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Alan Dower Blumlein (29 June 1903 — 7 June 1942) was a British electrical and electronics engineer and inventor in the fields of telephony, sound recording and reproduction, television and radiolocation. A long-term leading designer at EMI, Blumlein co-authored the British 405-line television standard; he designed the first BBC Television center at Alexandra Palace and supervised its construction and initial operation. During World War II Blumlein designed ground and airborne radars, and was killed in an air crash testing the prototype of the H2S radar.

In seventeen years of professional work Blumlein patented 128 inventions, including matrix processing of stereophonic sound, Blumlein stereo microphones, the Blumlein transmission line, the ultralinear valve stage, the Miller integrator, the transversal filter, and the slot antenna. Blumlein expanded on the theory of operation, and developed practical applications of basic electronic building blocks: the cathode follower, the long-tailed pair, and the negative-feedback amplifier. His works laid the foundation of analogue television, shaping and processing of radar and video signals, and the first generation of British computers. Blumlein is popularly credited as "the father of stereo" for his 1931 invention of the 45/45 phonograph recording principle that became the worldwide standard for stereo LP records in the late 1950s.

Early years
Alan's father, businessman Semmy Blumlein (1863—1914), was born to an affluent family of Bavarian Jews. After a brief apprenticeship in Liverpool, eighteen-year-old Semmy left to seek fortune in South Africa. By 1883 he was firmly landed in Kokstad, were he met the family of Presbyterian Scottish missionary William Dower. In 1889 Semmy married the preacher's elder daughter Jessie Dower. The outbreak of the Second Boer War forced the Blumleins to repatriate from Pretoria to London. Semmy Blumlein, now a prosperous banker and a board member of international corporations, could afford renting a spacious house in Hampstead and employ a housemaid, a cook and a nurse. Alan Blumlein, the second child in the family, was born in the family house at 31 Netherhall Gardens on 29 June 1903.

Alan attended private preparatory schools since the age of six. He was proficient in arithmetics, less so in reading; his often quoted statement that "he could not read at twelve but he knew a lot about quadratic equations" is merely a joke that should not be taken literally. His reading skills were rated as good but, as Blumlein later recalled, literature and especially poetry were completely alien to him. Even worse, he could not master English orthography. His mother tried enrolling Alan to different country schools and crammers, to no avail. However, at the onset of World War I Blumlein experienced a series of emotional shocks that changed his attitude towards learning. On 28 July 1914 (the day when Austria declared war on Serbia) Alan's father suddenly died, leaving the family a modest fortune but no long-term sources of income. After Britain's entry into the war schoolmates started harassing Alan for his "German" surname. In January 1915 mother sent Alan to Ovingdean Hall School, in hope that the cram school environment will improve spelling. It is likely that by now Blumlein himself realized that he must overcome dysgraphia. In twenty months at Ovingdean he somehow managed to master the basics of spelling. Spelling errors persisted throughout his life; Blumlein's last letter, written two days before his death, contains "only" nine errors over two handwritten pages.

In 1916 mother placed Blumlein at Highgate School, which she thought was more appropriate for a career in technology than prestigious classical schools. In 1921 Alan enrolled at the City and Guilds Engineering College. Owing to excellent preparation at Highgate he was admitted directly into the second year of the electrical engineering program and won one of six available tuition scholarships.. Blumlein completed the remaining three-year program in two years, and received his first class Bachelor of Engineering degree from the University of London at the age of twenty. By this time he decided to concentrate on the emerging electronics, rather than traditional electrical engineering. Instead of postgraduate education, which was almost nonexistent at City and Guilds, he applied for the salaried position of an assistant demonstrator, attached to professor Edward Mallett in running the course on "Wireless telegraphy and telephony". Working with Mallett, Blumlein learnt the fundamentals of electronics, published his first journal article, received his first award for research, and made useful connections in academia. Many students of professor Mallett will later become Blumlein's associates at EMI.

Very soon Mallett realized that Blumlein had outgrown the modest capacity of City and Guilds, and will be better off gain gaining practical experience in the industry. He put Blumlein in contact with International Western Electric Company (IWE), then a division of Western Electric that became the independent International Standard Electric Corporation (ISEC) later in 1925. The company denied employment to Jews, but Mallett succeeded in pushing the promising applicant through corporate bureaucracy. In September 1924 Blumlein was hired to the position of Telephone Engineer at the IWE Transmission Laboratory, with a substantial annual salary. At first, he performed various unrelated minor tasks, from measuring properties of novel permalloys to checking his colleagues' hearing with the Wente condenser microphone and drawing averaged audiograms. Blumlein was the first person to integrate a high-impedance microphone and a preamplifier into a single package that could easily drive long, high-capacitance cables. Western Electric published the first description of a similar device later, in 1928; it it not known whether the Americans used Blumlein's idea or not.

Work in telephony (1925–1929)
In February 1925 Blumlein was transferred to a workgroup engaged in electromagnetic interference tests and acceptance testing on long distance telephone lines in continental Europe. The industry was on the rise due to post-war economic growth in general, and the recent standardization of national telephone networks. European telephone lines were usually laid along existing overhead power lines and electrified railroads, thus interference was always an issue.. Blumlein spent most on 19251927 in France and Switzerland, inspecting newly built ISEC lines. In March 1927 Blumlein patented his first invention (jointly with J. P. Jones) a low-crosstalk loading coil for long-distance lines, and afterwards developed the appropriate production technology. The Blumlein coil went into production immediately and was used for the first time in the new Winterthur-Schaffhausen line. After it passed acceptance test, Blumlein spent the winter of 19271928 inspecting the AltdorfGotthard line, where cables were subjected to alpine climate as well as severe interference from the Gotthard railway. Here, in December 1927, he invented the impedance bridge for balancing long-distance lines. The Blumlein bridge, employing a centre-tapped coil, was by design far better balanced than the purely resistive Wheatstone bridge. The invention revolutionized the measurement of resistance, inductance and capacitance. For decades, the Blumlein bridge was the most precise measurement instrument available, and it also cheap and easy to use.

