The audio recording: a minimal history (part three)

Magnetic period (1945-1975)To get to the third stage in the development of audio recording, it is necessary to reach the end of World War II, thus in 1945, when the Allied nations gained access to a German invention: magnetic tape recording. The technology dated back to the 1930s and had been constantly perfected by AEG engineers in cooperation with the chemical company IG Farben until it reached maturity represented by the recorder model “K1,” however it had remained confined to German territory where it was used in radio broadcasting until the end of World War II. In 1943, AEG had developed a stereophonic version. It is interesting to note that in the Allied nations there was suspicion of the existence of such technology since broadcasts of symphony concerts, obviously pre-recorded, were often intercepted, characterized by such a high audio quality that they were practically indistinguishable from live broadcasts, as well as by a duration far superior to that obtainable from a 78 rpm record. The fact then that these concerts were regularly rebroadcast turned suspicion into certainty. At the end of the war, the Allies were able to get their hands on a number of German Magnetophon recorders, requisitioned from Radio Luxembourg, which incorporated all the key technological features of analog magnetic recording, particularly the use of high-frequency bias.¹

Mullin and CrosbyThe website of the Crosby Fan World organization reports. a series of interesting information regarding the development of tape recording technology and the special relationship developing between a sound engineer and a great postwar artist-Bing Crosby². Audio engineer John T. MullinThe³ at⁴, serving in the U.S. Army, was sent to Paris in the last months of World War II with the assignment of finding out all he could about radio and electronic technologies developed by the Germans. Mullin’s unit quickly found hundreds of low-quality magnetic dictaphones, but it was a chance visit to a recording studio near Frankfurt that allowed him to get his hands on two items of great interest. These were the large AEG Magnetophon high-fidelity recorders and as many as fifty recording reels. Once transported to the United States, Mullin worked over the next two years on these machines, modifying them and improving their performance. His goal was to convert Hollywood studios to the use of magnetic tape for recording movie soundtracks, which until then had been made on disc.Mullin gave a couple of public demonstrations of his machines that caused a stir among industry insiders: listeners could not believe that what they were hearing was not a live performance. Quite coincidentally, at the second demonstration Mullin gave at MGM studios in Hollywood, there was in the audience Murdo Mackenzie, then technical director of singer, actor and comedian Bing Crosby, who arranged for Mullin to meet Crosby in June 1947 for a private demonstration of his tape recorders. Crosby was astounded by the sound quality and immediately saw the enormous commercial potential of those machines. Live music was the standard for American radio at the time, and the major radio networks did not allow the use of disk recording in their programs because of poor sound quality. Crosby, who disliked the rigidity of live broadcasts preferring the relaxed atmosphere of the recording studio, had asked NBC to let him pre-record his 1944-1945 series on discs, but the network had refused. He had then retired from live radio for that season, returning, not without reluctance, in the 1946-1947 season.

Mullin’s tape recorder thus arrived at the perfect time: Crosby realized that the new technology would enable him to pre-record his radio program with sound quality that equaled live broadcasts and that these tapes could be played back several times without appreciable loss of quality. Mullin was asked to record a test show and was immediately hired as Crosby’s chief engineer to pre-record the rest of the series.

Bing Crosby became the first major American music star to use tape to pre-record radio broadcasts and the first to burn commercial recordings to tape. In addition, radio programs thus recorded were meticulously edited by splicing together many clips to give them a rhythm that was unprecedented in radio.

Crosby personally invested $50,000 USD in Ampex, a small company that quickly became a world leader in the industry, revolutionizing radio and recording with its famous Ampex Reel Tape Recorder model 200 (Fig. 7), introduced in 1948 and developed from Mullin’s modified magnetophones. Equally important was the development of magnetic tape media conducted by the Minnesota Mining and Manufacturing Corporation (now known as 3M).

Thanks to magnetic tape, sound recording made a further qualitative advance and, from 1950 onward, became the standard medium for recording masters in the radio and music industries. This technology also led to the development of the first hi-fi stereo recordings for the home market, the development of multitrack recorders, and the discontinuation of the record as the main mastering medium. The magnetic tape also has brought about a radical rethinking of the recording process: it made possible recordings of much longer duration and offered sound engineers a multitude of tools for a “creative” approach to recording: sounds captured on tape could finally be manipulated sonically, edited and combined in ways impossible with recordings on disk.

