The English Wikipedia page, to me, seems to suggest that the record was played to explode the mines in a controlled fashion. In fact, according to Finnish Wikip

The English Wikipedia page, to me, seems to suggest that the record was played to explode the mines in a controlled fashion. In fact, according to Finnish Wikipedia, it was used to scramble the Soviet radio signals to prevent the mines from exploding, and there was a sort of radio war going on for a while. This is the specific record that apparently was used: https://www.youtube.com/watch?v=gZx1zl_sVTI https://www.youtube.com/watch?v=gZx1zl_sVTI