The Sound recording reference article from the English Wikipedia on 24-Apr-2004
(provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Sound recording

Learn about Africa online
Methods and media for sound recording are varied and have undergone significant changes between the first time sound was actually recorded for later playback until now.

Table of contents
1 Technology
2 Technique

Technology

Mechanical Recording

The first devices for recording sound were mechanical in nature.

In 1796 a Swiss watchmaker named Antoine Favre described his idea for what we now call the cylinder musical box. This can be considered an early method of recording a melody, although it does not record an arbitrary sound and does not record automatically. "Playback" however is automatic.

The Player piano was a device that could playback a piano performance which had earlier been mechanically recorded onto a piano roll.

The first recording of sound waves

Leon Scott invented the 'phonoautograph', the first device to record arbitrary sound in 1857. It used a membrane (which vibrated in response to sound) attched to a pen, which traced a line roughly corresponding to the sound wave form on to a moving roll of paper. Although able to record sound, the phonoautograph was unable to play back the recording; it was of little use other than as a laboratory curiousity.

The Phonograph and the Gramophone

The phonograph built expanding on the principles of the phonoautograph. Invented by Thomas Edison in 1877, the phonograph was a device with a cylinder covered with a soft material such as tin foil, lead, or wax on which a stylus drew grooves. The depth of the grooves made by the stylus corresponded to change in air pressure created by the original sound. The recording could be played back by tracing a needle through the groove and amplifying, through mechanical means, the resulting vibrations. A disadvantage of the early phonographs was the difficulty of reproducing the phonograph cylinders in mass production.

This changed with the advent of the gramophone (phonograph in American English), which was patented by Emile Berliner in 1887. The gramophone imprinted grooves on a disk record. Instead of recording the varying the depth of the groove (vertically), as with the phonograph, the vibration of the recording stylus was across the width of the track ( horizontally). The depth of the groove remained constant.

Early disc recordings and phonograph cylinders had about the same audio fidelity (despite the cylinder's theoretical advantages of constant linear groove speed and greater dynamic range of the hill-and-dale groove geometry). However, disc records were easier and cheaper to mass produce. From the beginning, the flat disks were easily mass-produced by a molding process, pressing a master image on a plate of shellac.

Originally, cylinders could only be copied by means of a pantograph mechanism, which was limited to making about twenty-five copies—all of significantly lower quality than the original—while simultaneously destroying the original. During a recording session, ten or more machines could be ranged around the talent to record multiple originals. Still, a single performance could produce only a few hundred salable copies, so performers were booked for marathon sessions in which they had to repeat their performances over and over again. By the mid-1900s, successful molding processes for cylinder recordings were developed, but by then disks had gained the ascendancy.

The speed at with the disks were rotated was eventually standardized at 78 rpm. Later innovations allowed lower rotations: 45 and 331/3 rpm, and the material was changed to vinyl.

Both phonograph cylinders and gramophone discs were played on mechanical devices most commonly hand wound with a clockwork motor. The sound was amplified by a cone that was attached to the diaphragm. The disc record largely supplanted the competing cylinder record by the late 1910s.

The advent of electrical recording in 1924 drastically improved the quality of the recording process of disc records. Oddly, there was a period of nearly five years, from 1925 to 1930, when the premiere technology for home sound reproduction consisted of a combination of electrically recorded records with the specially-developed Victor Orthophonic phonograph, a spring-wound acoustic phonograph which used waveguide engineering and a folded horn to provide a reasonably flat frequency response. Electrically-powered phonographs were introduced c. 1930, but crystal pickups and electronic reproduction did not become common until the late 1930s.

Magnetic Recording

Magnetic recording was demonstrated in principle as early as 1898 by Valdemar Poulsen in his telegraphone. Magnetic wire recording, and its successor, magnetic tape recording, involve the use of a magnetizable medium which moves with a constant speed past a recording head. An electrical signal, which is analogous to the sound that is to be recorded, is fed to the recording head, inducing a pattern of magnetization similar to the signal. A playback head can then pick up the changes in magnetic field from the tape and convert it into an electrical signal.

With the addition of electronic amplification developed by Curt Stille in the 1920s, the telegraphone evolved into wire recorders which were popular for voice recording and dictation during the 1940s and into the 1950s. The reproduction quality of wire recorders was low, however — significantly lower than that achievable with phonograph disk recording technology. Wire recorders could not prevent the wire from undergoing axial twisting, and hence could not insure that the wire was oriented the same way during recording and playback. When oriented the wrong way, high frequencies were reduced and the sound was muffled. The hysteresis of the steel material resulted in nonlinear transfer characteristics, manifesting as distortion. There were other practical difficulties, such as the tendency of the wire to become tangled or snarled. Splicing could be performed by knotting together the cut wire ends, but the results were not very satisfactory.

Early tape recorders were first developed in Germany. On Christmas day 1932 the British Broadcasting Corporation first used a tape recorder for their broadcasts.

