Oona Räisänen is back with more annotated auditory phenomena. This time, it’s a frequency sweep on a cassette tape. She writes:

The tape on a compact cassette imposes all kinds of noise and distortion on a recorded signal. Much of it is so quiet that it’s practically inaudible, but with some signal processing we can zoom into some fascinating details.

Of particular interest are the sidebands caused by variations in the drive mechanism (flutter).