Alan Dowler Blumlein - more than The Father of Stereo

It's my considered belief he was the greatest scientist engineer I have ever known. Had he lived he would have been the Michael Faraday of our age. Professor James McGee FRS

The genius Alan Dowler Blumlein was born in June 1903 in Hampstead, London to relatively wealthy middle-class family. His father was a German emigree and his mother was the daughter of a Scottish missionary. He was educated at Highgate School and the City and Guilds College, London; both times admitted on the basis of scholarships. After gaining his degree, his early work was related to the solution of problems with crosstalk on long telephone lines, and this he acheievd with a series of inventions of remarkable simplicity and brilliance.

In 1929, Blumlein moved jobs and joined the research department of the Columbia Gramophone Company where he started work on improving the primitive, electric recording apparatus of the day which consisted of a carbon microphone, primitive amplification and a moving-iorn disc cutter. Blumlein was involved in many of the developments which radically improved this system and set new standards for "hi-fi" performance in 1930. These consisted of:

As if this wasn't enough to be getting along with, Blumlein was spending a deal of time at around this date thinking about stereophony! His patent (No. 394,325) is still worth reading, and it's common to see his clear and brilliant ideas misunderstood and misrepresented even today. This patent was certainly 25 years ahead of its time, and his system, in which proposed the stereo microphone technique, panning technique, the +/-45 degree, stereo cutting method and acetate discs was only commercialised in the late nineteen-fifties; more than ten years after his death. The only application Blumlein saw of his stereo invention in his lifetime was an application to assist in the sound location of enemy aircraft in the Second World War.

In 1931 the Columbia and HMV companies merged to form a new electronics giant by the standards of the day and was christened Electric and Musical Industries Ltd. Soon after the merger, the new company started on television development in earnest. HMV had already demonstrated a 150-line mechanically scanned system before the merger. But the ambitions of the new company (and its director of Research, Isaac Schoenberg) far outstripped the standards of the day. So much so, that the concepts that were enshrined in the 405-line system remain the basis for all television systems and Blumlein had a hand in virtually every area of development including: the development of linear ramp genertors for the timebases; the extension of amplification bandwidths to several Megahertz; the establishment of DC clamping circuitry; the development of a.g.c. systems for television; stabilised HT circuits; and sync-pulse separators. Blumlein even contributed a considerable amount of the work towards the first electronic camera tube - the Emitron.

Most breathtaking of all, Blumlein was nearly entirely responsible for the specification of the 405-line television waveform. In almost everyway, this signal formed the basis for analogue television signals all around the world for forty years. When you watch television with stereo sound today, you are experiencing technologies in sound and vision which - to a very great degree - were invented by Blumlein. In fact, even if you watch TV with 5.1 sound, Blumlein is the architect, for his original stereo patent forsaw the use of surround sound with more loudspeakers!

Blumlein was responsible for the patents of several important electronic circuit configurations, for example, the long-tailed pair and the ultra-linear pentode circuit (although he didn't invent the rather silly term, "ultra-linear"). An important variation of this latter circuit appeared in an earlier patent (No. 425,553) published in September 1933, in which Blumlein and his co-author, H.A.M. Clark (of the Stereosonic paper), describe a circuit using "feedback" (they even use the word), to reduce the output impedance of pentodes. Incorrect then, that the concept of negative feedback should be attributed to H. S. Black who published his account four months later in January 1934!

Blumlein is also responsible for the "transversal filter" in which a signal is applied to delay-line with a series of taps along it; the signals from each tap - appropriately weighted - being added to derive the final output signal (Fig above). This was Blumlein's longest patent (No. 517,516) by far, and for a valid reason. This approach to filter design - an approach which conceives of a filter's response in terms of its time-domain "impulse-function", rather than in terms of frequency response - was entirely new; yet Blumlein understood comprehensively the advantage of such an approach which, indeed, forms the basis of all digital filters of today.

Blumlein was an inventor, not a self-publicist. Perhaps, because of this, and possibly because so much of his later work was shouded in wartime secrecy, so that his patents, weren't published during the war years, Blumlein, despite being known as the "Father of stereo", is still under-appreciated for his other contributions to the electronics of audio, television and RADAR. And this is especially unfair as Blumlein's last work in RADAR cost him his life.

He worked with the team who developed the H2S RADAR system. On 7th June 1942, he and two collegues took off from Defford in a Halifax bomber. Despite being a bright, clear summer's day - ideal for flying - on the return leg of the flight, the plane developed engine trouble and the pilot tried to land in a field. In so doing, there was a fire from which no one survived. The death of this man in 1942, during the darkest period of Britain's struggle against Germany, was important enough that Winston Churchill, Britain's war-time Prime Minister, was informed immediately of his death and news of the crash was suppressed to stop Hitler discovering about the setback to the RADAR project.

There is MUCH more about Alan Blumlein on these pages.


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