can then pick up the changes in the magnetic field from the wire and convert them into an electrical current, that is reproduced as audio when connected to a telephone receiver.

Poulsen obtained a Telegraphone patent in 1898, and with his assistant, Peder Oluf Pedersen, later developed other magnetic recorders that recorded on steel wire, tape, or disks. None of these devices had electronic amplification, but the recorded signal was strong enough to be heard through a headset or transmitted