Tapes comes from the mainframe tapes and were popularised by music too. so often people used normal tapes-drives and for a zx81-games - there were even description how you had to connect the microphone-cable to the head-phone-jack and reverse. While loadibg a zx-81 game you hear the whole time the data coming in! so meta: sound was for people and maschines.analog digital. So there was no difference between an accoustic coppler and data from the tape.