In digital recording, an audio or video signal is digitized, converting into a stream of discrete numbers representing the changes over time in air pressure for audio, or chroma and luminance values for video. This number stream is saved to a storage device. To playback a digital recording, the numbers are retrieved and converted back into their original analog audio or video forms so that they can be heard or seen. The digitized number streams themselves are never actually heard or seen, being hidden by the process.
In a properly matched analog-to-digital converter (ADC) and digital-to-analog converter (DAC) pair, there is one and only one analog output that must, by definition, exactly match the analog input. Because the signal is stored digitally, the recording is not degraded by copying, not degraded by storage (assuming proper error detection and correction), and not degraded by interference.
- The analog signal is transmitted from the input device to an analog-to-digital converter (ADC).
- The ADC converts this signal by repeatedly measuring the momentary level of the analog (audio) wave and then assigning a binary number with a given quantity of bits (word length) to each measuring point.
- The frequency at which the ADC measures the level of the analog wave is called the sample rate or sampling rate.
- A digital audio sample with a given word length represents the audio level at one moment.
- The longer the word length the more precise the representation of the original audio wave level.
- The higher the sampling rate the higher the upper audio frequency of the digitized audio signal.
- The ADC outputs a sequence of digital audio samples that make up a continuous stream of 0s and 1s.
- These binary numbers are stored on recording media such as a hard drive, optical drive, or in solid-state memory.
- The sequence of numbers is transmitted from storage into a digital-to-analog converter (DAC), which converts the numbers back to an analog signal by sticking together the level information stored in each digital sample, thus rebuilding the original analog waveform.
- This signal is amplified and transmitted to the loudspeakers or video screen.