As a kid behind the Iron Curtain I had a radio & cassette tape player with a single large speaker built-in. The cassette player had a record button that when pressed together with play used the speaker and I could actually record my voice, and play it back, from the tape. After enough re-recording on a single tape the fade of the old recordings broke through the new ones creating a truly amazing sound experience. Too bad I lost the tapes and the device.