Low-fidelity magnetic wire recorders had been in use since around 1900 and in the early 1930s the movie industry began to convert to the new optical sound-on-film recording systems based on the photoelectric cell. It was around this time that the German electronics company AEG developed the first practical audio tape recorder, the "Magnetophon" K-1, which was unveiled at the Berlin Radio Show in August 1935.
During World War II, Walter Weber rediscovered and applied the AC biasing technique, which dramatically improved the fidelity of magnetic recording by adding an inaudible high-frequency tone. It extended the 1941 'K4' Magnetophone frequency curve to 10 kHz and improved thedynamic range up to 60 dB, surpassing all known recording systems at that time.
As early as 1942 AEG was making test recordings in stereo. However these devices and techniques remained a secret outside Germany until the end of WWII, when captured Magnetophon recorders and reels of Farben ferric-oxide recording tape were brought back to the United States by Jack Mullin and others. These captured recorders and tapes were the basis for the development of America's first commercially made professional tape recorder, the Model 200, manufactured by the American Ampex company with support from entertainerBing Crosby, who became one of the first performers to record radio broadcasts and studio master recordings on tape.
Magnetic audio tape opened up a vast new range of sonic possibilities to musicians, composers, producers and engineers. Audio tape was relatively cheap and very reliable, and its fidelity of reproduction was better than any audio medium to date. Most importantly, unlike discs, it offered the same plasticity of use as film. Tape can be slowed down, sped up or even run backwards during recording or playback, with often startling effect. It can be physically edited in much the same way as film, allowing for unwanted sections of a recording to be seamlessly removed or replaced; likewise, segments of tape from other sources can be edited in. Tape can also be joined to form endless loops that continually play repeated patterns of pre-recorded material. Audio amplification and mixing equipment further expanded tape's capabilities as a production medium, allowing multiple pre-taped recordings (and/or live sounds, speech or music) to be mixed together and simultaneously recorded onto another tape with relatively little loss of fidelity. Another unforeseen windfall was that tape recorders can be relatively easily modified to become echo machines that produce complex, controllable, high-quality echo and reverberation effects (most of which would be practically impossible to achieve by mechanical means).
The spread of tape recorders eventually led to the development of electroacoustic tape music. The first known example was composed in 1944 by Halim El-Dabh, a student at Cairo, Egypt. He recorded the sounds of an ancient zaarceremony using a cumbersome wire recorder and at the Middle East Radio studios processed the material using reverberation, echo, voltage controls, and re-recording. The resulting work was entitled The Expression of Zaar and it was presented in 1944 at an art gallery event in Cairo. While his initial experiments in tape based composition were not widely known outside of Egypt at the time, El-Dabh is also notable for his later work in electronic music at the Columbia-Princeton Electronic Music Center in the late 1950s.