Audio of the mysterious ‘sonic attack’ that injured US Embassy officials in Cuba has been released.
Associated Press obtained a recording of the high-pitched noise, deemed to be a deliberate series of attacks in Havana spanning months.
The AP reports the recordings were what led US investigators to suspect that a “sophisticated sonic weapon” or “sonic wave machine” was being used against the diplomats by an unidentified party.
The audio, released on October 13, has been described as sounding like a swarm of electronic crickets.
The recording released by the AP has been digitally enhanced to increase volume and reduce background noise, but has not been otherwise altered.
Listening to the audio records is not believed to be dangerous.
AP reports the US Navy and intelligence services are analysing recordings, but “the recordings have not significantly advanced U.S. knowledge about what is harming diplomats.”
So far, 22 embassy workers have suffered a range of injuries.
Physical symptoms ranged from “ear complaints, hearing loss, dizziness, headache, fatigue, cognitive issues, and difficulty sleeping”, said Secretary of State Rex Tillerson.
US diplomats reported hearing loud noises or feeling vibrations, while others heard and felt nothing but reported symptoms later.
Some diplomats reported being able to escape the noise just by going into a different room or moving to a different spot.
Accoustic experts are reportedly sceptical that a sonic weapon could cause the problem, and Cuba has maintained its innocence over the attacks.
Still, relations with the US became strained when non-emergency personnel at the Havana embassy were evacuated on September 29.
“Until the government of Cuba can ensure the safety of our diplomats in Cuba, our embassy will be reduced to emergency personnel in order to minimise the number of diplomats at risk of exposure to harm,” Mr Tillerson said at the time.
A travel warning was also issued to advise US citizens against visiting the country.
On October 3, the Department of State ordered the departure of 15 Cuban officials from its embassy in Washington, DC.
“The decision was made due to Cuba’s failure to take appropriate steps to protect our diplomats in accordance with its obligations under the Vienna Convention,” Mr Tillerson said in a statement.
“We continue to maintain diplomatic relations with Cuba, and will continue to cooperate with Cuba as we pursue the investigation into these attacks.”
AP used a spectrum analyser to measure the signal’s frequency and amplitude, and found it was not just one single sound. There were roughly 20 or more different frequencies or pitches embedded in the recording.
“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 and engineering professor at George Washington University, who reviewed the recording with AP.
Conventional recording devices may not pick up very high or low frequencies outside of what the human ear can pick up, the report said.