Analog vs. Digital Recording

Sound is created by vibration. This vibration may be caused by vocal chords, which vibrate when air is passed over them inside the throat, by musical instruments that are plucked or bowed (violins, violas, cellos, double-basses), struck (percussion instruments) or blown through (woodwind and brass instruments). In each case vibration is set into motion. A string vibrates. A drum head vibrates. A reed vibrates in an oboe or clarinet. Or a column of air vibrates inside a flute, trumpet or trombone. Wind can cause vibration, too, as can the operation of an electric engine, walking across a floor or using a tool that creates friction in contact with another object. In other words, many parts of both the natural and manmade environment can create vibrations that can be heard by the ear.
Many of these vibrations will not be heard without the use of amplification, however. A violin string being bowed would actually be difficult to hear if it were not for the resonating chamber (the body of the violin) that the string vibrates through the bridge. The human voice depends on the resonation of sinus passages and the throat and mouth for its resonance. Resonance is actually amplified sound. And electronic musical instruments depend, of course, on amplifiers attached to speakers to provide listenable sound. And hearing aids also amplify sounds to a level detectable by the eardrum, middle ear and auditory nerves that have atrophied, aged, or been damaged.
This sound traveling through the air and detectable by the ear can be live or recorded. If sound is to be recorded (on a vinyl record, reel-to-reel or cassette tape, digital audio tape (DAT), CD, DVD, MiniDisc, floppy or hard disc, or videotape, then there must be some means to translate the sound waves into a form that can represent them in another way. That is what recording is all about. Each of the systems developed for recording these waves has had a certain measure of fidelity. It is has not been a constant progression of ever-increasing fidelity, either, as some systems (for instance, the MiniDisc, use compression while recording, while others (for instance, the DVD) depend on compression to allow the amount of data recorded to be increased). Some people continue to prefer the sound of older systems of recording over the latest ones. Over the years engineers have developed various media to record sound. The earliest ones used needles scratching a wavy pattern into a cylinder of tin, and then wax, and later on platters made of various substances, including metal and vinyl. During the Second World War wire recording was used in the field. Wire recorders were similar to what later became tape recorders, but used thin wire as the recording medium.
The Ampex Corporation developed tape recording in 1948 and the reel-to-reel, and later cassette and 8-track, tape decks were introduced. For field recording the reel-to-reel Nagra became the broadcast journalism standard.  
There are two fundamentally different systems available for recording sound. The first is the system that has been used since the beginning of recording--what is referred to as analog recording. All the devices mentioned above are analog recorders of one sort or another. Analog recording is so called because it is a system that attempts to reproduce the sound waves occurring in the air by creating an "analogy" or similar wave in another form. Analog recording depends on particles of iron ferrite that are suspended in a solution to move or orient themselves in response to a magnetic field. When a person speaks into a microphone, for instance, the mike transduces the sound wave into an electric current whose strength varies according to the amplitude (or power) of the original source. This current passes into, say, a tape recorder and alters the magnetic characteristics of a recording head responding to these differing voltages. As the tape passes over the head the iron ferrite particles move about in response to the changing magnetic field. When played back, the play head creates electrical current in response to these oriented particles. This current passes to the amplifier which, in turn, drives the speakers and recreates the sound wave that then can be heard by the ear.