Journal of the Society of Motion Picture Engineers ( Volume: 46, Issue: 1, January 1946)

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Intermodulation Distortion of low Frequencies in Sound Film Recording

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Publisher: SMPTE
Doc Type: Journal Article
Article Type: research-article
Abstract: Variable-density sound film recording is subject to intermodulation distortion in the low-frequency band which extends from the lower limit of the audible spectrum toward zero, but not to zero frequency. This distortion is the result of the “Bromide Drag” phenomenon and is in the nature of exorbitant gamma. Corrections may be made for gamma at any point in this exorbitant range, but only at the sacrifice of correct gamma for other frequencies. The popular intermodulation method of distortion analysis uses 60 cps as a low-frequency component, which frequency lies in the exorbitant band. The data obtained thereby are representative of the exorbitant conditions and are misleading if they are taken to represent the entire recorded frequency spectrum. The delta-db method of distortion analysis gives data representative of conditions in which the low-frequency component is zero frequency. The analysis shows, however, that the data are also representative of frequencies above the exorbitant band and, therefore, represent the general recorded frequency spectrum except for the exorbitant band. Optimum processing specifications should be based upon data representing both conditions—outside the exorbitant band, as indicated by the delta-db method (zero frequency), and inside the band, as indicated by the intermodulation method using several frequencies around 60 cps. Either method may be used alone for processing control data after all conditions have been determined and are known to remain constant. Practice has substantiated the merits of the principles expounded here.
Publication Date: 1946-01-01
DOI: 10.5594/J11861
Link: https://doi.org/10.5594/J11861
Author(s): Fred G. Albin

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Fred G. Albin; Intermodulation Distortion of low Frequencies in Sound Film Recording, Journal of the Society of Motion Picture Engineers ( Volume: 46, Issue: 1, January 1946); SMPTE, 1946. Available at https://doi.org/10.5594/J11861

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Fred G. Albin; Intermodulation Distortion of low Frequencies in Sound Film Recording, Journal of the Society of Motion Picture Engineers ( Volume: 46, Issue: 1, January 1946); SMPTE, 1946. Available at https://doi.org/10.5594/J11861

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<span class="citation">Fred G. Albin; <cite>Intermodulation Distortion of low Frequencies in Sound Film Recording</cite>, Journal of the Society of Motion Picture Engineers ( Volume: 46, Issue: 1, January 1946); SMPTE, 1946. Available at <a href="https://doi.org/10.5594/J11861" target="_blank" rel="noopener">https://doi.org/10.5594/J11861</a></span>

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<li>
Fred G. Albin; <cite id="bib-10-5594-j11861">Intermodulation Distortion of low Frequencies in Sound Film Recording</cite>, Journal of the Society of Motion Picture Engineers ( Volume: 46, Issue: 1, January 1946); SMPTE, 1946
<span class="doi">10.5594/J11861</span>
</li>