Three inventions in one
The tape recorder is not a single invention but a chain of them. Someone had to show that sound could be stored magnetically, someone had to find a practical material to hold it, and someone had to make the sound good enough that people wanted to use it. Each step took a different person or team and several decades.
Smith’s proposal
The idea was first described in print in 1888 by the American engineer Oberlin Smith, who suggested recording sound signals by magnetizing a thread of cotton or silk with steel dust. He did not build a working machine, as far as is documented. The proposal is interesting because it set out the basic principle years before it was demonstrated.
Poulsen and the telegraphone
Valdemar Poulsen, an engineer working for the Copenhagen Telephone Company, built the telegraphone in the late 1890s and received a patent in 1898. It recorded on a steel wire that was drawn past an electromagnet. Its intended purpose was telephony, and he presented it as a way of recording telephone messages when the person called was absent, an early form of message recording that anticipated later telephone answering machines. At the Paris exposition of 1900 the device attracted notice, and recordings reportedly included the voice of Emperor Franz Joseph of Austria.
The telegraphone had serious limits. The recorded signal was very weak, there was no practical way to amplify it until vacuum tubes became common, and the sound was noisy and distorted. The reasons for the distortion were not well understood until later. As a result, the device was a curiosity for some years.
The bias discovery
A decisive improvement was the use of a high-frequency signal, called bias, added to the audio signal during recording. This overcomes a nonlinear magnetic response of the recording material and makes the recorded sound much cleaner. Patents describing AC bias were filed by different people in the 1920s, and it appears that the technique was independently found more than once. In Germany, Walter Weber and his colleagues at German radio refined and used it from around 1940, and the improvement is generally regarded as the main reason that the German tape recorders of the war years sounded as good as they did. Details about who deserves credit are debated.
In the United States, Marvin Camras, working in Chicago, developed advanced wire recorders and made important contributions to magnetic recording, including work on bias, and wire recorders were used by the military in the 1940s. Wire was cheap, but it tended to tangle and was hard to edit.
The Magnetophon
In 1928 Fritz Pfleumer, an Austrian-German engineer, patented a tape made by coating paper with fine metal powder. The German electrical company AEG then developed a recorder to use it, while BASF produced a plastic-based tape. The result, the Magnetophon, was shown publicly in 1935. Engineer Eduard Schuller is credited with a ring-shaped recording head that helped improve the design.
During the war, German radio broadcasting used improved machines with bias for high-fidelity recordings. Allied technicians who examined captured equipment in 1945 were struck by how natural the recordings sounded. These accounts, while widely repeated, come largely from recollections after the war, and how much the quality surprised listeners has probably been somewhat dramatized.
Postwar adoption
The American engineer Jack Mullin, who served in the Signal Corps, encountered German machines in 1945 and brought two of them, along with a quantity of tape, home to California. After demonstrations to engineers and film people in 1946 and 1947, he attracted the attention of Bing Crosby, who had been looking for a way to pre-record his radio program with better quality than disc recordings could offer. Crosby’s company backed the development of recorders at Ampex, a small California firm, which began selling professional machines in 1948. Mullin worked with Crosby on recordings for radio.
Broadcasters and recording studios adopted tape quickly. It allowed editing, long takes and rerecording, while disc cutting could not. By the early 1950s, many American studios and broadcasters were using tape. Meanwhile, manufacturers such as 3M began selling their own tape.
Why the studios cared
Several practical changes to studio production explain the speed of adoption:
- A performance could be recorded in a single take of much longer duration than a disc side allowed.
- Mistakes could be edited out by cutting and splicing the tape.
- A recording could be copied and played back with little loss of quality compared with the existing alternatives.
- Radio programs could be recorded and aired later in different time zones.
What remains uncertain
The exact order of the independent discoveries of bias, the precise roles of the Weber group and others, and some of the details of Mullin’s story come from partial or later accounts. It is accurate to say that Poulsen demonstrated magnetic recording in the 1890s, that German engineers developed high-quality tape recording before and during the war, and that the technology was taken up in American studios and broadcasting after it.