Digital audio uses digital signals for sound reproduction. This includes analog-to-digital conversion, digital-to-analog conversion, storage, and transmission.
Digital audio has emerged because of its usefulness in the recording, manipulation, mass-production and distribution of sound. Modern distribution of music across the internet through on-line stores depends on digital recording, and digital compression algorithms. Distribution of audio as data files rather than as physical objects has significantly reduced costs of distribution. However, it has brought about a rise in music sharing through peer to peer networks, which is illegal in many countries as copyright infringement. The Recording Industry Association of America and other organizations claim that music sharing severely harms the profitability of their business.
From the wax cylinder, to the compact cassette, analogue audio music storage and reproduction have been based on the same principles upon which human hearing are based.
In an analogue audio system, sounds begin as physical waveforms in the air, are transformed into an electrical representation of the waveform, via a transducer (for example, a microphone), and are stored or transmitted. To be re-created into sound, the process is reversed, through amplification and then conversion back into physical waveforms via a loudspeaker. Although its nature may change, its fundamental wave-like characteristics remain unchanged during its storage, transformation, duplication, amplification. All analogue audio signals are susceptible to noise and distortion, due to the inherent noise present in electronic circuits.
On the other hand, the digital audio chain begins when an analogue audio signal is converted into electrical signals – ‘on/off’ pulses – rather than electro-mechanical signals. This signal is then re-encoded (rather like a spy might use a code book), in order to combat any errors that might occur in the storage or transmission of the signal. It is this “channel coding” that is essential to the ability of the digital system to recreate the analogue signal upon replay. An example of a channel code is Eight to Fourteen Bit Modulation as used in the audio Compact Disc.
