The earliest methods of recording arbitrary sounds 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 connected to it. The needle made the groove in the recording medium. To make this process as efficient as possible the diaphragm was located at the apex of a cone and the performers 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. In some early jazz recordings a block of wood was used in place of the bass drum.
Main article: Phonautograph
In 1857, édouard-Léon Scott de Martinville invented the phonautograph, the first device that could record sound waves as they passed through the air. It was intended only for visual study of the recording and could not play back the sound. The recording medium was a sheet of soot-coated paper wrapped around a rotating cylinder carried on a threaded rod. A stylus, attached to a diaphragm through a series of levers, traced a line through the soot, creating a graphic record of the motions of the diaphragm as it was minutely propelled back and forth by the audio-frequency variations in air pressure.
In the spring of 1877 another inventor, Charles Cros, suggested that the process could be reversed by using photoengraving to convert the traced line into a groove that would guide the stylus, causing the original stylus vibrations to be recreated, passed on to the linked diaphragm, and sent back into the air as sound. An invention from America soon eclipsed this idea, and it was not until 1887 that yet another inventor, Emile Berliner, actually photoengraved a phonautograph recording into metal and played it back.
Scott’s early recordings languished in French archives until 2008, when scholars keen to resurrect the sounds captured in these and other types of early experimental recordings tracked them down. Rather than using rough 19th century technology to create playable versions, they were scanned into a computer and software was used to convert their sound-modulated traces into digital audio files. Brief excerpts from two French songs and a recitation in Italian, all recorded in 1860, are the most substantial results.
Edison’s cylinder-based Phonograph
The phonograph expanded on the principles of the phonautograph. Perfected by Thomas Edison in 1878, the phonograph was a device with a cylinder covered with an impressionable material such as tin foil, lead, or wax on which a stylus etched 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.
The disk-based gramophone
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 the flat side of a disc rather than the outside of a cylinder. Instead of recording by 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. Berliner called this audio disc a “gramophone record”, although it was often called a “phonograph record” in U.S. English.
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 direct 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 1902, successful molding processes for cylinder recordings were developed.
The speed at which the disks were rotated was eventually standardized at 78 rpm. Later innovations allowed lower rotations: 45, 33? and as slow as 16 rpm for broadcast transcriptions and some rare consumer recordings. The material used was eventually 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 fell into public favour quickly, and cylinders were not produced after 1929. The advent of electrical recording in 1925 drastically improved the quality of the recording process of disc records. There was a period of nearly five years, from 1925 to 1930, when the premier 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 wave-guide engineering and a folded horn to provide a reasonably flat frequency response. Electrically powered phonographs were introduced c. 1930, but crystal pick-ups and electronic reproduction did not become common until the late 1930s.
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 flexibility of the process and the sound quality of the recordings. However, the performance was still cut directly to the recording medium, so if a mistake was made the recording was useless.
Electrical recording made it more feasible to record one part to disc and then play that back while playing another part, recording both parts to a second disc. This and conceptually related techniques, known as over-dubbing, enable studios to create recorded “performances” that feature one or more artists each singing multiple parts or playing multiple instrument parts and that therefore could not be duplicated by the same artist or artists performing live. 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.
Main article: 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 magnetized 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 significantly lower than that achievable with phonograph disk recording technology. There were also 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.
On Christmas Day, 1932 the British Broadcasting Corporation first used a steel tape recorder for their broadcasts. The device used was a Marconi-Stille recorder, a huge and dangerous machine which used steel razor tape 3 mm (0.1″) wide and 0.08 mm (0.003″) thick running at 90 metres per minute (approximately 300 feet per minute) past the recording and reproducing heads. This meant that the length of tape required for a half-hour programme was nearly 3 kilometres (1.9 mi) and a full reel weighed 25 kg (55 pounds).
Main article: Magnetic tape sound recording
7″ reel of ?” recording tape, typical of audiophile, consumer and educational use in the 1950s–60s
Engineers at AEG, working with the chemical giant IG Farben, created the world’s first practical magnetic tape recorder, the ‘K1’, which was first demonstrated in 1935. During World War II, an engineer at the Reichs-Rundfunk-Gesellschaft discovered the AC biasing technique. With this technique, an inaudible high-frequency signal, typically in the range of 50 to 150 kHz, is added to the audio signal before being applied to the recording head. Biasing radically improved the sound quality of magnetic tape recordings. By 1943 AEG had developed stereo tape recorders.
