Projection engineering (Sept 1929-Nov 1930)

Projection Engineering, May, 1930 Page 15 facturing concerns, but many problems, such as camera-silencing, set construction, correction of acoustic defects by re-recording, etc., require work in the field. Sensitometry, and the control of photographic elements in the developing and printing of sound tracks on film, are of obvious concern to the sound engineer, since the most carefully exposed sound negative may be ruined by poor processing in the laboratory, and, conversely, lack of correlation between the photochemical elements and exposure conditions may result in degradation of quality or even loss of takes. One or more photographic specialists are therefore found on the staff of every adequately organized sound department, and a routine of test strip preparation to indicate optimum conditions of development is carefully maintained. Centralized Installation As shown in Fig. 2, recording organization is in general somewhat more elaborate where a central power, amplifier, and recording installation is used instead of portable units. The centralized scheme usually results in increased specialization. The Chief Mixer, corresponding to the Recording Supervisor of Fig. 1, does not have jurisdiction over the final step of engraving on wax or exposing film. These functions, instead, constitute part of the responsibility of a Chief Transmission Engineer, who is concerned with the operation of the plant, exclusive only of the stage, and its maintenance throughout. Alternatively, the mixers may also be under the control of the chief transmission engineer, who then becomes an assistant to the recording director in the immediate vertical line below the latter. With the addition of disc recording, also, various supplementary functions enter the organization picture, e. g., wax shaving, laboratory processing of discs, etc. The latter, added in Fig. 2 as merely a single line, is of paramount importance in those companies which release principally on disc and have their own pressing plants. These would really require another organization chart for complete treatment, which need not be included, however, in a general paper. Too Many Applicants Before closing the subject, I should like to invite attention to an economic phase of the sound problem which is of foremost interest to many people outside of the industry. Any sound executive's mail reflects a great aspiration on the part of many radio and electrical technicians to get into the movies. This desire arises partly from the glamour of the business, partly from the publicity with which it is so richly endowed, and partly from the relatively high salaries which successful sound men command. Furthermore, there was an acute scarcity of sound men in Hollywood during the transition from silent to sound pictures, and the news of this El Dorado is still reverberating among the ambitious and the dissatisfied— unfortunately with a time lag of 1 to 2 years. As is usual in such cases, the supply has more than caught up with the demand, even during peaks of production. During periods of only moderate activity, as at the present writing (March, 1930), there are considerable numbers of qualified sound engineers out of work in the Hollywood district. The number of jobs is at best very limited. Variety, in its survey of motion-picture studio employment, reported in its issue of January 8, 1930, gave the following figures for sound personnel in the Western Studios : Warners, 193 ; Metro Goldwyn Mayer, 147; Paramount, 105; Universal, 100; Fox, 75; United Artists, 44; Metropolitan, 41; RKO 32; Pathe, 32; First National, 29 ; Columbia, 22 ; Tiffany, 15; Tec-Art, 12; Hal Roach, 10 ; James Cruze, 9 ; Mack Sennett, 4 ; Educational, 4 ; Larry Darmour, 4 ; Miscellaneous, 71 ; Total, 949. While in some cases these figures have been increased since the tabulation, it is clear that there are only about 1000 sound jobs in Hollywood. This is surely nothing to write home about, especially as Los Angeles affords relatively few jobs in allied fields to the man waiting for a moving picture sound connection. It may be conceded that many of the men who are now knocking at the gates are just as good as those who are inside, but the ins are in, and the mortality among them is not sufficiently high to justify extravagant hopes on the part of the waiters in ante-rooms. Furthermore, the introduction of student engineering courses in some of the studios, the association of some of the producers with the electrical manufacturing companies, and the prior rights of eligible men in other departments of moving picture companies, further decrease the opportunities for immediate entrance for men whose experience has been confined to other fields. In short, sound must echo the warnings issued from time to time in the older branches of the industry against blind ventures in the direction of Hollywood, where neither the climate nor the scenery nor the presence of the national heroes and heroines can compensate for the lack of a personal income. A THE DECIBEL By John Dunsheath YEARS ago, in telephone work, the comparison standard of transmission was a "standardized" mile-long cable conductor. The 800 cycle mile of standard cable conductor was of such size that the "miles" was given by 10 .56 logio P1/P2, where P, and P2 were two powers involved. Later, the term TU was adopted to replace "standard mile," TU being the abbreviation of Transmission Unit. The desirability of having a uni versal standard prompted American telephone interests to discuss the proposal with various foreign telephone administrations with the idea of the general adoption of TU. There followed discussion as to the relative merits of a transmission unit based on common logarithms such as the TU, and one based on natural logarithms, such as the P 1 unit. Action, in 1928, took the form of a recommendation by the International Advisory Committee on long distance telephony of Europe that both units be recognized as standard. In either case is measured the logarithm of the ratio of two powers, currents or other quantities which express the magnitudes of the waves being compared. This insures that two sounds of the same general nature and quality differing by a stated number of units have the same difference in loudness regardless of their absolute loudness. The difference in loudness of two sounds may be measured by the number of intermediate steps or differences that can be identified in passing froin a sound of a given loudness to that of another. In view of the fact that the logarithm of. the intensity ratio td any base will in any case be proportional to the difference in loudness, a logarithmic unit is a suitable unit of relative loudness. The Advisory Committee advised that for |8 1, which is so defined that the number of units is given directly by the natural logarithm of a current ratio, the term Neper be adopted. In the case of TU the common logarithm of a power ratio is multiplied by ten to get the number of units. TU being in the nature of a derived unit the primary unit should bear the same relation to the common logarithm that the Neper does to the natural logarithm. The name "bel" was given the primary unit and since the number of TU corresponding to a given ratio is ten times the number of bels, the TU is equal to one-tenth bel. Thus is derived "decibel." While a unit of loss or gain may deal only with power ratios, means are at hand to use it to express ratios of current or voltage. Power ratios may be converted to dbs. by noting the logarithm of the ratios and multiplying that by ten. When the impedances are equal, current or voltage ratios may be converted to dbs. by noting the logarithm, multiplying it by 20. When impedances are unequal : Ndb=20'"sE7vl or where current ratios are involved : Ndb = 20lo (IQ» Ri (I2)2 R2 : 20lo, I2VR2 The word "Neper" is the spelling of "Napier" preferred by the originator of the idea of logarithms. The word "bel" is an abbreviated form of the name "Bell," after Alexander Graham Bell.