There were operators in charge of transcribing audio from dictation machines
The dictation machine is a special kind of sound recorder that was invented around the 1890s. These are special for making voice recordings because the resulting tape can be edited. In the early 20th century, dictation machines were all the rage among both professionals and ordinary people so they could record voice letters.
The problem came when these people needed to send those voice letters. That is why these records were sent to a secretary, who transferred them to paper with a typewriter. There are many uses for dictation machines even today. However, these days, our phones or computers can automatically transcribe audio recordings.