Abstracts of Technical Articles by Bell System Authors 



StereopJwnic Reproduction from Film} Harvey Fletcher. On 

 April 9 and 10, 1940, demonstrations of the stereophonic reproduction 

 of music and speech, described in this article, were given at Carnegie 

 Hall, New York, N. Y. These demonstrations represented the latest 

 development in a series of researches by Bell Telephone Laboratories, 

 the first step of which was demonstrated in 1933 when a symphony- 

 concert, produced in Philadelphia, was transmitted over telephone 

 wires to Washington, and there reproduced stereophonically and with 

 enhancement before the National Academy of Sciences. 



For the present demonstrations, original recordings of orchestra, 

 choir, and drama were made at Philadelphia and Salt Lake City ; and at 

 a later audition the artist or director was able to vary the recorded vol- 

 ume and to change the tonal color of the music to suit his taste. At 

 will, he could soften it to the faintest pianissimo or amplify it to a 

 volume ten times that of any orchestra without altering its tone quality, 

 or he might augment or reduce the high or low pitches independently. 

 The music or drama so enhanced is then re-recorded on film, with the 

 result that upon reproduction, a musical interpretation is possible that 

 would be beyond the power of an original orchestra, speaker, or singer 

 to produce. 



Wave Shape of 30- and 60-Phase Rectifier Groups."^ O. K. Marti and 

 T. A. Taylor. The installation of mercury arc rectifiers with a total 

 capacity of 82,500 kilowatts by the Aluminum Company of America 

 at Alcoa, Tennessee and Massena, New York, was accompanied by 

 widespread increases in the inductive influence of the interconnected 

 power supply networks with resultant increases in the noise on exposed 

 telephone circuits. Because of the size of these installations, and the 

 complexity of the supply systems, it appeared impracticable to limit 

 the rectifier harmonics by the use of frequency-selective devices, which 

 have been successfully applied to certain smaller installations. How- 

 ever, the results of a cooperative study indicated that by means of a 

 relatively simple arrangement of phase shifting transformers, the equiv- 

 alent of 30- or 60-phase operation of the rectifier stations could be 

 secured. In this way, the important harmonic components on the 

 power systems were reduced to relatively small values, and wave shape 

 and noise conditions were restored practically to normal. 



> Jour. S. M. P. E., June 1940. 

 ^Elec. Engg., April 1940. 



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