At Apple’s Worldwide Developers Conference on Monday, the tech giant unveiled an array of new features for its flagship products, from screen-time management tools to security enhancements . But even with this churn, some of the company’s offerings remain constant. Perhaps most notably, its iPhone ringtones are so pervasive and unchanging that a few have seeped into our culture, even as they draw on long-standing musical traditions. That’s very much by design: The composition of their rhythms and notes plays a large part in how they interrupt our lives.

Two of the most instantly recognizable iOS ringtones are “Marimba” and “Xylophone,” sounds that have become comfortable and familiar. But as music theory demonstrates, subtle details in the composition of these tunes all but demand that we cut them off by picking up the phone. That’s partly because they are fundamentally disruptive, intrusively insisting on our attention. Ultimately, the effect may be key to Apple’s cultural impact. With the possible exception of Nokia and its now-historical ringtone, no other company has managed to make the sounds of its devices quite so central to its brand identity.

Consider the ringtone “Xylophone,” which consists of two lines — a cutesy melody on top supported by a constant pulsing layer underneath that sustains your attention. “Xylophone” is composed around the concept of syncopation — accentuating weaker beats to mess with a rhythm a bit and make it more complex. Think: “Buh-buh-bummm, buh-buh-b-b-b-buh” in the upper line, and “bum-bum-bum-bum-bum-bum-bum-bum” consistently in the lower line. These two lines may not seem to match up at first, but the melody fits awkwardly with the supporting tones underneath. The lower line features annoying pulsing beats, while the melody articulates beats that the second line doesn’t hit. In theoretical terms, we would say one line has isochronous rhythms — that is, they are evenly spaced and patterned. By contrast, the line with the syncopated melody uses non-isochronous rhythms. Together, these two patterns create a barrage that aims to unsettle the listener. This is a tune that Apple has stuck with precisely because we don’t want to listen to it.

The “Marimba” ringtone — which was the iPhone’s default for many years — also has two lines, but they fit together more harmoniously. Each one contributes in a more collaborative, less antagonistic way to the music. The base is made up of lower pitches, while higher, accented chords form the upper line: “Buh-buh-BUH-buh-buh-BUH-buh-buh-BUH-buh-buh-BUH.” Together they produce a rhythmic effect that’s similar to the pulsating line of the “Xylophone” tone.

Where “Xylophone” relies on syncopation, though, “Marimba” works through a related compositional element known as hemiola. A hemiola is a specific type of syncopation, featuring three beats where you would intuitively expect two. It’s a fairly common musical technique, one that’s been around for centuries, featuring prominently in the work of 19th-century composers like Brahms, Schumann and Tchaikovsky. It also regularly crops up in popular music — from the opening riff of Led Zeppelin’s “Kashmir” to the chorus of Britney Spears’s “Till the World Ends.” In “Marimba,” the accented upper line creates the hemiola with a group of three notes in syncopation against the groups of two. Further, the counterpoint of the two lines jumps dramatically in pitch range, with the upper line using higher pitches that stick out conspicuously because of the accents against the lower notes in the second line.

Effective ringtones often create “earworms,” short musical excerpts that easily stick in your head. Like “Marimba” and “Xylophone,” Queen’s “We Will Rock You” — one of the great earworms — has two repeating strands of musical activity: the stomping and clapping line, followed by Freddie Mercury’s declamatory lyrics in a freer rhythmic pattern. It’s this combination of brevity, repeatability and layered complexity that makes both pop songs and ringtones so sticky. “The catchiness arises from the chunked and sequential nature of tunes; once they interest an ear, they play themselves through to a point of rest,” music theorist and cognitive scientist Elizabeth Margulis writes of earworms in “On Repeat: How Music Plays the Mind.”

Our iPhones’ ringtones feature a particularly pronounced version of that construction, lasting no more than eight beats (two measures of four), before repeating: These are earworms that are forever eating their own tails. In the process, they interest the ear, but unlike with a poppy earworm that gets stuck in your head, interacting with the phone — by answering or silencing it — ends the intrusion. That’s why the best ringtones intentionally include disruptive and attention-seeking elements.

The best evidence of how effective these compositions can be may be their ubiquity in movies and TV — from shows like “Smash” and “Scandal” to horror movies like “Hush.” “The ringtone generally serves as a cue for the audience to pay attention so that they might follow the narrative shifts arising from mobile communication and/or . . . come to some greater understanding about the characters who possess certain ringtones,” musicologist Sumanth Gopinath writes in “The Ringtone Dialectic.” The moment a phone rings onscreen, fictional and real sonic worlds converge, calling us to attention, like when your dog starts barking at the sound of a doorbell in a TV show.

That’s likely to be true even for those of us who typically keep our phones on silent. These compositions are so compelling that they’ve become fundamental to our collective experience. So enjoy all the new software and Memojis introduced this past week, but don’t forget that the constants are what make Apple products feel so urgent.

Twitter: @alyssa_barna

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