Finally, let us point out some important inventions that saw the light of day during this period: the Klipschorn loudspeaker system was patented in 1945, introducing a new concept of the acoustic speaker and marking the beginning of the era of home hi-fi. In December 1947, at Bell Telephone Laboratories, semiconductor experiments led to the birth of the bipolar transistor. The first 12-inch 33 rpm microgroove LP (Long Playing), with a capacity of 23 minutes per side, recorded with Philco production equipment, was unveiled in June 1948 by Columbia. The following year was the turn of the 7-inch 45 rpm introduced by RCA-Victor; from this time on, most record labels would record only on three rotation standards: 33, 45 and 78 rpm. In 1949, the U.S. company McIntosh’s first power amplifier was marketed: the 50W1 Unity Coupled Amplifier, which employed a pair of 6L6 tubes in a Push Pull configuration for an output power of 50 watts. In 1951 Stefan Kudelski, a talented engineer who was only 22 years old, developed the prototype of a very high-quality miniaturized audio recorder that he simply called the Nagra I, which, together with the Grundig Reporter, ushered in the era of Live recordings on magnetic tape.

Multitrack recording

The next development enabled by magnetic tape technology was multitrack recording, in which the tape is divided into several parallel tracks that remain necessarily synchronized, being carried on the same medium. The first fallout of this technique was stereophony, achieved by dividing the recording head into two tracks corresponding to the left and right channels. Developed in Germany in 1943, two-track recording was quickly adopted for modern music in the 1950s because it allowed signals from two or more microphones to be recorded simultaneously but separately (while the use of multiple microphones to record on the same track had been common since the Electric Period, thus since 1925), this allowed stereophonic recordings to be made and edited. Stereo (two-microphone or multimix) quickly became the standard for classical commercial recordings and radio broadcasts, while pop music and jazz continued to be released in mono until the mid-1960s.

Much of the credit for the development of multitrack recording should be given to guitarist, composer and technician Les Paul (Fig. 8), a pseudonym for Lester William Polfuss (1915 – 2009), who moreover helped design the famous electric guitar marketed by Gibson that bears his name. His experiments with tapes and tape recorders in the early 1950s led him to formulate a request for the creation of the first custom eight-track recorder made by Ampex. The pioneering recordings made with his wife, singer Mary Ford, were the first to use the multitrack technique to record elements of a piece of music separately in asynchronous mode, that is, taken at different times. This technique allowed Les Paul to listen to tracks he had already recorded while recording new parts in time along with them.

Multitrack recording was exploited commercially by Ampex, which made a three-track recorder that proved extremely useful in pop music because it allowed the backing track to be recorded on two tracks (by overdubbing separate parts or a full stereo base), while the third track was reserved for the lead singer. Three-track recorders experienced considerable popularity until the mid-1960s, and some famous pop recordings-including many of Phil Spector‘s Wall of Sound productions as well as early Motown Records hits-were recorded on three-track Ampexes. The next development was four-track recording, which offered sound engineers and musicians far greater flexibility for recording and overdubbing. The four-track was the studio standard for most of the late 1960s, and many of the Beatles’ and Rolling Stones’ most famous recordings were recorded with those machines. In particular, the engineers of the celebrated Abbey Road Studios London (Fig. 9) developed a technique called the reduction mixes (bouncing down in the U.S.), in which several tracks recorded on one four-track machine were mixed together and transferred to a single track on a second, also four-track machine. In this way it was possible to record dozens of separate tracks and combine them into recordings of great complexity. All Beatles recordings from the mid-1960s, including the albums Revolver and Sgt. Pepper’s Lonely Hearts Club Band, were recorded with this technique. The accumulation of noise during the process was the limitation of that technique, and the engineers at Abbey Road became famous for their ability to create dense multitrack recordings while keeping that noise to a minimum.

The four-track tape also enabled the development of quadraphonic sound, in which each of the four tracks was used to simulate 360-degree surround sound. Numerous albums were released in both stereo and quadraphonic formats in the 1970s, yet this recording technique did not gain wide public acceptance because of the need to install a second pair of speakers, with associated amplification, in order to be properly enjoyed. Nevertheless, it can be considered the direct progenitor of the surround sound that is the standard in today’s home theater systems.