Peakpicker: A Band‐Width Compression Device

A vocoder of the usual channel type has been used as the basis for a comparatively crude form of resonance vocoder. Supplementary equipment—the Peakpicker—is located between analyzer and synthesizer of the vocoder to carry out two functions, namely, to select spectrum channels containing voltage maxima and to establish connection from analyzer to synthesizer for the selected channels. All circuits of the vocoder proper are retained and used without change. The spectrum information to be transmitted can now be reduced, since at any moment only those channels are utilized in which voltage maxima are detected. The Peakpicker and an 18‐channel vocoder have been tested for selection of three, four, or five spectral maxima at sampling rates of 30 or 60 per sec. Under the best conditions thus far, nonsense syllable articulation scores in the 60% to 70% range have been realized, corresponding to high sentence intelligibility scores. It is estimated that this level of performance can be had with an over‐all information rate well below 1000 bits per second. Illustrative recordings will be presented. (This work was supported by the Department of Defense in connection with Contract DA49‐170‐se‐1642.)