In 1928 Blumlein left the ISEC and joined Standard Telephones and Cables (STC) to work on "more confidential problems", probably related to submarine communications cables. The nature of this work may only be inferred indirectly, from the context of his inventions patented in 19291930.

EMI recording system (1930–1931)


In 1925 the London-based Columbia Graphophone Company licensed the use of the Maxfield-Harrison recording technology from Western Electric. Royalty expense of one pence per each stamped phonograph record was deemed too high, so the company's technical director Isaac Shoenberg decided to develop its own technology, which had to be completely independent of the existing American patents. The first moving iron record cutter developed at Columbia suffered from excessive distortion. By the standards of the 1920s it was barely adequate for recording European music, but completely unusable for traditional Japanese music. The Columbia headhunters identified three STC engineers, including Blumlein, as the men who could do the job right, and in March 1929 Shoenberg hired Blumlein. Leaving the STC was a wise decision: although the company eventually survived the Great Depression, Blumlein's department at the STC did not.

Blumlein realized that his predecessors at Columbia were on the wrong path from the start. High distortion is typical for all moving iron devices; an audio recorder should employ a fundamentally more linear moving coil drive. Moving coil systems do not need mechanical dampers, which were the essence of the Maxfield-Harrison patent. Instead, the damping torque is produced by the counter-electromotive force in a uniform magnetic field. The force is inherently linear, and the system as whole is predictable and designable. A moving coil device can reliably calculated and engineered with the help of classical electromagnetism theory.

By October 1929 Blumlein produced the drafts and analysis of his first record cutter. The key element, a lightweight single-turn moving coil, had to be milled from a solid aluminium piece; in theory it enabled bandwidth up to $15 kHz$, although in practice bandwidth was deliberately with mechanical adjustments and electrical shunts. The first prototype suffered from unacceptably high losses in its field system. Blumlein redesigned the cutter with the help of Henry 'Ham' Clark and Herbert Holman; the final production version was patented by Blumlein and Holman in March 1930. Then Blumlein, Holman and Clark developed and patented the HB-1A (Holman-Blumlein) dynamic microphone. The complete set of recording equipment was built and tested in six months, and was by design superior to the Maxfield-Harrison system.

Test recording commenced in January 1931; a few weeks later Columbia and The Gramophone Company merged into EMI. Reorganization delayed deployment of new equipment, which was installed in yet unfininished EMI Recording Studios in September 1931. Blumlein's set won comparative tests over the Maxfield-Harrison system. In July 1932 all divisions of EMI were upgraded with new equipment; by mid-1930s the EMI recording system became de-facto national standard. It saw heavy use until the outbreak of World War II, and some sets operated into the 1960s. The Holman-Blumlein microphones were employed by the EMI from 1931 to 1955; they defined the excellent sonic quality of EMI coarsegroove piano recordings.

Stereophonic sound (1930–1935)
Binaural transmission and reproduction of sound was dates back to the 1881 invention of the Théâtrophone by Clément Ader. In the 1910s, audio power amplifiers made possible reproduction of binaural signals through loudspeakers, however all experiments were unsuccessful. Loudspeakers could not recreate spatial imaging that was preserved by stereo headphones. In 1930–1931 Arthur C. Keller, Harvey Fletcher and Alan Blumlein, acting independently, resumed research of stereophonic sound. There is no evidence that Blumlein was aware of the American research, and vice versa. The issue of "who was the first" in the development of stereo has no definite answer. The three inventors, acting independently, had different objectives and developed significantly different solutions.

Keller was interested in public address sound. He tried to capture the "acoustic front" radiated by an orchestra with an array of microphones, and reproduce it in a remote listening hall via a matching array of loudspeakers. The minimal working configuration contained three parallel channels, and according to Fletcher it recreated spatial images "fairly accurately in breadth, and to a reasonable degree in depth". A two-channel system was a failure: the sound invariably fell apart into two isolated sources with a hole in the middle. Fletcher and Blumlein took a different path; instead of imitating sound radiated by the sources, they focused on the sound that reaches the listener's ears. Binaural recording needs only two microphones that emulate human ears. However, if the sound is registered with pressure microphones, which were then prevalent, it can only be reproduced via headphones, but not loudspeakers. The differences in phase between the signals that reach the listener's ears, which are critical for sound localization, cancel each other out in the space between the listener and the speakers. To solve the problem, Blumlein suggested converting phase differences of the original signal into level differences. If phase differences indicate that the virtual sound source should be placed on the left, the system should increase the level of the left channel and decrease the level of the right right channel, and vice versa. This manipulation, called the Blumlein shuffling, is performed with an electronic Blumlein shuffler – a device that redistributes energy between the two channels in a manner similar to how the Dolby Surround processor redistributes energy into the centre channel. The analogy is not coincidental because the Dolby systems use the same matrix processing approach as was proposed by Blumlein in 1931.

