In total this involves a good hour of recordings, all from 1982, which FOI have been asked to analyse in greater detail.
"The recordings now have renewed relevance and the Swedish Armed Forces therefore wish to clarify exactly what is contained on these tapes", says Hans Granlund, Chief of Staff of the Naval Tactical Staff at Swedish Armed Forces Headquarters.
Much of this material has not been analysed by FOI since the 1980s. Over the intervening years the technology and methods for the analysis of audio tapes have been considerably refined.
"FOI will be analysing a signal which is new to us. We shall be doing this with the aid of the latest technology. We shall also be having another look at the material already analysed", says Matts Gustavsson, Head of the Department of Underwater Research at FOI.
Suggests the presence of a submarine
The controversial recording of sound, suspected to emanate from a submarine, made in Hårsfjärden bay in October 1982 is one of the recordings to be analysed afresh. There are good grounds for supposing that it is a foreign submarine that can be heard on the tape. The recording was made public in December last year.
FOI is to submit a final report on 12 May. The Swedish Armed Forces will then analyse the findings and assess the result.