Spectral Match Research Articles

Laser-beam characteristics of Phoenix, an HF oscillator-amplifier system

Energy-extraction and beam-quality measurements are reported for Phoenix, Sandia’s high-energy HF laser system. The final amplifier in this oscillator-amplifier chain used electron-beam initiation of high-pressure gas mixtures of H2-F2-O2. The oscillator and preamplifier utilized fast electric discharges in SF6-HI mixtures. Energy-extraction efficiency using this oscillator system was the same as that previously determined using an H2-F2-O2-fueled oscillator which produced a better spectral match to the amplifier but which yielded poorer beam quality. Lateral shearing interferograms showed no significant phase-front degradation of the beam by the final amplifier. Pinhole energy-transmission measurements using a short-focal-length parabolic mirror determined that the focal-spot diameter was 2.7 times the diffraction-limited diameter.

Computer identification of infrared spectra by correlation-based file searching

A new method for the computerized search and identification of infrared spectra has been developed and evaluated. Based on cross-correlation, the search system utilizes all spectral information in a digitized spectrum when it attempts to match an unknown spectrum to one in a small library of known spectra. To evaluate a spectral match, the search program calculates the cross-correlation function between the unknown and known (library) spectra which indicates their degree of similarity and allows library spectra to be ranked in order of probability of match to the unknown spectrum. In this study, several small infrared spectral libraries of structurally similar compounds were searched under conditions which examined the sensitivity of the search method to chemical and instrumental variations. Because the correlation technique is slower than conventional file-searching methods, it will probably find greatest use in the search of small collections of similar spectra or as a match-ranking procedure following preliminary selection by a faster search method.

Wind instrument very-nearfield and room-average spectra

Woodwind and brass instruments radiate their lower-frequency components isotropically. At higher frequencies (above the tone-hole or bell-propagation cut-off frequency) each component is radiated in its own highly directional pattern which complicates measurement of overall spectral envelopes, even in a reverberant room. A microphone placed at the first open hole of a woodwind receives a rapidly convergent series of contributions from the lower holes. It is shown that both above and below the tone-hole cut-off frequency (≃ 1500 Hz for clarinet or oboe) the spectrum recorded by this microphone is very nearly the same as that obtained by spectral averaging of sounds recorded at many points in the room. Similar results are obtained for spectra obtained with a microphone placed one bell radius in front of a brass instrument bell. Despite the spectral match, the perceived tore color of nearfield recordings differ from those based on simple room averages, and from ordinary room listening. The auditory mechanism appears to be sensitive to early-echo spectral subtleties associated with the differing angular distribution of low and high frequency components. Implications for psychoacoustics, for recorded conventional music, and for electronically generated music will be discussed.

Formant tracking algorithm for a speech analysis-synthesis system

A formant tracking algorithm has been developed to provide control signals automatically for a parallel formant speech synthesizer. In voiced sounds, the algorithm first estimates positions of high-energy excitation in the sampled speech waveform to be analyzed. These positions generally correspond to the points of glottal closure, and the interval following each position should correspond to a closed glottis region. For each such position the speech samples in the following few milliseconds are used to calculate a log power spectrum. An analysis-by-synthesis procedure iteratively updates estimates of formant frequencies and amplitudes using spectral matching criteria. A similar spectral-matching procedure is used during unvoiced sounds, but time averaging is introduced as appropriate when deriving the spectra to be matched. To cope with situations when the formant structure is not clearly defined in the power spectrum the iteration is performed separately for several different allocations of formants to spectral peaks. A final choice of formant frequencies and amplitudes is made every 10 msec and depends on both goodness of spectral match and continuity of formant tracks. Demonstrations will be made of the speech quality achieved for a number of male talkers.

The use of up-converter phosphors in semiconductor light-emitting devices and displays

Infrared-emitting semiconductor diodes have proved to be useful sources for exciting up-converter phosphors. Diodes made from silicon-doped GaAs have proved to be the most useful sources at present. The diode-phosphor system is discussed in terms of spectral match between diode output and phosphor excitation, design of diode geometry, enhancement of visible output by the use of pulsed operation, and multicolor operation. Currently maximum reported efficiencies range from 6 × 10−5 to 10−3 for various phosphors.

The Electroluminescent Panel as a Binary Light Source

The most readily available and least expensive device used to expose very small areas on film, as required for experiments in image processing, has been found to be the electroluminescent panel (EP). This device has several characteristics that are highly advantageous for use in replacing a tungsten light source and a shutter. The EP luminance output is a function of both the ac driving voltage and frequency and can be turned on and off very rapidly. The EP is available in different spectral emission ranges, allowing flexibility in its use; also the spectral emission can be shifted by driving the EP for a specific application. The spectral output, with reference to how it is affected by driving voltage and frequency, is discussed and the spectral match between the film and the EP is shown. Photographs are used to show in detail the results of the EP binary light source and how it has been used in image processing.

Coherent amplification characteristics of a GaAs phased array

The coherent amplification properties of antireflective coated GaAs diodes are considered for application to a phased array amplification scheme. The developmemt and design characteristics of a ten-element array system are discussed. An experimental diode array possessing good electrical and spectral match among diodes and excellent thermal dissipation is shown to provide optical gains, for main master laser modes, of at least 13 dB per array diode after coating. Temporal and spatial coherence within a GaAs laser spot, approximately 35 µ wide, is found to be adequate for array amplification purposes. The effects of array amplification on an incident coherent beam are evaluated by comparing predicted fringe patterns with observed interference patterns. The coherence of the incident beam is shown to be preserved during the amplification process.

Analysis of Acoustic Speech Signals into Articulatory Parameters

An analysis technique is discussed whereby speech spectra are compared with spectra generated by a computer-simulated model of articulation. In this model, a spectrum is determined by specifying as input parameters a vocal-tract area function (or a simplified configurational description) and the source spectral envelope and location. The input parameters are adjusted to obtain a “spectral match” between the internally generated spectrum and the speech spectrum, thereby specifying the articulatory parameters that correspond to the given speech spectrum. Data relating to matches from several classes of speech sounds are presented. Questions pertaining to the uniqueness and applicability of the parameters obtained by this procedure are discussed, with particular reference to descriptions of vocal-tract dynamics. The possibility of using parameters derived by this technique to control a dynamic vocal-tract analog synthesizer is also considered. [This work was supported in part by the U. S. Army, the U. S. Air Force Office of Scientific Research, and the U. S. Office of Naval Research; in part by the U. S. Air Force (Electronic Systems Division) under Contract AF 19(604)-6102; in part by the National Science Foundation (Grant G-16526); and in part by the National Institutes of Health (Grant MH-04737-02).

The United States Color Standards for Rosin

The new official United States color standards for grading gum rosin are described and compared with the superseded 1923 Lovibond glass standards. The new standards are made of cemented combinations of Jena and Corning glasses, and show a better spectral match with rosin, higher luminous transmission, more regular spacing of colors on a chromaticity scale, and are more solidly constructed than the old standards. Spectral transmission curves for rosins and the glass standards are shown. The standard colors are specified in terms of the 1931 I.C.I. colorimetric coordinate system with its standard observer and standard illuminant C. Chromaticity tolerances are established for duplicate standards.