Very little is known about Blumlein's work on stereo sound until 14 December 1931, when he filed an application for what would become the United Kingdom patent 394325 - the fundamental, seminal work on stereophonic sound. 24 pages of the patent contained a brief explanation of underlying psychoacoustics, a roadmap for the introduction of surround sound in film industry, and no less than 70 claims. Blumlein proposed new stereo microphone configurations (the Blumlein pair), stereo optical sound recording technique, and the use of cellulose acetate for mastering of phonograph records. The best known, and probably the most important proposal was the 45/45 stereo phonograph recording system. Unlike the earlier 0/90 system, the cutter for the 45/45 system is fully symmetrical, with left and right actuators placed at exactly 45° and –45° to the vertical axis. The resulting record is backward compatible with monaural lateral pickups.

In 1933 Blumlein's workgroup designed and built the stereo recording set; the first ten 45/45 stereo records were cut in December. Keller recorded his stereo records earlier, but he used the dual-groove system that was ill-suited for mass production. On 19 January 1934 Abbey Road Studios made the first stereo recordings of the London Symphony Orchestra conducted by Thomas Beecham. In the summer of 1935 Blumlein created a series of set and location shorts with stereo sound synchronously recorded to an optical soundtrack. Technical feasibility of stereo recording was proven, but neither the market nor the industry were ready for it. EMI director Louis Sterling believed that stereo sound in film would only become viable after the introduction of colour. Likewise, the phonograph industry had to replace noisy shellac records with a high fidelity, long-play medium. EMI and their American competitors suspended research into stereo until the 1950s.

In 1957, when stereo LPs became economically and technologically viable, the 45/45 system was reinvented by Decca Records in the United Kingdom and by Westrex (a company spun off Western Electric) in the United States. While Decca recognized Blumlein's priority, Westrex did not. The Recording Industry Association of America endorsed the Westrex System as the national standard, causing public outrage in Britain and a campaign for reinstating Blumlein's priority in the United States. By the end of 1958 the Americans accepted the facts, the Westrex patent was effectively voided and the 45/45 system became a worlwide free standard

Television (1933–1939)


The Gramophone Company began developing electronic television in 1929; after the 1931 merger with Columbia Graphophone television became the main strategic goal of the newly formed EMI. In March 1933 Blumlein effectively became the television project manager, with substantial research budget and a roving commission. The next year became probably the most productive for Blumlein, and a year of exceptional progress for the television in general. In Germany, Fernseh AG and Telefunken had developed the 180-line television system, which would begin regular broadcasts in 1935. In the United States, Vladimir Zworykin was perfecting his fully electronic 343-line system at RCA. Philo Farnsworth, the maverick competitor to RCA, was consulting the Germans and the British. The RCA initially opposed television research at the EMI (which was 27% owned by RCA until the middle of 1934), but by 1933 relationships improved. The Americans regularly informed the British about the progress of Zworykin's work, and delivered samples of his imaging tube to the EMI. However, these early versions of the iconoscope were not fit for broadcast service yet. Zworykin, it seemed, was facing unsurmountable technical problems, and would not divulge the already found solutions.

Shoenberg made a decision to develop the imaging tube in-house, independently of RCA. He hired a group of promising young physicists from the Oxford and Cambridge universities, and assigned Blumlein the task of integrating newcomers into the business environment. In January 1934 a workgroup led by Cambridge PhD James Dwyer McGee produced the first viable imaging tube, the emitron. The first emitrons, just like Zworykin's iconoscopes, sufferred from high perspective distortion and excessive spurious signals caused by uncontained secondary emission. Blumlein, Brown and White solved the latter problem electronically, via addition of "tilt and bend" signals to the output of the imaging tube. The ultimate solution, decelerating electron beams via cathode potential stabilisation (c.p.s.), was invented by Blumlein and McGee independently, and was patented by them jointly in July 1934. In September 1934 Blumlein patented two of his major inventions related to television - the cathode follower and the DC restoration technology.

Blumlein spent most of the second half of 1934 in negotiations within the Television Advisory Committee chaired by Lord Selsdon. Blumlein proposed and substantiated the key elements of the future broadcasting standard: 5:4 aspect ratio, transmission of d.c. components of the source video signal, positive amplitude modulation, frame rate of 50 interlaced half-frames per second, with 405 lines per frame (twice as much as Blumlein himself contemplated in the beginning of 1934). Bandwidth of composite video signal increased to unprecedented $2.4 MHz$. Shoenberg was uncertain about Blumlein's bold proposals, but in February 1935 he agreed, and persuaded the Committee to approve them.

In 19351936 Blumlein supervised design and construction of the BBC Television centre and transmitter at Alexandra Palace. Nine of seventeen patents that were essential to the operation of the Television Centre were authored by Blumlein. Overall, in six years of working on television (19331939) Blumlein authored 75 patents in various areas of electronics and technology, from glassblowing to special video effects. The list includes such important building blocks as the cathode follower, the long-tailed pair and the negative-feedback amplifier.

On 2 November 1936 the Alexandra Palace transmitter commenced test broadcasts. The rival mechanical television developed by John Logie Baird was broadcasting from Crystal Palace. On 30 November the latter was destroyed by fire; regardless of the accident, the authorities had already made the decision in favor of the Marconi-EMI system, which was announced on 4 February 1937. Baird's system was rejected; the Marconi-EMI 405-line television system, also called the Blumlein waveform, became a national standard in 1937 and remained in place until 1986. The Americans appreciated the benefits of the Blumlein waveform, and integrated its elements into their own standards. The RCA waveform, adopted in June 1938, was following the Marconi-EMI system apart from a higher line count and a different aspect ratio. The television technology market became a duopoly of RCA and the Marconi-EMI alliance. French, German, Japanese and Soviet researchers abandoned their indigenous projects and adopted the British or American standards.

