Blyth's warbler, (Acrocephalus dumetorum)
This bird is common in the Baltic area and a few males visit Sweden during June. It is active singing all day, but mostly when dark. A learning experiment can be done with this recording: Even if the bird is singing a solo, without other singing birds around - there is a quite audible difference between stereo and mono. Try it! The recording is stereo - copy one channel and make a mono file. Compare.