Magnetic tape recording as we know it today was developed in Germany during the late 1930s by the C. Lorenz company. In 1938, S. J. Begun left Germany and joined Brush Development Company in the United States, where work continued but attracted little attention. During the war, the Allies became aware of radio broadcasts that seemed to be transcriptions, but whose audio quality was indistinguishable from that of a live broadcast. After the war, the Allied capture of a number of German Magnetophon recorders from Radio Luxembourg aroused great interest. These recorders incorporated all of the key technological features of analog magnetic recording, particular the use of high-frequency "bias."

Development of magnetic tape recorders in the late 1940s and early 1950s is associated with the Brush Development Corporation and its licensee, Ampex; the equally important development of magnetic tape media itself was led by Minnesota Mining and Manufacturing corporation (now known as 3M).

The use of magnetic tape recorders in broadcasting got a significant boost from Bing Crosby, who refused to perform on radio unless his shows could be prerecorded.

image:magtape1.jpg
7½" reel of ¼" recording tape
Typical of audiophile/consumer/educational use 1950s-60s

The typical professional tape recorder of the early 1950s used ¼" wide tape on 10½" reels, with a capacity of 2400 feet (731.5 metres). Typical speeds were initially 15 in/s (380 mm/s) yielding 30 minutes' recording time on a 2400 ft (730 m) reel. 30 in/s (720 mm/s) was used for the highest quality work.

Standard tape speeds varied by factors of two. 15 and 30 in/s were used for professional audio recording; 7½ in/s (190 mm/s) for home audiophile prerecorded tapes; 7½ and 3¾ in/s (190 and 95 mm/s) for audiophile and consumer recordings (typically on 7 in or 18 cm reels). 17/8; in/s (42 mm/s) and occasionally even 15/16 in/s (21 mm/s) were used for voice, dictation, and applications where very long recording times were needed, such as logging police and fire department calls.

The key electronic invention that made high-quality audio tape recording possible was the development of bias - a high-frequency signal, typically in the range of 50 to 150 kHz, which is added to the signal to be recorded before being applied to the recording head, such that the magnetization is performed at levels in the most nearly linear portion of the medium's transfer function.

A tape allows multiple tracks in parallel to each other. Because they are carried on the same medium, they stay in perfect synchronization. This allowed for stereo sound (2 tracks), and quadrophonic sound (4 tracks). In a professional setting today, such as a studio, audio engineers may use 24 tracks or more for their recordings, one (or more) tracks for every instrument played.

Magnetic audio tape can be easily and inaudibly spliced. The combination of the ability to edit via splicing, and the ability to record multiple tracks, revolutionized studio recording. It became common studio recording practice to record on multiple tracks, and mix down afterwards. The convenience of tape editing and multitrack recording led to the rapid adoption of magnetic tape as the primary technology for commercial musical recordings. Although 331/3; rpm and 45 rpm vinyl records were the dominant consumer format, recordings were customarily made first on tape, then transferred to disk.

Analog magnetic tape recording introduces noise, usually called "hiss", caused by the finite size of the magnetic particles in the tape. There is a direct tradeoff between noise and economics. Signal-to-noise ratio is reduced at higher speeds and with wider tracks, increased at lower speeds and with narrower tracks.

By the late 1960s, disk reproducing equipment became so good that audiophiles soon became aware that some of the noise audible on recordings was not surface noise or deficiencies in their equipment, but reproduced tape hiss. A few companies starting making "direct to disk" specialty recordings, made by feeding microphone signals directly to a disk cutter (after amplification and mixing). These recordings never became popular, but they dramatically demonstrated the magnitude and importance of the tape hiss problem.

Prior to 1963, when Philips introduced the Compact audio cassette, almost all tape recording had used the reel-to-reel (also called "open reel") format. Previous attempts package the tape in a convenient cassette that required no threading met with limited success; the most successful was 8-Track cartridge used primarily in automobiles for playback only. The Philips Compact audio cassette added much needed convenience to the tape recording format and quickly came to dominate the consumer market, although it was lower in quality than open reel formats.

In the 1970s, advances in solid-state electronics made the design and marketing of more sophisticated analog circuitry economically feasible. This led to a number of attempts to reduce tape hiss through the use of various forms of volume compression and expansion, the most notable and commercially successful being several systems developed by Dolby Laboratories. These systems divided the frequency spectrum into multiple bands and applied volume compression/expansion independently to each band. The Dolby systems were very successful at increasing the effective dynamic range and signal-to-noise ratio of analog audio recording; to all intents and purposes, audible tape hiss could be eliminated. The original Dolby A was only used in professional recording. Successors found use in both professional and consumer formats; Dolby B became almost universal for the compact cassette, both prerecorded and for home use.

In the 1980s, digital recording methods were introduced, and analog tape recording was gradually displaced. Digital audio tape never became important as a consumer recording medium partially because of legal complications arising from piracy fears on the part of the record companies. They had opposed magnetic tape recording when it first became available to consumers, but the technical difficulty of juggling recording levels, overload distortion, and residual tape hiss was sufficiently high that magnetic tape piracy never became an unsurmountable commercial problem. With digital methods, copies of recordings could be exact, and piracy might have become a serious commercial problem. The instroduction of the audio CD occurred about the same time and may have had the effect of reducing the need for a better recording medium. Digital tape is still used in professional situations and the DAT variant has found a home in computer data backup applications.

