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Two years after joining Sony as chief of the Audio Technology Center, Nakajima together with Jun Takayama and Hiroyuki Suzukawa began work on the development of digital audio. The building in which they worked was some distance from the Sony head office in which Ibuka worked, making it difficult for Ibuka to see what Nakajima and his colleagues were working on. The distance between the two buildings was enough to allow Nakajima to push ahead freely with his endeavors, unhindered by constant inspection. Nakajima forged on, always mindful of the motto,  Continuity is strength.
To code an analog signal or to establish a digital modulation system, Nakajima continued to work with the PCM (Pulse Code Modulation) that he had used during his time at NHK. This system was based on a concept introduced in 1939 and was the same one used for computers, long-distance telephone transmission and broadcasts to Earth from Apollo space-crafts.
The amount of tape space taken up by digital audio recording is about one hundred times that of an analog audio recording or the same amount of space on a tape used by a broadcast-use VTR. Therefore, conventional analog audio devices could not be used because the tape could not record enough. When a mechanism is made from scratch, this machinery becomes unavoidably large.
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Sony's first PCM digital audio recorder, the X-12DTC, used a 56-channel fixed head. Shown here is the tape transport mechanism during its development stages. |
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Nevertheless, Takayama and Suzukawa toiled to build Sony's first PCM digital audio recording machine, the X-12DTC, was announced in 1974. It used 2-inch wide tape and a fixed head with 56 channels. Although it reproduced sound, the X-12DTC recorder was roughly the size of a refrigerator. The transport unit alone weighed approximately 250 kilograms. Although overly bulky, the creation of the first machine marked the beginning of Sony's history in digital sound recording. The machine was transported to and from various venues to make test recordings of orchestral music. The recorder was also exhibited at the 1974 Audio Fair in Japan. Some audio specialists remarked on the clarity of the machine's sound. In the end, however, the recorder was not marketed, even though producing digital sound through a PCM system with fixed heads represented a revolution in recording technology.
Encouraged by Nakajima's enthusiasm, Toshitada Doi and his colleagues joined the development team and began work on constructing a smaller and cheaper recorder. One of the group members, Akira Iga, had an inspiration. The frequency band used to reproduce video images was more than 200 to 300 times the frequency band of analog audio. Theoretically, this would be sufficient to record the large amounts of information necessary for digital audio. Iga wondered what would happen if he tried to make a digital audio recording using the Betamax home-use VCR, launched in 1975. Nakajima had him try immediately.
Nakajima and his team designed a PCM circuit that would perform large-scale signal processing in order to allow Betamax to record and play back digital sound rather than video images. This was called a PCM Processor, and it appeared to hold great promise. A VCR and a PCM processor used in combination constituted a digital audio tape recording system. This system was displayed at the 1976 Audio Fair and attracted considerable interest.
In September 1977, the PCM processor was marketed as the PCM-1. Although it had to be used in combination with a VCR, it was the world's first product to be commercialized that enabled digital recording and playback. The PCM-1, which was generally intended for home-use, was priced at 480,000 yen.
Despite its high price, the PCM-1 was praised for its sound clarity. A first time listener of the PCM-1 likened its clear, digital sound to removing a thick layer of clothing from analog sound. At the same time, however, the PCM-1 drew much criticism.
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