Difference Between Phonograph Records And Magnetic Recording
The first phonograph recorded sound on a rotating wax cylinder. Both recording and playback were completely mechanical. To convert sound waves to mechanical motion, a diaphragm was placed in the narrow end of a large horn. Attached to the diaphragm was a needle. Sound waves reaching the diaphragm caused the needle to vibrate, and the needle traced a wiggly groove, analogous to the sound, on the wax cylinder. The rate of the wiggles in the groove reflected the frequency of the sound wave, and their size reflected the amplitude of the sound waves.
In playback, a needle attached to a diaphragm vibrated as it followed the grooves of the rotating cylinder. The sound waves created by the vibrating diaphragm were amplified by a horn, and the sound was reproduced. Later, circular discs replaced wax cylinders as records.
A modern phonograph record is part of an electromechanical system. That is, making and playing phonograph records is partly mechanical and partly electronic. To record sound, a microphone converts sound waves into an electrical signal that is analogous to the original sound. The electrical signal is amplified and used to cause a cutting needle to vibrate on a master disc producing a wiggly groove. The master disc is a precisely flat aluminum disc coated with a plastic material called lacquer. The cutting head is brought over the lacquer and the cutting stylus is lowered to the lacquer’s surface. As the disc turns beneath the cutting head the cutting stylus moves back and forth. At the same time, a precise lead screw moves the head across the surface of the lacquer. Thus, a spiral groove is cut into the surface of the disc.
Playing a phonograph record is much like cutting it. A stylus (needle) held by the phono cartridge fits in the record’s groove. As the record turns, it moves the stylus back and forth. The phono cartridge converts these motions into an electric signal.
The first sound recordings were recorded monophonically. This means that there was only one channel of sound. It was played through one loudspeaker. Many of these recordings were very good, but they did not give the listener a sense of where the musicians were when the recording was made. All modern sound recordings are made stereophonically. A stereo recording has two channels, one for each speaker. In making the recording, at least two microphones are used. They are spaced apart from one another and each picks up a slightly different sound pattern. In a stereophonic record, each wall of the groove contains one channel. A stereophonic phono cartridge responds to both channels with two separate electric signals. When a stereophonic recording is played back on a stereo system, the listener can perceive the slight differences that the original microphones picked up. Although for the most part, vinyl records have been displaced by digital media, such as CDs, they are still manufactured (albeit in smaller quantities)—and often rank as the disc of choice among professional DJs and music aficionados.
Magnetic Recording
Before computers came to dominate the studio, almost every recording required magnetic tape. The magnetic tape was then used to make the record by the process described above. The basic process of tape recording is the same for audio or video.
All tape recorders are constructed similarly. They differ chiefly in such things as tape packaging (cassette or open reel), tape size, recording speed, mobility of play heads, and the recording of either analog or digital signals.
Tape for magnetic recording is thin plastic coated on one side with very fine particles of iron oxide, chromium dioxide, or metal that can be easily magnetized and demagnetized. The coated side of the tape passes over a small electromagnet called the record head. The particles become magnetized as they move by it. The magnetic pattern left by the record head reflects the strength of its magnetic field. That magnetic field, in turn, is controlled by the signal being recorded. The signal can be electrical output from a microphone, complex information contained in a video signal, or on/off impulses of a digital signal. The magnetic pattern on the tape directly reflects the type of recorded signal, whether it is musical, pictorial (TV), or digital information.
In playback, the tape is rewound and then passed forward again over another electromagnet. As the magnetized particles pass over this play head, they make a small current flow in the wire coils of the electromagnet. These faint signals are amplified and sent to loudspeakers, a TV monitor, or digital decoding circuitry.