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Tinted Film and Sound Reproduction
The final and most crucial step in evaluating the effect of tinted films on optical sound reproduction is integration of the spectral curves of the tinted base materials with the S-4 photocell response which has alread\ been integrated with the radiant emission of the exciter i its shown in Fiji. 4 1 . This has been done in Figs. (>. 7. and 8.
Fi«z. 6 conclusive!) proves that yellow, orange, and red films cause no perceptible attenuation of sound
Visible Infrared
700 BOO 900 1000 1100 1200
Wavelength (m^)
Tunrfsten-excited S-.4 cell ' Bluisn pVeen film
Fig. 7 volume or other audio disturbance of anj kind. Fig. > reveals that the bluish green film all but eliminates the S-4 photocell's response to the visible spectrum, but whereas most of the response »>f this tvpe of cell occurs in the infrared, which is unaffected bv the bluish green dvc. the resulting sound-volume attenuation amounts to less than is noticeable, and even less than can he compensated for by a single Step on the fader. Reproduction is entirely satisfactory.
The bluish green sample plotted here has a sli^htlv greater photocell densitv than the deep blue plotted in
Visible
Infrared
400 50C 600 700 800 900 1000 1100 1200
Wavelength (nya)
Tungsten -excited S-<4 cell' Deep blue film
Fig. 8 Fig. 8. Most blue dyes, especially if thev incline to blueviolet in tone, transmit the low red rather freely, and the infrared perfectly. A few blue dyes are known which are opaque to low red and near infrared: but there is no reason to employ these relatively unusual colorants in tinted-film base.
W e mav safelv conclude, therefore, that all colors of tinted-base prints mav be intermixed with one another or with clear-base film without producing audible changes in sound volume when the optical soundtracks are reproduced bv photoelectric devices having a type S--1 response. Bluish green film of high color saturation presents the greatest photoelectric density, but not even with this color do soundtrack re-recording compensations or changes in projection-room fader setter appear to be necessarv .
(TO BE CONC LVDED)
International Projectionist December. 1963
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