From December 1936 the Alexandra Palace tower was transmitting scheduled studio programmes, film transfers and live outside broadcasts. The most outstanding show of the period was the live report of the Coronation procession on 12 May 1937, watched by more than 50000 viewers. Well before the event, Shoenberg requested Blumlein to design wideband balanced video cables for transmitting signals from remote cameras to the Broadcasting House and from there to Alexandra Palace.. In due time, the Blumlein team laid a network of undeground cables, broadcasting vans and repeaters. Once the system was tested live, the BBC extended the scope of live coverage to current politics and major sports events. The authorities approved construction of four additional regional stations, each having four times the power of the London transmitter; this project, scheduled for 1941-1944, was cancelled with the outbreak of World War II.

Radiolocation (1939–1942)
In the end of 1938 the EMI was awarded a contract for the manufacture of Mark VIII anti-aircraft sound locator. The operation of sound locator depended on the hearing and skills of its human operator. Blumlein suggested augmenting the acoustic channel with Visual Indicating Equipment (VIE) that used an electronic stereo shuffler to convert phase differences to level differences. The VIE then extracted information on the bearing and elevation of the sound source, and displayed them on two cathode ray tubes. The VIE was immediately rushed into production, retrofitted to existing sound locators, and remained in active use until the deployment of anti-aircraft gun-laying radars.

With the outbreak of World War II Blumlein applied the same stereo technique to long-range early warning radars. In the end of 1939 the EMI began tests of an experimental radar operating at $66 MHz$. In the first half of 1940 Blumlein invented and patented new techniques for shaping, detecting and selecting electromagnetic pulses, and submitted the drafts for enhancing the Chain Home system with early warning Doppler radars operating at $60 MHz$. However, the Battle of Britain shifted priorities in favor of air inteception (AI), ground-controlled interception (GCI) and gun-laying (GL) radars, and the government shut down the EMI project. The state-owned Telecommunications Research Establishment became the sole authority on radar design, private companies were relegated to subordinate, secondary roles. According to Russell Burns, "the government's failure to enlist the support of EMI's brilliant research and development staff at a sufficiently early stage in the advancement of radar was a monumental policy blunder."

In April 1940 the TRE contracted EMI for modifications of the AI Mk. III airborne radar. In one month Blumlein and White managed to decrease the minimum operating range from $330 m$ ($1,000 ft$) to $140 m$ ($450 ft$). The redesigned radar, codenamed AI Mk. IV, was issued to the airforce in September 1940 and was actively used against the Germans in the final stages of The Blitz. The Mk. IV was followed by an intermediate version, the Mk. V that used manually operated strobe-following circuit for suppressing unwanted echoes. The invention is credited independently to Blumlein and Robert Hanbury Brown, but Blumlein's design was the first to be deployed. The pilot now had his own radar display, but the Mk. V still needed a skilled operator and thus could not be fitted to single-seat interceptors.

In October 1940 Blumlein was appointed lead designer of the AI Mk. VI radar for single-seat aircraft. In two months, the prototype ready for flight tests. By April 1941 Blumlein resolved the teething troubles, and in August 1941 EMI delivered the first production Mk. VI's to the airforce. Blumlein's auto-strobing principle, implemented for the first time in the Mk. VI, was later used in British ASV and H2S aircraft radars, the Rebecca and Oboe navigation systems, and in early American radars. The Blumlein transmission line, patented in October 1941 and intended for supplying short power pulses to the magnetrons, was first used in the GL Mk. III anti-aircraft radar and the Type 261, 274 and 275 anti-submarine radars that were deployed after Blumlein's death.

In January 1942 the Minister of Aircraft Production instructed the EMI to begin development of the H2S airborne ground scanning radar. The crucial question of which transmitting tube, the cavity magnetron or the klystron should be used, remained unsolved. The magnetrons had higher energy output and thus longer range, and were easier to manufacture. However, they were also virtually indestructible, which why the authorities were reluctant to issue them to air units operating over enemy territory. Thus the EMI and TRE designers had to develop two competing prototypes, using klystrons and magnetrons, respectively. The magnetron-based H2S was tested first on 17 April 1942; it worked but range was limited to a few miles. The klystron-based H2S, developed by the Blumlein team, was tested on June 2. It had poor range, too, and suffered from gaps in its polar diagram. Meanwhile, the TRE engineers reported significant improvements in the performance of their radar. When Blumlein learnt about the progress made at TRE, he made a decision to board the next test flight to see the results himself, just like he did during the AI Mk. VI tests in 1941.

Death
On 5 June 1942 Blumlein filed a patent application for his Miller integrator, and departed from London to the TRE base at Malvern College, in the company of engineers Frank Blythen and Cecil Brown. Flying tests of the H2S prototype designed at the TRE began on June 7. At 14:30 the converted Handley Page Halifax bomber took off from RAF Defford, carrying five crew members, three TRE engineers, Blumlein, Blythen and Brown. An hour and half later one of four engines failed, starting a fatal fire. Flames quickly engulfed the wing, the airplane broke apart in the air and crashed in Wye Valley near Welsh Bicknor. There were no survivors. On the next day Shoenberg, who was summoned to the crash site to identify the dead, personally visited Blumlein's widow to tell her of the her husband's death. On June 13 the remains of all victims were cremated at the Golders Green Crematorium.

