Up to the 1970s, all recording technology depended on creating a physical analogue, whether on tape or disk, of the original sound waves. Despite many incremental improvements to these techniques, by the 1970s, further reductions in noise and distortion were becoming increasingly difficult and expensive. As a result, audio researchers began to experiment with digital techniques that had first been exploited in the computer and telecommunication industries. Digitizing an electrical audio signal consisted of first sampling the wave thousands of times a second, measuring the amplitude of each sample, and then assigning one of a limited number of binary values to each. The resulting tape recording consisted of a coded series of on-off signals, or bits. Unlike analogue recording, in which noise and distortion tended to accumulate at each stage of recording and post-production, in digital recording the original message could be cleanly regenerated as long as the simple binary values were recognizable. In addition, minute alterations to the message could be made electronically, by altering the value of individual bits.
The first digital tape recorder was demonstrated in Japan in 1967, with the first digitally mastered records appearing on the Denon label in 1972. The first commercially available digital audio recorder was the Sony PCM-1. Introduced in 1977, the PCM-1 converted an incoming analogue signal into a digital one, which was then recorded onto a standard video cassette in a VCR. Initially, digitally mastered records were still released on vinyl disks in the analogue format. In 1982, however, Sony and Philips released the first compact discs and players. On a CD, the digital information was embodied as millions of microscopic bits in the reflective aluminum coating of the disk. The CD player employed an optical unit to "read" the pattern of bits and convert the resulting electrical pulses into an analogue signal that could drive a speaker. Because the system was optical, friction and noise from physical contact between stylus and record was eliminated. In 1987, another digital format was introduced, the digital audio tape (DAT). Due to record company opposition to a medium that allowed flawless copies of CDs to be made, few DAT recorders were released to the North American public. They did, however, become quite common for professional recording.
Digital recording devices are continually evolving. In the last decade, the most significant, and largely unforeseen, development has been the widespread exchange of digital music files over the Internet. This has been made possible by a number of technical developments, including software for "ripping" songs from commercially released CDs, compression software that reduces the size of these music files by eliminating redundant or unnecessary data (e.g. MP3), and file-sharing software that supports the swapping of these files over the Internet (such as Napster, Kazaa and LimeWire). The popularity of MP3 file sharing, especially among young, technically savvy music lovers with disposable incomes, soon encouraged manufacturers to introduce portable MP3 players. The first of these, the Elger Labs MPMan F10 and the Diamond Rio PMP300 were introduced in 1998. These employed flash memory chips for data storage and had a capacity limited to less than a dozen songs. In late 1999, Remote Solutions introduced the first MP3 player incorporating a magnetic hard-drive, which boasted a capacity of 1,200 songs. This was followed two years later by Apple Computers' iPod. The huge popularity of file sharing has shaken the foundations of the recording industry, whose profit for over a century has depended on restricting the ability of record buyers to make and transmit high-quality, free copies of their products. It is not yet clear what arrangements will ultimately be devised to balance the rights of music creators to compensation with the rights of consumers to reasonable copying and sharing of their products.