John F. Holzrichter

Speech articulator measurements using low power EM-wave sensors.

Very low power electromagnetic (EM) wave sensors are being used to measure speech articulator motions as speech is produced. Glottal tissue oscillations, jaw, tongue, soft palate, and other organs have been measured. Previously, microwave imaging (e.g., using radar sensors) appears not to have been considered for such monitoring. Glottal tissue movements detected by radar sensors correlate well with those obtained by established laboratory techniques, and have used to estimate a voiced excitation function for speech processing applications. The noninvasive access, coupled with the small size, low power, and high resolution of these new sensors, permit promising research and development applications in speech production, communication disorders, speech recognition and related topics.

Voiced excitation functions calculated from micropower impulse radar information

Efforts underway at the Lawrence Livermore National Laboratory to use newly designed micropower impulse radars (MIR) to measure in real time the excitation function of the vocal tract will be presented. Studies undertaken in collaboration with the University of California at Davis and the University of Iowa with high‐speed laryngoscopic cameras, electroglottographs, flow masks, and subglottal pressure transducers have solidified the relationship between the signal returned by the MIR and the voiced excitation function of the vocal tract. As a result, for the first time a transfer function of the vocal tract can be calculated in real time and with unprecedented clarity for voiced speech. This new capability could have significant implications for improvements in speech recognition and speech synthesis processing.

Comparison of conventional acoustic and MIR radar/acoustic processing of speech signals

Applications of the micropower impulse radar (MIR) to speech research at the Lawrence Livermore National Laboratory has produced potentially new methods of speech processing. They include the accurate calculation of vocal tract transfer functions, formant, and pitch analysis, and basic phoneme synthesis. These speech parameters have traditionally been in the realm of all‐pole LPC calculations. Related research using the MIR radar has supplied an increasingly accurate voiced excitation function, which makes possible transfer function calculations using both poles and zeros, yielding more accurate formant information and more natural sounding synthesis. This paper compares the newly obtained results with traditional LPC and cepstral approaches and demonstrates the improvements based on experimental data from several male and female subjects. The radar data also allow extremely accurate pitch tracking, which is simpler and more robust than that calculated by traditional means. This information can significan...

Highly efficient thermophotovoltaics enabled by photon re-use

Thin-film photovoltaic cells with high reflectivity in the below-bandgap spectral region are ideally suited for thermophotovoltaics. This allows the below-bandgap radiation to be reflected back to the emitter, so that their energy can be used to reheat the source, rather than being lost. In this work, we present a substantial improvement in the theoretical thermophotovoltaic conversion efficiency in the presence of photon re-use. We also predict the achievable conversion efficiency for a system that uses In0.53Ga0.47As photovoltaic cells, and present an experimental optical cavity to be used for future efficiency measurements. Owing to recent advances in thin-film photovoltaics, thermophotovoltaic efficiencies above 50% may soon be realizable.

Speaker verification performance comparison based on traditional and electromagnetic sensor pitch extraction

This work compares the speaker verification performance between a traditional acoustic‐only pitch extraction to a new electromagnetic (EM) sensor based pitch approach system. The pitch estimation approach was developed at the Lawrence Livermore National Laboratory (LLNL) utilizing Glottal Electromagnetic Micropower Sensors (GEMS, also see http://speech.llnl.gov/). This work expands previous pitch detection work by Burnett et al. [IEEE Trans. Speech and Audio Processing (to be published)] to the specific application of speaker verification using dynamic time warping. Clearly, a distinct advantage of GEMS is its insensitivity to acoustic ambient noise. This work demonstrates the clear advantage of the GEMS pitch extraction to improve speaker verification error rates. Cases with added white noise and other speech noise were also examined to show the strengths of the GEMS sensor in these conditions. The EM sensor speaker verification process operated without change over signal‐to‐noise (SNR) conditions rangin...