The accident enraged Winston Churchill, who ordered a thorough investigation. The cause of the crash was eventually traced to negligence of one of the mechanics who serviced the engines of the Halifax. Circumstances of Blumlein's death, but not the very fact of it, were immediately classified. Blumlein's obituary published in Daily Telegraph on 10 June 1942 stated that he died "on active service"; obituaries of Blythen and Brown, published on 11 June, reported "result of an accident". It is likely that the accidental manner of Blumlein's death was censored out of the obituary at the request of EMI management, rather than military authorities. Nevertheless, a least one London newspaper made a connection between Blumlein's death and alleged "hush-hush work" at EMI, thus exposing the company and its employees to German attacks.

Intellect
Blumlein, a modest person in everyday life, was well aware of his extraordinary mental abilities. Philip Vanderlyn recalled that "Blumlein had one fear - that his inventive streak would fail him", and that Vanderlyn himself could not grasp that irrational fear ("if you have this gift, you always have it"). Phenomenal state of his intellect manifested itself for the first time during his college years, although some signs of it were probably evident in early childhood. Blumlein possessed exceptionally good memory; he could process new knowledge faster than any of his peers, and he retained new knowledge without apparent effort or difficulty. Fellow students thought that Blumlein "did not work", while in reality he did, although much more faster and effectively. They did note, however, his enduring patience, his ability to listen to others, and his physical ability to work long hours effectively. In peacetime, Blumlein often spent weekends in the laboratory; in the opening months of the Battle of Britain he usually worked until 10 p.m., and then proceeded to his volunteer air defence or firefighting station for the rest of the night.

Blumlein's quest for perfection and the speed of his thought often caused misunderstanding and conflicts. He was able to easily solve the problems that puzzled his colleagues for years, and he fixed mistakes made by others. This could alienate people, especially after experience had proven that the "upshot" Blumlein was right, and they were wrong. Sometimes fast pace of his mind would show itself in unusual and frightening ways. Blumlein, an amateur aviator and motorcyclist, was an aggressive but skilled and lucky sports car driver. Colleagues recalled that he would often "draw" schemes and formulas on the wind screen of his car while driving, especially at night. He continued his mental work even during risky maneuvers. His passengers, already scared by high-speed drifting on slippery streets, were utterly horrified, yet Blumlein always managed to get home safe.

Blumlein was able to lead several research and development projects concurrently, and had the ability to switch between two projects in an instant. More than once he had to leave imcomplete work to his colleagues and move on to a different field, often completely unrelated to his past experience. This experience was not lost, and Blumlein often returned to apparently abandoned topics. In 1932, four years after leaving the field of telephony, Blumlein "unexpectedly" patented a new type of loading coil for long-distance lines; it is likely that he arrived at the idea while developing his electromagnetic record cutter head. Alan Hodgkin, who worked with Blumlein during the war, said in 1977 that "Blumlein's versatility makes it difficult to do justice to his genius. Today he was what might be called a systems engineer, that is a person who looks at the engineering and cost effectiveness of some development as a whole... In the 20s and 30s such people were rare and Blumlein was very much a pioneer - indeed one might refer to him as the first systems engineer ... a truly multi-disciplinary engineer of the kind badly needed in an age of specialisation".

Mentor and students
Blumlein did not receive formal training in electronics, which did not exist yet as an academic subject during his college years. His education at City and Guilds was limited to electrical engineering. He learnt the basics of emerging electronics during his brief work with professor Mallett and at Western Electric. He did not have a formal academic advisor, until being "adopted" in March 1929 by Isaac Shoenberg. Shoenberg would become Blumlein's mentor, patron and immediate senior in the corporate structure for the rest of Blumlein's life. At the height of the Great Depression Shoenberg selected and hired a small but effective group of talented engineers and physicists which had no precedents in British history. He recognized Blumlein's capacity and continuously supported him with the company's resources, which were key to Blumlein's success as an inventor. Shoenberg regularly and closely controlled the progress of each research group, thus relieving Blumlein of mundane managerial work.

However, the same Shoenberg prevented Blumlein from becoming a scientist. He exploited Blumlein as an inventor and engineer, and enforced EMI's policy on keeping all research secret. Blumlein did not object; he was completely immersed into day-to-day engineering and applied research and did not seek publicity. In seventeen years of professional work, he published only one journal article and appeared once at a trade conference. James Dwyer McGee recalled that "It is not stretching credibility to compare Blumleing to Rutherford. I came from working under Rutherford to working under Blumlein, and so I was able to compare the two men in close quarters <...> Dennis Gabor suggested that Rutherford might, mutatis mutandis, have been a great inventor, that is, like Blumlein. It is my opinion that Blumlein, given the right circumstances, could have been a Rutherford".

Blumlein's own teaching teaching talent was first noted during his assistantship at City and Guilds. Eric Nind recalled that 22-year-old Blumlein "was very good at explaining anything... plenty of inexhaustible patience", that he was good in presenting even the complex mathematics in a clear and concise manner, and that he posssessed the skill of formulating and asking leading questions that "would absolutely be the 'nub' of the question that was puzzling [the student]". Nind and another Blumlein's student of the period Eric White would later become key engineers at the EMI laboratory and inventors in their own right. Blumlein was very good at converting new people to his ideas; his approach to electronic design and his reference solutions easily spread within the British engineering community. For example, logic gates of the Automatic Computing Engine, clearly traced to Blumlein's long-tailed current switch, were designed by Ed Newman and David Clayden, who joined the EMI laboratory staff in 1939 and 1941, respectively. Colleagues and students unanimously recall Blumlein's modesty and integrity in matters of intellectual property. He scrupulously recorded personal inputs of each associate, and always paid his due when the ideas were worth patenting. In 46 of his 128 patents, Blumlein shared his rights with his subordinates. McGee, one of these co-authors, wrote that "tremendous integrity ... was the most outstanding characteristic of Blumlein that I can remember ... the the kind of person who I don't think would ever cheat anybody else of the smallest thing". Hodgkin concurred, saying that "not only did this make working with Blumlein a lot of fun, it also created the climate in which new ideas are generated".