Recording on Film

The first attempts to record sound to an optical medium occurred around 1900. In 1906 Lauste applied for a patent to record sound on film, but was ahead of his time. In 1923 de Forest applied for a patent to record to film. In 1927 the sound film The Jazz Singer was released; while not the first, it made a tremendous hit and made the public and the film industry realize that sound film was more than a mere novelty.

The Jazz Singer used a process called Vitaphone, a process that involved synchronizing the projected film to sound recorded on disk. It essentially amounted to playing a phonograph record, but one that was recorded with the best electronic technology of the time. Audiences used to acoustic phonographs and recordings would, in the theatre, have heard something resembling 1950s "high fidelity."

In the days of analog technology, however, no process involving a separate disk could hold synchronization precisely or reliably. Vitaphone was quickly supplanted by technologies which recorded a sound track optically directly onto the side of the strip of motion picture film. This was the dominant technology from the 1930s through the 1960s and is still in use as of 2004.

There are two primary methods for optical recording on film. Variable density recording uses changes in the darkness of the soundtrack side of the film to represent the soundwave. Variable width recording uses changes in the width of a dark strip to represent the soundwave.

In both cases light that is sent through the part of the film that corresponds to the soundtrack changes in intensity, proportional to the original sound, and that light is not projected on the screen but converted into an electrical signal by a light sensitive device.

In the late 1950s the cinema industry, desperate to provide a theatre experience that would be overwhelmingly superior to television, introduced wide-screen processes such as Cinerama, Todd-AO, and CinemaScope. These processes at the same time introduced technical improvements in sound, generally involving the use of multitrack magnetic sound, recorded on an oxide stripe laminated onto the film. In subsequent decades, a gradual evolution occurred with more and more theatres installing various forms of magnetic-sound equipment.

In the 1990s, digital systems were introduced and began to prevail. Ironically, in many of them the sound recording is, as in Vitaphone, again recorded on a separate disk; but now, digital processes can achieve reliable and perfect synchronization.

Digital Recording

Early digital audio recorders use a device to make it possible to record digital audio on a U-matic video machine. This was followed by digital open reel multitrack recorders. With the improvement in digital storage technology, a variety of recording media is used to record digital audio today.

Digital Audio Tape (DAT) recorded the raw audio sampled at 48 kHz with a resolution of 16 bits. DAT is still used in studios. A failed digital tape recording system is the Digital Compact Cassette (DCC).

In the consumer market, tapes and gramophones were largely displaced by the compact disc (CD) and a lesser extent the minidisc. These recording media are fully digital and require complex electronics to play back.

Sound files can be stored on any computer storage medium.

As hard disk capacities and computer CPU speeds increased at the end of the 1990s, hard disk recording became more popular.

Technique

The earliest methods of recording sound involved the live recording of the performance directly to the recording medium. This was an entirely mechanical process, often called "Acoustical recording". The sound of the performers was captured by a diaphragm with the cutting needle connect to it. The needle made the grooves in the recording medium.

To make this process as efficient as possible the diaphragm was located at the apex of a cone and the performer(s) would crowd around the other end. If a performer was too loud then they would need to move back from the mouth of the cone to avoid drowning out the other performers. As a result of this, in early Jazz recordings a block of wood was used in place of the bass drum.

The advent of electrical recording made it possible to use microphones to capture the sound of the performance. The leading record labels switched to the electric microphone process in 1925, and most other record companies followed their lead by the end of the decade. Electrical recording increased the flexibity and sound quality. However once the performance was still cut to the recording medium, so if a mistake was made the recording was useless.

Electrical recording made it possible to record one part to disc and then play that back while playing another part, recording both parts to a second disc. This is called over-dubbing. The first commercially issued records using over-dubbing were released by the Victor Talking Machine Company in the late 1920s. However overdubbing was of limited use until the advent of analogue audio tape. Use of tape overdubbing was pioneered by Les Paul and is called 'sound on sound' recording. Studios thus could create recorded "performances" that could not be duplicated by the same artists performing live.

The analogue tape recorder made it possible to erase or record over a previous recording so that mistakes could be fixed. Another advantage of recording on tape is the ability to cut the tape and join it back together. This allows the recording to be edited. Pieces of the recording can be removed, or rearranged. See Audio editing, Audio mixing.

Mention Multitrack Recording here.

The advent of electronic instruments (especially keyboardss and synthesisers), effects and other instruments has lead to the importance of MIDI in recording. For example, using MIDI timecode, it is possible to have different equipment 'trigger' without direct human intervention at the time of recording.

In more recent times, computers (digital audio workstation) have found an increasing role in the recording studio, as their use eases the tasks of cutting and looping, as well as allowing for instantaneous changes, such as duplication of parts, the addition of affects and the rearranging of parts of the recording.

See also: binaural recording, microphone technique, List of audio formats.