At the end of September, the Department of State announced that it would recall half of its diplomatic personnel from the U.S. Embassy in Cuba following the sickening of 21 employees by “specific attacks.” A mysterious sonic weapon had left at least 10 American diplomats with injuries from hearing loss to brain trauma and nervous-system damage. Just weeks before, Secretary of State Rex Tillerson had stated he was evaluating whether to shutter the embassy altogether amid the continued incidents.

“The health, safety, and well-being of our embassy community are our greatest concerns,” the State Department said in a Sept. 27 statement. “Investigations into the attacks are ongoing, as investigators have been unable to determine who or what is causing these attacks.”

So what exactly does this deadly aural assault actually sound like? Thanks to a new recording from the Associated Press, we now have an idea:

The recording, vaguely described by the AP as “what some U.S. Embassy workers heard in Havana,” is currently in the hands of Navy acoustic specialists and “intelligence services.” (The Navy did not immediately respond to request for comment from Task & Purpose.) To date, a total of 22 U.S. government personnel have been sickened by the phenomenon.

The recording seems to rule out some previous theories regarding the illnesses’ cause. Multiple previous reports from the Associated Press (and obstinatecomments from the State Department) characterized the incidents as caused by an “an advanced sonic weapon that operated outside the range of audible sound” — something the AP recording clearly is not, despite being “digitally enhanced to increase volume and reduce background noise.” (That’s not as bad an explanation as “mass hysteria,” which was floated by the Guardian newspaper hours before the AP recording dropped.)

If the recordings themselves “are not believed to be dangerous to those who listen” over a computer or smartphone speaker, as the AP reported, it’s hard to believe they’d cause significant physical trauma even if blasted through something like, say, the non-lethal Long Range Acoustic Devices (LRADs) that the U.S. military and local law enforcement have used for hailing and crowd control.

Americas photo

Sailors get hands on training on the Long Range Acoustic Device (LRAD) onboard the amphibious dock landing ship USS Ashland (LSD 48) on July 24th, 2015.Photo via DoD

According to experts consulted by The Guardian, one possible explanation is ultrasound, frequencies higher than 20 kHz that, while beyond the range of human hearing that, were enhanced to the point of innocuous audibility by the AP. It’s certainly possible: In 2014, a University of Auckland acoustic researcher managed to capture a recording of a mysterious “Hum,” a low-frequency vibratory phenomenon that has been driving people around the world nuts for decades.

But there’s a big problem: As Wired observed on Oct. 5, acoustic scientists aren’t totally sure that high-frequency ultrasound or even very-low-frequency infrasound could inflict the traumatic injuries and neurological problems described by the State Department.

Frankly, even the private-sector defense contractors who work with sonic weaponry aren’t buying it. When I caught up with David Schnell, vice president of business development at LRAD and a retired Navy captain, showing off the company’s latest wares at the Association of the U.S. Army in Washington on Oct. 9, he laughed off my questions about the saga unfolding in Cuba.

“Whatever it is, it’s not on the hearable spectrum,” Schnell said. “We really don’t know. It could be environmental. It could be chemical. But it’s very, very hard to believe it’s acoustic.”

“That’s not what these were designed for anyway,” he added, pointing to the LRAD devices on display. “These are for communication. It’s communication that can solve conflicts before they escalate into lethal force. And in crowded battlefields where there are combatants and noncombatants layered on top of each other, lethal force is a last resort.”