Digital audio recorders were a real break with the century-old traditions of recording in the music industry. Prior to digital audio recorders, there was only one kind of sound recording. After the appearance of digital recording, the world was divided into “analog” and “digital” sounds.
The story of digital recording actually has its roots in the history of computing and telephones rather than sound recording. From the 1930s, onward, telephone companies experimented with ways to break up telephone signals into small pieces rather than continuous flows of electricity. They were looking for ways to “compress” sound and make it easier to send multiple signals over a single wire. This effort was at first unrelated to the development of computers, but by the late 1940s, computer engineers had developed ways to record digital data on magnetic tape.
In the 1950s and 1960s, the technologies for converting sound into digital bits and recording it on tape gradually improved to the point where it became possible to record high-quality sound digitally. But record companies were not particularly interested. It was not yet possible to build an inexpensive consumer device to play a digital recording, and digital tape recorders did not offer any particular advantages over the multi-track analog recorders then being introduced.
Digital Sound for the General Public
Digital sound first reached the general public in 1982 by means of the compact disc (CD format). However digital audio for musicians was still very expensive and mostly only available in commercial studios and universities. Only in the late 1980’s did lower cost, good quality converters become available for personal computers. This development heralded a new era in computer music.
We have now reached the point where most music is distributed digitally (aside from the resurgence of vinyl!) and for just a small outlay you can set up a home recording studio in your bedroom that would have been the envy of many a commercial operation a couple of decades ago.
The Core Concept of Digital Audio Recording
The core concept in digital audio recording is sampling. This is the process of converting continuous analog signals (eg those coming from a microphone) into discrete time-sampled signals. Once the signal has been converted, what you get is an audio file (or a stream of numbers if live-streaming) that represent these sound-waves in the digital domain. These can be streamed to, or stored on, any digital device (like a computer, iPad, digital handheld recorder). This is analog to digital conversion (ADC). Once on your computer, digital audio files can be processed in almost unlimited ways via DSP (digital signal processing).
You then listen back to the digital signals in a reverse of the process when the files are converted back and played through monitors or headphones. This is digital to analog conversion (DAC). The DAC reconstructs the original signal.
The processes of ADC and DAC involve filters to smooth out the results during recording and playback. The quality of the filters is another important difference between less expensive and super professional digital audio recording kit. Here is a non-technical overview and summary of the whole process.
The lowpass antialiasing filter ensures there are no frequencies too high to be correctly sampled during the ADC process. The smoothing filter interpolates the wave form between the discrete samples during DAC.
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