Digital sound recording and reproduction

Information on digital recording, from the birth of computers with Charles Babbage to modern recording methods such as the CD.

The technology behind digital recording can be traced to 1841 when Augustin-Louis Cauchy first proposed sampling theory. The next year Charles Babbage invented his analytical engine for performing and storing calculations and the age of the computer began. Almost exactly one hundred years later, in 1943, the U.S. Army turned on the first modern computer. The importance of communications meant that the recording of sound was one of the first applications to which computer research was devoted.

In 1950, Richard W. Hamming published information about error detection and correction codes and two years later the "Reed-Solomon" Codes for encoding and reading CD's were published. Without either the modern CD would not work.

In 1958 the laser was invented and digital technology was on the brink of revolutionising sound recording and reproduction. By the turn of the next decade, Sony had introduced the 13-bit PCM digital recorder and Dutch physicist Klass Compaan, working for Philips, had completed a prototype glass compact disc. 

Toward the end of the 1970’s Sony and Philips entered into collaboration on compact disc technology and the standards of 44.1 kHz sampling rate, 16 bit audio sound, disc size and maximum playing time were agreed upon. Soon, with their products ready, the two companies parted and Compact Disc technology was revealed to the world. By 1990, worldwide sales of the CD had reached 1 billion and had overtaken those of the cassette tape.

In digital recording systems sound is stored as a stream of numbers each representing the air pressure at a particular time. An analogue to digital convertor or ADC converts the electrical representations of sound waves into binary numbers usually 16-digits long (1’s and O’s).

To play back the music, the stream of numbers is converted back into an analogue wave by a digital-to-analogue converter (DAC), then amplified and fed into the speakers.

The most common medium for storing digital sound is the polycarbonate Compact Disc. Data exists as a continuous track of pits, 0.5 microns wide, spiraling from the inside outwards. The disc is covered in reflective aluminum that a laser hits in order to read the data. The laser is either reflected by the flat of the disc, or dispersed by a pit. 

An opto-electronic sensor detects the varying dispersions of light and based on their encoded values the CD player reconstructs the original binary code of the recorded sound.

The benefits of digital recording, despite its greater complexity, are flawless reproduction and greater accuracy. As long as the numbers are not corrupted, the analogous sound wave produced will be identical every time and, if a high sample rate is used, the original wave will more closely replicated. What’s more, in the event of damage a digital recording self corrects. If a CD is scratched a digital system can approximately reconstruct the missing data based on the previous and following words.

Also, since nothing touches the encoded portion, the CD is not worn out by the playing process.

Of most excitement for electronic musicians though, is that any binary number can be converted into a sound, meaning that the limitations of physically producible sound no longer exist. Hence there is a greater dynamic range possible than with analogue.

Access to the relatively inexpensive personal computer and its role in the now user-friendly, professional digital recording studio has ensured the dominance of the digital format.