Design process
Blumlein's work philosophy relied on the top-down "good design" process, from basic theory to production samples. According to biographer Russell Burns, it had much in common with his great predecessors and contemporaries like Brunel, Steinmets and Tesla. Their inventions, wherever possible, were backed by scientific analysis and careful design process. Unlike self-taught experimenters like Edison, they relied on fundamental science; there was no place for countless but fruitless experiments that were the essence of Edison's method. Their inventions, unlike the compilations of prior knowledge by Marconi or Baird, were highly original and novel. Blumlein or Brunel boldly advanced new concepts; they not constrained by tunnel vision that plagued Marconi and Baird.

Blumlein rejected Edison's trial and error approach. He insisted that the designs must be designable: the properties of a prototype should agree with theoretical estimates, the properties of any production sample should not fall below the finalised specifications. Blumlein followed the practice himself, and promoted and enforced it in the laboratory. The main feature of a good design, according to this approach, is a good match between estimates and real measurements. Any mismatch is at the very least a concern requiring further investigation. When measurements matched estimates from the start, Blumlein's was firmly confident that the design was good. His instinctive trust to good designs extended beyond the workplace. Blumlein had only a cursory understanding of aerodynamics but he was confident in good design of his de Havilland Moth airplane, and often tested its limits in flight.

Blumlein usually began his design cycle with top-down theoretical engineering analysis. After preparing a test prototype, he would compile a detailed test program, down to a clean spreadsheet for recording the measurements. Electronic measurements in the 1920s were a non-trivial and time-consuming task. There were no computers, no spectrum analyzers, even no analogue oscilloscopes. "A look inside" a recorded soundwave required making a microphotograph of the mechanical or optical soundtrack and performing a Fourier transform with a pencil and a slide rule. Old school engineers preferred to tune their designs by trial error, relying on their own senses and intuition; Blumlein tried to discourage this practice whenever possible. He admitted that he did not have hands-on experience of the older generation, but was confident that a thorough theoretical analysis more than made up the difference.

In the 1920s, Blumlein's favourite building blocks were signal transformers and closely coupled inductors in general. In a coupled inductor, inductance of each winding is determined primarily by common mutual inductance. Coupled windings can be easily matched to a very high accuracy (1 ppm or less), and this precision is easily and consistently reproduced in mass production. Coupled-inductor bridge circuits were used in at least nine of Blumlein's patents, including the "Low level altimeter based on earth capacitance" that was the subject of debate in 1977. Blumlein learnt the art of designing with valves gradually. In the 1920s valves were used almost exclusively to generate and amplify harmonic signals, usually in a narrow frequency band. The use of valves for shaping wideband pulse signals, which is essential to analogue television, did not exist yet. By the middle of the 1930s Blumlein mastered this technology and developed his own circuit design style based on a small set of building blocks: constant-impedance RC-LC networks, delay lines, negative feedback loops, cathode followers and cathode-coupled circuits in general.

A well-engineered product, according to Blumlein, should not need fine-tuning on the production line, nor periodic alignment in regular use. This explains his defined current principle: operating current of each valve must be limited by design, so that the inevitable initial mismatches, long-term drift or ageing would not adversely affect operation. To this purpose Blumlein widely used current-limiting components: resistors, chokes, active current sources) and negative feedback. Two of his seminal inventions, the long-tailed current switch and the cathode follower, were direct applications of this principle.

Private life
Blumlein's political views are unknown. It is known that during the 1926 general strike he and three of his associates voluntarily replaced absent technicians at the Euston station telephone exchange. The four strikebreakers worked twelve-hours shifts, helping to keep the remaining railway operations alive, and were generously rewarded by the railway and the ISEC.

In 1930 Blumlein met Doreen Lane, a private school teacher. Blumlein and Doreen married in April 1933. Their first-born son died in infancy; their second and third sons Simon John Lane (born 1936) and David Antony Paul (born 1938) survived and outlasted their father. By 1933 Blumlein was promoted to third-in-command in the EMI engineering hierarchy, but actually was second-in-command reporting to Shoenberg directly. He was very well paid, and able to provide comfortable lifestyle to his wife and sons. Doreen took over and managed all homemaking needs; very soon Blumlein became completely dependent on her in everyday life. Despite his work and family responsibilities, he remained an avid and aggressive driver and aviator. According to Doreen, he was well aware of the risk of accidental death, saying once that "I shall be gone like a candle blown out .. but you will have to go on living". Blumlein "believed his afterlife lay in whatever good or bad he had done in the world — and in his children".

Casual observers saw the Blumleins as a model happy family, however, according to Doreen this was quite far from truth. Blumlein, she said, was a 'very difficult', and 'very temperamental' person, prone to outbursts of rage over petty issues. Shoenberg was concerned about Blumlein's bad temper, and believed that Doreen had a beneficial effect on his impetuous personality. In his own ways, Shoenberg took care of the Blumleins; he often visited their home and mediated family conflicts.

Arguments over priority


Blumlein's contribution is spread over 128 public patents and a multitude of internal corporate reports and memos. Some of the patents, in particular the United Kingdom patent 394325 "Improvements in and relating to Sound-transmission, Sound-recording and Sound-reproducing Systems" are, in fact, fundamental works of applied science. The peak of Blumlein's productivity as an inventor occured in 19341937, during his work on television.

