Dangerous sound? What Americans heard in attacks

WASHINGTON » It sounds sort of like a mass of crickets. A high-pitched whine, but from what? It seems to undulate, even writhe. Listen closely: There are multiple, distinct tones that sound to some like they’re colliding in a nails- on-the-chalkboard effect.

The Associated Press has obtained a recording of what some U.S. Embassy workers heard in Havana in a series of unnerving incidents later deemed to be deliberate attacks. The recording, released Thursday by the AP, is the first disseminated publicly of the many taken in Cuba of mysterious sounds that led investigators initially to suspect a sonic weapon.

The recordings themselves are not believed to be dangerous to listeners. Sound experts and physicians say they know of no sound that can cause physical damage when played for short durations at normal levels through standard equipment like a cellphone or computer.

The device producing the original sound remains unknown. Americans affected in Havana reported the sounds hit them at extreme volumes.

Whether there’s a direct relationship between the sound and the physical damage suffered is also unclear. The U.S. says that in general the attacks caused hearing, cognitive, visual, balance, sleep and other problems.

The recordings from Havana have been sent for analysis to the U. S. Navy, which has advanced capabilities for analyzing acoustic signals, and to the intelligence services, the AP has learned. But the recordings have not significantly advanced U. S. knowledge about what is harming diplomats.

The Navy did not respond to requests for comment. State Department spokeswoman Heather Nauert wouldn’t comment on the tape’s authenticity.

Cuba has denied involvement or knowledge of the attacks. The U. S. hasn’t blamed anyone and says it still doesn’t know what or who is responsible. But the government has faulted President Raul Castro’s government for failing to protect American personnel, and Nauert said Thursday that Cuba “may have more information than we are aware of right now.”

“We believe that the Cuban government could stop the attacks on our diplomats,” said White House chief of staff John Kelly.

Not all Americans injured in Cuba heard sounds. Of those who did, it’s not clear they heard precisely the same thing.

The AP has reviewed several recordings from Havana taken under different circumstances, and all have variations of the same highpitched sound. Individuals who have heard the noise in Havana confirmthe recordings are generally consistent with what they heard.

The recording being released by the AP has been digitally enhanced to increase volume and reduce background noise, but has not been otherwise altered.

The sound seemed to manifest in pulses of varying lengths (seven seconds, 12 seconds, two seconds) with some sustained periods of several minutes. There would be silence for a second, or 13 seconds, or four seconds, before the sound abruptly restarted.

A closer examination of one recording reveals it’s not just a single sound. Roughly 20 or more different frequencies, or pitches, are embedded in it, the AP discovered using a spectrum analyzer, which measures a signal’s frequency and amplitude.

To the ear, the multiple frequencies can sound a bit like dissonant keys on a piano being struck all at once. Plotted on a graph, the Havana sound forms a series of “peaks” that jump up from a baseline, like spikes or fingers on a hand.

“What it is telling us is the sound is located between about 7,000 kHz and 8,000 kHz. There are about 20 peaks, and they seem to be equally spaced. All these peaks correspond to a different frequency,” said Kausik Sarkar, an acoustics expert and engineering professor at The George Washington University who reviewed the recording.

Those frequencies might be only part of the picture. Conventional recording devices and tools to measure sound may not pick up very high or low frequencies, such as those above or below what the human ear can hear. Investigators have explored whether infrasound or ultrasound might be at play in the Havana attacks.

The recordings have been played for workers at the U.S. Embassy to teach them what to listen for, said several individuals with knowledge of the situation in Havana. Some embassy employees also have been given recording devices to turn on if they hear the sounds. The individuals weren’t authorized to discuss the situa- tion publicly and demanded anonymity.

Cuban officials wouldn’t say whether the U. S. has shared the recordings with Cuba’s government.

The State Department has said 22 Americans are “medically confirmed” to be affected and that the number could grow. The symptoms and circum- stances reported varied widely, making some hard to tie conclusively to the attacks. The incidents, which started last year, are considered “ongoing.” An attack was reported in late August.

Cuba has defended its “exhaustive and priority” response, emphasizing its eagerness to assist the U.S. investigation.