During the war, the Allies became aware of radio broadcasts that seemed to be transcriptions (much of this due to the work of Richard H. Ranger), but their audio quality was indistinguishable from that of a live broadcast and their duration was far longer than was possible with 78 rpm discs. At the end of the war, the Allied captured a number of German Magnetophon recorders from Radio Luxembourg that aroused great interest. These recorders incorporated all of the key technological features of analogue magnetic recording, particularly the use of high-frequency “bias”.
Development of magnetic tape recorders in the late 1940s and early 1950s is associated with the Brush Development Company 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).
American audio engineer John T. Mullin and entertainer Bing Crosby were key players in the commercial development of magnetic tape. Mullin served in the U.S. Army Signal Corps and was posted to Paris in the final months of World War II; his unit was assigned to find out everything they could about German radio and electronics, including the investigation of claims that the Germans had been experimenting with high-energy directed radio beams as a means of disabling the electrical systems of aircraft. Mullin’s unit soon amassed a collection of hundreds of low-quality magnetic dictating machines, but it was a chance visit to a studio at Bad Neuheim near Frankfurt while investigating radio beam rumours that yielded the real prize.
Mullin was given two suitcase-sized AEG ‘Magnetophon’ high-fidelity recorders and fifty reels of recording tape. He had them shipped home and over the next two years he worked on the machines constantly, modifying them and improving their performance. His major aim was to interest Hollywood studios in using magnetic tape for movie soundtrack recording.
Mullin gave two public demonstrations of his machines, and they caused a sensation among American audio professionals—many listeners literally could not believe that what they were hearing was not a live performance. By luck, Mullin’s second demonstration was held at MGM studios in Hollywood and in the audience that day was Bing Crosby’s technical director, Murdo Mackenzie. He arranged for Mullin to meet Crosby and in June 1947 he gave Crosby a private demonstration of his magnetic tape recorders.
Crosby was stunned by the amazing sound quality and instantly saw the huge commercial potential of the new machines. Live music was the standard for American radio at the time and the major radio networks did not permit the use of disc recording in many programs because of their comparatively poor sound quality. But Crosby disliked the regimentation of live broadcasts, preferring the relaxed atmosphere of the recording studio. He had asked NBC to let him pre-record his 1944–45 series on transcription discs, but the network refused, so Crosby had withdrawn from live radio for a year, returning for the 1946–47 season only reluctantly.
Mullin’s tape recorder came along at precisely the right moment. Crosby realised that the new technology would enable him to pre-record his radio show with a sound quality that equaled live broadcasts, and that these tapes could be replayed many times with no appreciable loss of quality. Mullin was asked to tape one show as a test and was immediately hired as Crosby’s chief engineer to pre-record the rest of the series.
Crosby became the first major American music star to use tape to pre-record radio broadcasts, and the first to master commercial recordings on tape. The taped Crosby radio shows were painstakingly edited through tape-splicing to give them a pace and flow that was wholly unprecedented in radio. Mullin even claims to have been the first to use “canned laughter”; at the insistence of Crosby’s head writer, Bill Morrow, he inserted a segment of raucous laughter from an earlier show into a joke in a later show that had not worked well.
Keen to make use of the new recorders as soon as possible, Crosby invested $50,000 of his own money into Ampex, and the tiny six-man concern soon became the world leader in the development of tape recording, revolutionising radio and recording with its famous Model 200 tape deck, issued in 1948 and developed directly from Mullin’s modified Magnetophones.
Main article: Multitrack recording
The next major development in magnetic tape was multitrack recording, in which the tape is divided into multiple tracks parallel with each other. Because they are carried on the same medium, the tracks stay in perfect synchronization. The first development in multitracking was stereo sound, which divided the recording head into two tracks. First developed by German audio engineers ca. 1943, 2-track recording was rapidly adopted for modern music in the 1950s because it enabled signals from two or more separate microphones to be recorded simultaneously, enabling stereophonic recordings to be made and edited conveniently. (The first stereo recordings, on disks, had been made in the 1930s, but were never issued commercially.) Stereo (either true, two-microphone stereo or multimixed) quickly became the norm for commercial classical recordings and radio broadcasts, although many pop music and jazz recordings continued to be issued in monophonic sound until the mid-1960s.
