TOKYO -- Japanese toilets have come to be known overseas for their variety of functions, and one has been attracting particular attention of late -- a speaker that produces white noise to drown out any embarrassingly loud eruptions.

The idea for the device actually has its roots in the country's ancient "culture of shame."

During the Tokyo Olympics this past summer, some visiting sports writers reported on devices set up inside toilet stalls that play babbling water recordings.

One reporter raved about the accessory, describing it as "the coolest thing in Tokyo" and going on to say she was "shocked" to hear the burbling. Another described her surprise at hearing a device that played "birds' singing."

In 2013, a U.S. travel agency surveyed 200 foreign female residents in Japan, asking what surprised them most after arriving in the country. The largest number of respondents, or 27%, cited the singing toilets. The second largest group, representing 23%, answered "the large variety of vending machines," followed by 20.5% that said the "presence of large numbers of convenience stores." Another 17% replied that the bidet function of toilets surprised them the most.

But when did the sound device debut? The first such product was marketed 1979 by Orihara Manufacturing, a Tokyo-based maker of toilet accessories. The world's first device that electronically simulates the sound of flowing water and doubles as an air freshener was named Etiquette Tone by company President Seiichi Orihara. As the name suggests, it was devised to drown out the potentially embarrassing sound of the final act of digestion.

In 1988, Toto followed suit by introducing Otohime, which subsequently became a generic term referring to the devices. In Japanese, oto means "sound," and hime "princess," but when pronounced together the syllables form a homonym for the name of a princess of an undersea kingdom in a famous folk tale.

Before developing the product, an internal survey helped the company understand that its female employees were embarrassed not only by their bodies' lack of discretion but by other sounds they make in a stall while disrobing or using female sanitary products.

"We initially used a mechanical sound but since 2011 we've been using a recorded actual gurgle of a stream," product developer Tsukasa Matsuyama said. The device can also overlay bird chirping.

Lixil, which first launched its version of the dulcet device in 1990, also uses a recording of running water. In 2018, it worked with Roland, an electronic instrument maker in the central Japanese city of Hamamatsu, to develop a special gurgling effect for a noise-masking product called Sound Decorator.

"It has a pleasant sound and enhances the performance of drowning out the bodily sound," Lixil representative Shintaro Kawai said.

But the culture of masking the body's indiscretions goes back more than two centuries, to Japan's Edo period (1603-1868).

An actual device used to drown out loud gaseous burbles remains intact, at Rendaiji, an approximately 1,300-year-old Buddhist temple in the western Japanese city of Kurashiki that served as a regular place for worship for local daimyos.

Called otokeshi no tsubo , or "sound-drowning urn," it stands tall in the back of the temple's guest building. It consists of a bronze vessel measuring about 50 cm in diameter atop a 2-meter-high stone column. When opened, a tap attached to the urn's side releases water that hits a baked clay plate placed on the ground. Voila, ancient white noise.

A guest bathroom is located behind the device. When a daimyo of the Ikeda clan stayed in the guest's quarters, his entourage, it is believed, would turn on the tap while the daimyo was in bathroom.

"In the olden days, a suikinkutsu , which rings with a splashing sound, was set up under the baked clay plate to augment it," said Zoju Saeki, the temple's vice abbot. "So the device drowned out the shameful sound with the beautiful sound of water."

The sound-drowning urn was installed in 1799 when the temple was rebuilt after a fire.

"At the time," Saeki said, "the only places that had such a device were Rendaiji and the section in the Edo Castle where the shogun's wife and concubines lived, before it began to be used more widely across Japan.

"But this temple is the only place where it is kept just as it was in the past."

Etiquette Tone and other sound-drowning devices have resurrected the old sound curtains. But the modern accessories have an additional purpose: to reduce water consumption.

Through a survey, Toto found that female respondents flush an average 2.3 times when using a toilet without a sound princess but an average of 1.5 times otherwise. In an office where 400 women work, the device can save an annual 5,500 kiloliters of water and costs of about 3.86 million yen ($34,000), according to the company.

"The original purpose [for Orihara Manufacturing to develop the Etiquette Tone] was to save water consumption," said Iwao Yano, head of the company's sales team. When the product debuted, Tokyo was being hit by an abnormal drought. The Tokyo Metropolitan Government's waterworks bureau chief at the time took an Etiquette Tone to the assembly floor and demonstrated the agreeable tones so members could appreciate the accessory's benefits, according to Yano.

Amid the COVID-19 pandemic, Lixil and Toto have expanded their toilet models with lids that automatically close before flushing, thereby preventing viruses from being splashed up and taking flight. Many water-controlling devices, not just those used in the bathroom, now have contactless features that allow users to operate without touching.

Japan's toilet products, developed by designers attentive to the subtle needs of users, have helped loud bowel movers avoid embarrassment, reduce their water consumption and potentially stay away from viruses. They have taken their place in an ancient toilet culture that is likely to continue to evolve.