Sound recording and reproduction is an electrical, mechanical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording technology are analog recording and digital recording. Prior to the development of sound recording, there were mechanical systems for encoding and reproducing instrumental music, such as wind-up music boxes and, later, player pianos.
Acoustic analog recording is achieved by a microphone diaphragm that can detect and sense the changes in atmospheric pressure caused by acoustic sound waves and record them as a mechanical representation of the sound waves on a medium such as a phonograph record (in which a stylus cuts grooves on a record). In magnetic tape recording, the sound waves vibrate the microphone diaphragm and are converted into a varying electric current, which is then converted to a varying magnetic field by an electromagnet, which makes a representation of the sound as magnetized areas on a plastic tape with a magnetic coating on it.
Analog sound reproduction is the reverse process, with a bigger loudspeaker diaphragm causing changes to atmospheric pressure to form acoustic sound waves. Oscillations may also be recorded directly from devices such as an electric guitar pickup or a synthesizer, without the use of acoustics in the recording process, other than the need for musicians to hear how well they are playing during recording sessions via headphones.
Digital recording and reproduction converts the analog sound signal picked up by the microphone to a digital form by the process of digitization. This lets the audio data be stored and transmitted by a wider variety of media. Digital recording stores audio as a series of binary numbers (zeros and ones) representing samples of the amplitude of the audio signal at equal time intervals, at a sample rate high enough to convey all sounds capable of being heard.
Digital recordings are considered higher quality than analog recordings not necessarily because they have higher fidelity (wider frequency response or dynamic range), but because the digital format can prevent much loss of quality found in analog recording due to noise and electromagnetic interference in playback and mechanical deterioration or damage to the storage medium. Whereas successive copies of an analog recording tend to degrade in quality, as more noise is added, a digital audio recording can be reproduced endlessly with no degradation in sound quality. A digital audio signal must be reconverted to analog form during playback before it is amplified and connected to a loudspeaker to produce sound.