Audio recording

Blumlein was soon looking for wider horizons and so he moved to the Columbia Gramophone Company in March 1929. According to Benzimra Blumlein told Isaac Schoenberg, the general manager, that he might not still want him when he heard the salary he was asking. Schoenberg’s reply was to offer him even more!

By that time the knowledge and skills slowly acquired by telephone engineers had been applied to make a new audio disc recording method which made mechanical systems obsolete. Any record company that stuck with the old techniques would soon be obsolete too. The patents for the new method were held by the Bell System (Western Electric) in America to which a royalty was paid for every record pressed. Blumlein was given the task of inventing an alternative electrical method which would not violate the American patents.

To do this he adopted the moving-coil principle which the Americans had not used. He and his colleagues are known to have been working on the design in October 1929 and a prototype was tested the following February. Electrical damping replaced mechanical damping to control the resonance of the cutting head and, with electrical filters, a wide frequency range was achieved with excellent linearity. A complete system was designed and built in-house, from new moving-coil microphones through the intermediate electronic circuitry to the final moving-coil recording head.

The first recordings were made in 1930 and they set a new standard for fidelity. Blumlein received a £200 bonus. But his thoughts had by now ranged beyond others' horizons to consider how a spatial impression of the artists' performance could be achieved using only two loudspeakers. He took out an incredible patent in 1931 with seventy claims relating to 'binaural' recording - in other words, stereophony. He was 25 years old at this time. When stereo records became a commercial reality in the 1950s EMI received nothing from this patent. Even after an extension, the patent had expired.

Blumlein's system was intended primarily for cinema use, but it also included records and was essentially that used for stereo records from the mid-1950s. The only widespread use that Blumlein lived to see was one of the few applications not covered by the patent. In World War Two a couple of thousand stereo sound locators were made for assisting in aircraft detection. With previous systems nearby gunfire could deafen the operators. Blumlein electronically limited the sound and used a cathode-ray tube (instead of earphones) for indicating the results.

Television

In 1931 Columbia merged with The Gra­mophone Company (HMV) to form Electric­al and Musical Industries Ltd, now Thorn-EMI. It was this new company that developed the 405-line electronic television system which became the standard British format and which remained in use until 1985. The format for the picture signal became a world standard, altered only to include colour and stereo sound. Blumlein was the principal architect of the waveform and some people call it the Blumlein signal.

The development of television at EMI was a team effort and involved names which have become legendary in British television: Isaac Shoenberg, J.D. McGee, E.L.C. White and others with of course Blumlein. Blumlein was a major contributor to the circuit design and he had a hand in other areas including the Emitron camera tube, transmission cables and aerials. Among the circuits he invented or developed were a novel sawtooth generator for scanning, negative feedback circuits and the cathode-follower. He also invented and named the long-tailed pair circuit which was devised to reduce interference at the receiving end of a new video cable laid to Alexandra Palace.

Radar

When the Second World War began engineers in Britain already had considerable experience of radar development, all of it conducted in secret. EMI had barely touched radar work but the television team had the expertise for dealing with pulse techniques. So it was that the team which developed television turned to radar. Blumlein, White and others were soon at work on 200MHz airborn-interception radar. This was followed by a model which searched for and locked on to an echo, thus allowing a fighter pilot to operate without a radar operator. The radar work involved a range of activities including frequency-shift keying, klystrons and magnetrons, anti-jamming circuits and so on.

It was during this radar work that Blumlein designed a ramp waveform or timebase generator more linear than any previously achieved. To do it he made use of a usually unwelcome effect in a triode valve circuit first noticed by John M. Miller and subsequently called the Miller effect. Blumlein called the circuit the Miller integrator, a name which stuck and kept his own name out of the electronics text books.

The next major work was a plan-position radar which gave a picture of the ground below the aircraft, so permitting very accurate navigation. It was code-named H₂S and was developed jointly by EMI and TRE (later the Royal Radar Establishment).

With two EMI colleagues and a good proportion of the TRE team, Blumlein was testing the equipment on board a Halifax bomber on 7 June, 1942 when an engine caught fire. The plane crashed, killing all on board. Despite this catastophe H₂S was completed and produced for Pathfinder and Coastal Command aircraft.

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