-to-picture concerts of “Jaws” on June 28-30, with Richard Kaufman on the podium.)

Spielberg agrees and later admitted: “I think the score was clearly responsible for half of the success of that movie.”

TOP: John Williams conducts selections from his score of “Jaws” with the Boston Symphony Orchestra last fall. | Photo: BSO

Video: The opening music for “Jaws” (from YouTube)