How did wire recorders work? — MW, San Diego, CA
The original recording scheme invented by Poulson used a wire as the recording medium, rather than a tape. It recorded audio information as the magnetization of a steel wire in much the same way that a modern tape recorder records audio information as the magnetization of iron particles on the surface of a plastic tape. Both devices record the air pressure changes associated with sound as magnetization changes in a magnetizable surface—the higher the air pressure, the deeper the magnetization in a particular direction; the lower the air pressure, the deeper the magnetization in the opposite direction.