The Research and Development of 2 Channel Stereo

Talk: Tuesday 13 December 2011.The Research and Development of 2 Channel Stereo by Mr Jim Buckland – Member
The talk commenced with a brief review of the early developments in Hi-Fi sound reproduction and then followed an introduction to the development of 2 channel stereo. He started by reviewing the history of magnetic recording and the people involved. The inventor of stereo was a relatively unknown engineering genius named Alan Dower Blumlein who was an engineer with Columbia Records which became a subsidiary of EMI.. Blumlein held over 100 patents in the field of radio, TV and sound recording, including stereo records, stereo films, and surround sound. Blumlein was also involved in the development of radar but was unfortunately killed, with all on board, when a Halifax Bomber with a prototype of the H2S Radar System crashed in June 1942. (see
Jim then discussed the technicalities of “ 2 Channel Stereo”. Stereo sound systems can be divided into two forms:
The first is “true” or “natural” stereo in which a live sound is captured, with any natural reverberation or ambience present. The signal is then reproduced over loudspeakers to recreate, as closely as possible, the live sound. During “true” two-channel stereo recording, two microphones are placed in strategically chosen locations relative to the sound source, known as a Blumlein Stereo Pair which are on a 90 axis with both recording simultaneously. The two recorded channels will be similar, but each will have distinct time-of-arrival and sound-pressure-level information. During playback, the listener’s brain uses those subtle differences in timing and sound level to triangulate the positions of the recorded objects.
The second is artificial” or “pan-pot” (panoramic potentiometer) stereo, in which a single-channel (mono) sound is reproduced over multiple loudspeakers. By varying the relative amplitude of the signal sent to each speaker an artificial direction (relative to the listener) can be suggested. By combining multiple “pan-potted” mono signals together, a complete, yet entirely artificial, sound field can be created.
In the 21st century “true” stereo is mainly confined to recordings or broadcast of live, acoustic music, particularly classical music. Almost all pop records and movie soundtracks are of the “artificial” variety. Jim reviewed the development of stereo recording systems and the associated design of replay stereo amplifiers and loudspeakers and the features in many of them that debased the stereo image.. The work of Blumlein was resurrected in 1954 by EMI because the advent of magnetic tape provided a suitable medium for 2-channel recording. The work was started in 1954 and EMI was responsible for the recording aspects which took place in the Abbey Road Studios and Jim was responsible for the reproduction work. Initially there were considerable problems with the recording work and it was only the concept of the in line 2 channel head which made stereo possible. Jim was responsible for the research and development of the inline 2 channel head which made stereo finally work. Until that time the early work on recording had been done with spaced left and right heads which was of course highly subjective to linear displacement due to temperature changes and the precision of mounting position.
Stereo sound systems up to the late 50s was an expensive pastime. However, the advent of the 331/3 rpm vinyl record brought stereo sound to the general public. Jim played many extracts of early stereo recordings including the very first successful stereo recording which had been made in Studio 2 at Abbey Road under the direction of Sir Malcolm Sergeant. These included operatic vocal, piano and orchestra, taken from early magnetic tape. Some early stereo LP record extracts were demonstrated to show the quality that became available.
Listening conditions are extremely important and psychologists were involved in investigating the ideal stereo listening conditions. They concluded that this is best done in the dark or with your eyes closed. Alternatively a bunch of flowers placed between the speakers illuminated by a single spotlight with the room in darkness enhances the experience. Jim demonstrated this by projecting photographs of bunches of flowers of various types and colours, while he played his demonstration stereo recordings.
Jim concluded his talk by showing a video (with stereo audio) of Richard Hills playing Tiger Rag on the Wurlitzer Organ in the Assembly Hall, Worthing – mind-blowing!!! (see to demonstrate the facilities now available with modern technology. This was followed by a question and answer session.
Overall this was a fascinating journey through the history of stereo by someone who has a passion for the subject.
J Buckland/R Keir