International projectionist (Jan-Dec 1957)

VARIABLE-DENSITY [Continued from page 11) which shows that while his remarks are true in reference to Western Electric type light valves of the 1928 period, they certainly do not apply to the more modern type of light valve modulators used in the Western Electric (Westrex) sound recording systems4. The introduction of the so-called Wente cyclindrical lens close to the film plane in present-day variabledensity modulators makes the recording essentially variable intensity rather than variable time. This is due to the fact that the image height never exceeds the circle of confusion of the modulator optical system. Coincident with improvement in optics, there has been a vast improvement in light valve design. With Alnico V permanent magnets, the new sealed light valve has an insignificant resonance peak, and is linear over approximately a 60 db range. Variable-Density Awards Apart from these technical considerations, critics of variable-density recording will have a difficult time explaining away the fact that during the period extending from 1930 to 1946, the Academy sound awards were given to only three pictures recorded with variable-area, the rest going to Western Electric recorded pictures. Since that date the issue has become confused by the introduction of variablearea by Westrex, and also by the use of magnetic tracks for both original and theatre reproduction. Surely the overall evaluation by the industry over a period of many years cannot be ignored. Anybody defending the virtues of variable-density recording must face the fact that there has been a noted swing to variable-area in recent years. In my opinion this swing has little, if anything, to do with the relative merits of the two recording systems, but can be traced to technical innovations which are favorable to the use of variable-area. For example, the use of negative-positive color films has resulted in an increase in the use of variable-area since it was felt that the variable-area would be somewhat easier to handle. This opinion, however, is not held by all experts in the field, and the movement to variable-area might conceivably be reversed at any time. The proposed use of magoptical recording has favored variable-area largely because the reduction of variable-density track to one-half its width would be undesirable in many theatres with insufficient amplifier gain. The growing popularity of direct-positive recording in intra-studio operations also favors the use of variable-area. In summary, it may be said that both variable-area and variable-density are capable of giving excellent sound quality. There have been vast improvements in recent years in both systems, and in the sound emulsions available for these recordings. Both systems require precise laboratory control, and in the opinion of this writer, anybody suggesting either one is immune to such control is doing a disservice to the motion picture industry. 1. "Elements of Sound Recording," Frayne rnd Wolfe, p. 350 et seq., John Wiley & Sons, Inc., 1949. 2. "Elements of Sound Recordinq," Frayne and Wolfe, p. 386, John Wiley & Sons, Inc., 1949. 3. "Modulated High-Frequency Recording as a Means of Determining Conditions for Optimal Processing," J. V. Baker and D. H. Robinson, Journal SMPE, vol. 30, p. 3, January 1938. 4. "An Improved 200-mil Push-Pull Light Valve Modulator," J. G. Frayne, T. B. Cunningham, and V. Pagliarulo, Journal SMPE, vol. 47, p. 494, December 1946. VARIABLE-AREA (Continued from page 11) when the scanning slit departs from correct azimuth. Spurious harmonics are thus generated; but azimuthal errors so gross as to make these harmonics audible as distorted sound simply do not occur in the field. Speaking from practical experience, the writer has never once encountered azimuthal maladjustment of the soundhead optical tube in any theatre. My reference to the ease of noiseproofing v-a tracks was concerned mainly with the ease of visually checking the effectiveness of v-a biasing. Visual inspection of v-d tracks yields less definite information. Modulate-Beam Restrictions It is true that conscientious lab engineers daily strive for optimal densitometric control with both types of soundtrack, and in negative and positive records. But the fact remains, Doctor Frayne's statement to the contrary, that the densitometric requirements of v-d tracks are relatively critical. If this were not true, so many studios would not have switched to v-a tracks for multilayer color prints. "The density of variable-area tracks may vary over considerable limits with remarkably small sound-output variations. This, of course, permits considerable latitude in laboratory work without sacrifice of quality or volume output." (Balph H. Townsend, RCA.) It is only necessary to avoid a track density so great that the finer striations of the high-frequency waveforms are attenuated in reproduction by fog. Such great exposure and processing latitude is not allowable in any system of v-d track production, for the modulated-beam method does not tolerate use of the low-exposure '"toe" nor the high-exposure "shoulder" of the emulsion scale, and the glow-tube method employs only the toe, and fails in the straight-line portion of the exposure curve. From the standpoint of actual practice, we encounter much larger variations in v-a track densities every day than are permissible in v-d tracks. These do not appear to affect reproduction in any way. We even find obvious errors in v-a tracks which, however, produce no detrimental effects in the sound. The existence of such errors as incorrect lateral adjustment of biasing valves reveals that perfection in commercial practice is the exception, not the rule. V-a tracks are remarkably tolerant of many kinds of errors and, furthermore, make such errors readily visible. Variable-density recorders of truly variable-intensity characteristics were referred to by the writer as instruments of the "modulated-beam" type. The practical functioning of improved Western Electric recorders as devices of this class is assuredly acknowledged, as is also the well-known excellence of Westrex sound-recording apparatus. No deprecation of Westrex sound equipment was intended. Need for Careful Control While the writer is admittedly less than overawed by Academy awards in any department of movie production, the recognized need for careful control in recording and film processing when the v-d method is used may well be a contributing factor to the general excellence of commercial v-d feature-film tracks. Simpler methods invite carelessness. But on the other hand, and in spite of back-slapping in Hollywood mutual-admiration societies, the sound quality of v-d tracks 32 INTERNATIONAL PROJECTIONIST • SEPTEMBER 1957