British writers like Barry Fox or Marcus Scroggie called Blumlein the inventor of the cathode follower, the long-tailed pair and the negative-feedback amplifier. These statements are debatable, because the same ideas were developed concurrently by other people and organizations in different countries. Often, the issue of absolute priority has no definite answer. Blumlein is universally credited as the sole inventor of the Blumlein delay line and the ultralinear valve stage; these works had no analogies in prior art. Blumlein's long-tailed pair, on the contrary, was merely one of many consecutive intermediate implementations of the same, already known idea. Its evolution continued after Blumlein's death; the final configuration was developed by other inventors.

Negative feedback amplifiers
The North American version of the history of electronics asserts that in August 1927 Harold Stephen Black, a twenty-nine-year old systems engineer at Bell Labs, had an epiphany. Black was looking for ways to decrease distortion of valve repeaters on transcontinental telephone lines, and suddenly realized that the problem can be solved by enclosing the amplifier inside a negative feedback loop, if it is possible to prevent the amplifier from oscillating. Black has proven his idea experimentally, however, neither the Bell Labs management, nor the Patent Office saw its potential. Black was allowed to publish it only in 1934 and received a patent in 1937. According to the same legend, the theory of negative-feedbacks amplifier was developed in 19271940 by Black, Hendrik Wade Bode and Harry Nyquist. In real life, however, Black did not possess the necessary mathematical skills; mathematicians like Thornton Carle Fry considered Black's analysis "beyond contempt". The fundamental stability criterion was formulated independently by Felix Strecker in 1930 and by Nyquist in 1932. Later in the 1930s Bode extended Nyquist's criterion for amplifiers to electrical networks in general; critical contribution was also made by Bernard Tellegen and Frederick Terman.

The legend omits the fact that in 1928, when Black's invention remained a corporate secret, Philips patented their own design of a negative-feedback audio power amplifier. When Blumlein developed his version of negative-feedback amplifier in 1932, one of the objectives of the design was to circumvent the claims of the Philips patent. To do so, Blumlein and Clark replaced voltage feedback described in the patent with current feedback. In an internal memo dated 19 July 1932 they outlined various benefits of feedback, however, in their public patent application (1933) they mentioned only the decrease in output impedance. The Blumlein-Clark amplifier did not make it to the production line; Blumlein's work on negative feedback theory was never published. However, it became one of Blumlein's favourite design tools, and was empoyed in his key inventions like the cathode follower, the long-tailed pair and the Miller integrator.

Cathode follower
The very first cathode follower was patented in 1925 in the United States by Anthony Winther. Winther designed a novel radio receiver circuit that used vacuum tubes to convert voltage to current, and interstage transformers to convert current to higher voltage. For years, Winter's invention did not see much use, and no theory of its operation existed.

Blumlein used the cathode follower for the first time in his 1932 audio power amplifier. A theoretical analysis of operation was included in an internal memo signed by Blumlein and Clarke on July 19, 1932. It formed the core of the 1934 British patent 448421, which was credited solely to Blumlein and which belongs to a narrow circle of his principal, fundamental works. The main benefit offered by the invention to the industry was the ability to suppress undesirable effects of parasitic capacitances and thus extend the bandwidth of valve amplifiers. The term cathode follower appeared for the first time in a 1936 patent application by Blumlein (a pentode-based follower) and a 1937 application by Eric White (the White follower).

The EMI team led by Blumlein widely used followers in measurement instruments and in television broadcasting equipment. Acording to a 1938 article by Cecil Brown, the four main areas of application were high input impedance video amplifiers, low output impedance driver circuits, drivers of capacitive loads, and linear voltage regulators.

Long-tailed pair
The need for the balanced stage, or long-tailed pair, emerged around 1930 in conjunction with the developments in electrocardiography (ECG) and electroencephalography (EEG). The ECG and EEG instruments had to amplify very faint signals in presence of substantial ambient noise and hum, so they had to have a balanced (differential) input stage. They had to operate down to very low frequencies and retain the shape of input signals, so they could not use isolation transformers to convert balanced input to single-ended signal. The earliest biological amplifiers employing symmetrical pairs of triodes appeared in 1934.

In 1936 Blumlein patented his version of a differential amplifier, intended for processing wideband pulsed and video signals. Although he operated with fairly high frequencies, he faced the same problems as the designers of ECG and EEG instruments: bandwidth of commonly available isolation transformers was too narrow for the application. His circuit, as described in the patent, could not amplify DC signals, but it ensured superior common-mode rejection ratio (CMRR) due to different biasing arrangement. In 1937 Franklin Offner proposed a series of differential amplifiers, including one very similar to Blumlein's; Otto Schmidt published an alternative design built with pentodes. Finally, in 1938 Jan-Friedrich Tönnies published the now familiar circuit with bipolar power supplies. It had fairly high CMRR, and it could amplify DC signals. In 1941 Schmitt published a thorough analysis of operation. More improvements followed in postwar years; around 1950 the technology was mature. American authors hailed Schmitt and Offner as the fathers of the long-tailed pair; the British insisted on Blumlein's priority.

As Jack Copeland wrote, "we can only speculate as to what his [Blumlein's] approach to the design of digital computers would be", but Blumlein's implementation of the long-tailed pair became a common building block of early British computers. Cathode-coupled logic of the EDSAC computer was a direct development of Blumlein's current switch. The circuits had very good clipping behaviour and did not invert the signals, making inverters unnecessary.