Much of the credit for the development of multitrack recording goes to guitarist, composer and technician Les Paul, who also helped design the famous electric guitar that bears his name. His experiments with tapes and recorders in the early 1950s led him to order the first custom-built eight-track recorder from Ampex, and his pioneering recordings with his then wife, singer Mary Ford, were the first to make use of the technique of multitracking to record separate elements of a musical piece asynchronously — that is, separate elements could be recorded at different times. Paul’s technique enabled him to listen to the tracks he had already taped and record new parts in time alongside them.
Multitrack recording was immediately taken up in a limited way by Ampex, who soon produced a commercial 3-track recorder. These proved extremely useful for popular music, since they enabled backing music to be recorded on two tracks (either to allow the overdubbing of separate parts, or to create a full stereo backing track) while the third track was reserved for the lead vocalist. Three-track recorders remained in widespread commercial use until the mid-1960s and many famous pop recordings — including many of Phil Spector’s so-called “Wall of Sound” productions and early Motown hits — were taped on Ampex 3-track recorders. Engineer Tom Dowd was among the first to use multitrack recording for popular music production while working for Atlantic Records during the 1950s.
The next important development was 4-track recording. The advent of this improved system gave recording engineers and musicians vastly greater flexibility for recording and overdubbing, and 4-track was the studio standard for most of the later 1960s. Many of the most famous recordings by The Beatles and The Rolling Stones were recorded on 4-track, and the engineers at London’s Abbey Road Studios became particularly adept at a technique called “reduction mixes” in the UK and “bouncing down” in the United States, in which several tracks were recorded onto one 4-track machine and then mixed together and transferred (bounced down) to one track of a second 4-track machine. In this way, it was possible to record literally dozens of separate tracks and combine them into finished recordings of great complexity.
All of the Beatles classic mid-1960s recordings, including the albums Revolver and Sgt Pepper’s Lonely Hearts Club Band, were recorded in this way. There were limitations, however, because of the build-up of noise during the bouncing-down process, and the Abbey Road engineers are still famed for their ability to create dense multitrack recordings while keeping background noise to a minimum.
4-track tape also enabled the development of quadraphonic sound, in which each of the four tracks was used to simulate a complete 360-degree surround sound. A number of albums were released both in stereo and quadrophonic format in the 1970s, but ‘quad’ failed to gain wide commercial acceptance. Although it is now considered a gimmick, it was the direct precursor of the surround sound technology that has become standard in many modern home theatre systems.
In a professional setting today, such as a studio, audio engineers may use 24 tracks or more for their recordings, using one or more tracks for each instrument played.
The combination of the ability to edit via tape splicing and the ability to record multiple tracks revolutionized studio recording. It became common studio recording practice to record on multiple tracks, and bounce down afterward. 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 33? rpm and 45 rpm vinyl records were the dominant consumer format, recordings were customarily made first on tape, then transferred to disc, with Bing Crosby leading the way in the adoption of this method in the United States.
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 increased at higher speeds and with wider tracks, and decreased 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 specialist companies started making “direct to disk” specialty recordings, made by feeding microphone signals directly to a disk cutter (after amplification and mixing), in essence reverting to the pre-War direct method of recording. These recordings never became popular, but they dramatically demonstrated the magnitude and importance of the tape hiss problem.
Before 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 to 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 a decade or so later had begun to dominate the consumer market, although it was to remain 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 several bands and applied volume compression/expansion independently to each band (Engineers now often use the term “compansion” to refer to this process). 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 prerecorded music on compact cassette. Subsequent forms, including Dolby C, (and the short-lived Dolby S) were developed for home use.
In the 1980s, digital recording methods were introduced, and analog tape recording was gradually displaced, although it has not disappeared by any means. (Many professional studios, particularly those catering to big-budget clients, use analog recorders for multitracking and/or mixdown.) Digital audio tape never became important as a consumer recording medium partially due to 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 insurmountable commercial problem. With digital methods, copies of recordings could be exact, and piracy might have become a serious commercial problem. Digital tape is still used in professional situations and the DAT variant has found a home in computer data backup applications. Many professional and home recordists now use hard-disk-based systems for recording, burning the final mixes to recordable CDs (CD-R’s).
Most Police forces in the United Kingdom (and elsewhere) still use analogue compact cassette systems to record Police Interviews as it provides a medium less prone to accusations of tampering.