Amplitude Contour Display of Sound Spectrograms
A. J. Prestigiacomo · The Journal of the Acoustical Society of America · 1962
Sound spectrographs typically displayed complex signals, such as speech, on teledeltos (facsimile) paper with frequency and time plotted along the ordinate and abscissa, and shades of gray to indicate the relative intensity of the frequency components. The gray scale is usually limited by the teledeltos paper to a marking range of 12 dB, whereas the signal may have amplitude variations of 40 to 50 db. A voltage quantizer has been designed which will plot equal-level contours in the frequency/time plane. The equal-level plateaus were selected at 6-dB intervals over a 42-db range. Gray-scale compression is also obtained as a by-product of this quantizer to shade each contour level such that a 42-dB change in signal level causes a 12-dB change in marking voltage. A discussion of the design and operating principles is given so that one can incorporate the circuit into a spectrograph or modify the circuit for other applications.