Miller integrator
The Miller effect in electronic amplifiers with resistive loads has been known since 1919. The effect is caused by negative feedback via the parasitic capacitance between input and output terminals of a valve or transistor, and manifests itself in the early roll-off of frequency response, severely limiting bandwidth. In the middle of the 1930s Blumlein used the Miller effect on purpose, to create an active integrator. The first circuit employing the idea, a sawtooth wave generator for television, was patented in 1936. Blumlein would apply the concept to various circuits designed for television and radars, however, he did not file the application for the integrator per se until two days before his death. The patent 580527, having priority from 5 June 1942, was issued posthumously and assigned to Blumlein's widow. Owing to wartime secrecy, new patents were not published immediately. After the war, it was found that Blumlein's patent 580527 was predated by patent 575250, issued to Joseph Whiteley of A.C. Cossor, and having priority from 17 February 1942.

The term Miller integrator, meaning "using the Miller effect", was suggested by Blumlein himself, and is sometimes misconstrued as "invented by Miller". In 1946 Marcus Scroggie launched a campaign for renaming it to Blumlein integrator, that continued into the 1970s with little success. Nevertheless, books describing the Blumlein integrator were published in the United Kingdom until at least 1995.

Posthumous recognition
English-language, particularly British, literature on electronics retained many terms named after Blumlein: the Blumlein pulse-forming generator, the Blumlein pair of stereo microphones, the Blumlein 250 equalization for cutting coarsegroove records, and the Blumlein waveform of the 405-line television system. British and American historians of electronics continue to call Blumlein a genius. However, authors of popular literature refer to Blumlein merely as "the inventor of stereo". During his life, Blumlein was never well known to general public, neither at home, nor abroad; after death, he did not receive as much attention as his contemporaries Harvey Fletcher, Alan Turing or Vladimir Zworykin.

According to Barry Fox, "there is no simple explanation for Blumlein's lack of recognition. There is just an unfortunate but fascinating set of circumstances." The most obvious and relevant is the wartime secrecy that shrouded Blumlein's work for the military and the cause of his death. The Official Secrets Act prevented historical research for thirty years; when the limitation prescribed by law was lifted, many witnesses had already died, and many documents were lost or destroyed, including all TRE material on Blumlein. There probably weren't many such documents from the start: the TRE was notoriously known for poor recordkeeping. The EMI, on the contrary, carefully preserved its internal records. However, following strict confidentiality rules imposed by Shoenberg, the company kept its archives locked. No researcher was allowed inside, and no explanation given. Although by 1983 the EMI still possessed a large collection of old equipment, Blumlein's historical stereo recording set was destroyed during a cost-cutting campaign.

After the war, the former TRE researchers Taffy Bowen, Bernard Lovell, Albert Rowe and Robert Watson-Watt became successful academics, executives and prolific writers. Their statements, quite naturally, described their own experience at the TRE, but not the role of its private contractors and consultants. Systemic bias was already evident in September 1945, when Air chief marshal Philip Joubert de la Ferté publicly protested against overstating achievements of the TRE and downplaying the role of Blumlein and Clifford Paterson. Later, in the 1957 book Three Steps to Victory, Watson-Watt credited Blumlein as "the key man in H2S", but in immediate postwar years the public was not aware of his contribution.

In 1976 Barry Fox, Francis Thomson and EMI petitioned the Greater London Council to commemorate Blumlein with a blue plaque at his former home in Ealing. It was installed in June 1977; Alan Hodgkin, the person chosen to unveil the plaque, delivered a speech that sparked a public discussion about the 1942 crash. Popular journals published memoirs and biographical articles about Blumlein, but the circumstances of his death remained classified. In 1981 Barry Fox launched a campaign for immediate publication of Blumlein's stereo recordings that were still locked in the EMI vaults. At the very least, the perishable and combustible acetate film had to be transferred to a safe medium. One year later the company finally agreed to release the reels to independent restorers; they were transferred to nitrate film in 1982-1983, but not shown to the public until 1992.

Two lengthy, but by far incomplete biographies of Blumlein were released almost simultaneously, by Robert Alexander in 1999 and by Russel Burns in 2000. Blumlein's first biographer, Basil Benzimra, began collecting material in 1967 but soon abandoned work due to poor health. In 1972 the project was taken over by Francis Paul Thomson, a former commando and author of diverse non-fiction books.. British Institution of Electrical Engineers (IET), and later the Royal Society endorsed Thomson as the official biographer; the other researcher, Russel Burns, voluntarily stepped aside. Thomson often spoke about Blumlein and boasted about his private archive of Blumlein-related material, but failed to deliver his much-advertised book. In 1992 the IET relieved Thomson of his responsibilies and demanded to release his Blumlein papers to the public. This did not happen either; Thomson literally disapperared. He died in 1998 and his archive, if it ever existed, was lost. Burns and Alexander resumed their research, but by this time key witnesses were already dead. The biographers had to rely primarily on archive evidence. Barry Fox criticised Alexander's book, in particular, for excesses in technical analysis of the patents to the detriment of flow and logic.

In February 2017 The Recording Academy awarded Blumlein the Technical Grammy for his inventions in stereophonic sound. In response to the announcement Sir Lucian Grainge, chief executive of the Universal Music Group (owner of the former EMI assets) said that the company was "currently developing" a a film about Blumlein’s life and work.

Alan Blumlein Way is a road on the Tektronix campus in Beaverton, Oregon, in keeping with their policy of naming roads after those who made significant contributions to the knowledge and understanding in the field of electronics. There continues to be a meeting room named the Blumlein Room in the IET headquarters at Savoy Place, following a major refurbishment in 2015.