Distortion-Balance Tests for Motion-Picture Soundtracks

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Publisher: SMPTE
Doc Type: Journal Article
Article Type: research-article
Abstract: Regardless of how different two soundtrack negatives are in terms of product, process or treatment, they will contain the same amount of cross-modulation distortion if they both optimize at the same density on a given print when printed on the same printer. Sound-film technicians employ this principle intuitively when they purposely distort a negative to optimize a print. The following important points are made: (1) image spread distortion increases with amplitude and frequency and causes a shift in average level; (2) negative and print distortions are opposite in phase and tend to cancel algebraically; (3) distortion-balance tests using pulsed signals (which may be prerecorded on magnetic tape) provide a practical means of optimizing sound prints; (4) percent distortion (rather than decibels) is plotted against print density for a given negative or against negative density for a given print; (5) by examining the phase of the 400-Hz distortion component, one finds whether a print from a given negative needs more exposure or less to achieve net cancellation; (6) interpolation and extrapolation are easy because the curves of percent distortion vs density constitute a family of straight parallel lines over the practical range; and (7) optimum print density can be predicted from a knowledge of percent distortion in the negative—which means that this distortion rather than the negative density is the important factor. These tests may be evaluated with a meter, oscilloscope, densitometer or even a common loudspeaker.
Publication Date: 1977-09-01
DOI: 10.5594/J06761
Link: https://doi.org/10.5594/J06761
Author(s): Ralph R. Wells

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Ralph R. Wells; Distortion-Balance Tests for Motion-Picture Soundtracks, SMPTE Journal ( Volume: 86, Issue: 9, September 1977); SMPTE, 1977. Available at https://doi.org/10.5594/J06761

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Ralph R. Wells; Distortion-Balance Tests for Motion-Picture Soundtracks, SMPTE Journal ( Volume: 86, Issue: 9, September 1977); SMPTE, 1977. Available at https://doi.org/10.5594/J06761

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Ralph R. Wells; Distortion-Balance Tests for Motion-Picture Soundtracks, SMPTE Journal ( Volume: 86, Issue: 9, September 1977); SMPTE, 1977. Available at https://doi.org/10.5594/J06761

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<span class="citation">Ralph R. Wells; <cite>Distortion-Balance Tests for Motion-Picture Soundtracks</cite>, SMPTE Journal ( Volume: 86, Issue: 9, September 1977); SMPTE, 1977. Available at <a href="https://doi.org/10.5594/J06761" target="_blank" rel="noopener">https://doi.org/10.5594/J06761</a></span>

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Ralph R. Wells; Distortion-Balance Tests for Motion-Picture Soundtracks, SMPTE Journal ( Volume: 86, Issue: 9, September 1977); SMPTE, 1977
doi: 10.5594/J06761
url: https://doi.org/10.5594/J06761

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<li>
Ralph R. Wells; <cite id="bib-10-5594-j06761">Distortion-Balance Tests for Motion-Picture Soundtracks</cite>, SMPTE Journal ( Volume: 86, Issue: 9, September 1977); SMPTE, 1977
<span class="doi">10.5594/J06761</span>
</li>