Abstract
A number of years ago a proposal was made by R. L. Miller of a way to reduce the band width of a speech channel by a factor of two, without an appreciable loss in quality. The proposal was to divide the speech band into three parts by filters at carrier frequency (0–1, 1–2, and 2–3.6 kc bands). Each of these bands usually contains one of the three principal vowel formants. The signal in each band is passed through a regenerative modulator, which halves the frequency of the formant and translates the neighboring frequency components downward correspondingly. The output of the regenerative modulators is filtered to a band width of one-half of the original. This throws out certain frequencies, but ordinarily they are of low amplitude and the loss is not serious. In this way the speech band is halved. At the receiving end the three component bands are separated and each band is frequency doubled and recombined. The recombined signal, having the original band width, is modulated back into the voice frequency range. Experimental verification of the essential principles involved has been made and the results are described.
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