PubMed · 4787945
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C D Stamopoulos. 1973. A pulse audio modulator.. https://doi.org/10.1007/bf02478676
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A targeting-and-extracting procedure of speech enhancement for hearing aids in the presence of background noise, especially competing speech, is proposed. The procedure is composed of two steps: targeting by a fixed (or deterministic) beamforming array, followed by a post-targeting extracting step. Emphasis is placed on the extracting step, which performs noise cancellation based on the acoustic difference between the desired speech and interfering speech. Either comb filtering or attenuation is applied to the signal in accordance with the current voiced/unvoiced/silence state of the desired signal. The comb filter design is based on the fundamental pitch frequency of the desired speech. Algorithms for deciding the voiced/unvoiced/silence state and determining the fundamental frequency are developed. The performance of the system is evaluated through computer simulation. The simulation results indicate significant noise cancellation and intelligibility improvement.
The relationship between localization and the Franssen effect was studied for noise and tones in a sound-deadened and in a live room. The noise was wideband and the tones were 250, 500, 1000, 1500, 2500, and 4000 Hz. Listeners were asked to determine the location of the stimuli in a localization task and to discriminate the difference between a pair of stimuli used to generate the Franssen illusion and a steady-state tone in a Franssen-effect discrimination task. Poor performance in the Franssen-effect discrimination task is consistent with the stimulus conditions leading to a strong Franssen illusion. Poor performance in both the Franssen effect and localization tasks was obtained for midfrequency tones (near 1500 Hz) and in the live room. Thus, the Franssen illusion is strongest for a live room and for midfrequency tones consistent with the difficulty listeners have in localizing sounds under these conditions. These results are consistent with those of Hartmann and Rakerd [J. Acoust. Soc. Am. 86, 1366-1373 (1989)] and support their suggestion of a correlation between the Franssen effect and localization in rooms.
A novel light source for the near-infrared region which has the highest intensity and widest spectral bandwidth of all near-IR light sources has been developed. The system is based on a single-mode fiber (about 18 m long) doped with Er3+ ion. The doped ion produces amplified spontaneous emission (ASE) in the near-IR region (from 1500 to 1600 nm) when it is excited by a diode laser at 980 nm. Because the diode laser is fusion-spliced directly to the doped fiber, the system is compact, all-solid-state, reliable, and stable and requires little maintenance. Its ASE output intensity was found to be comparable with those of diode lasers currently available for this near-IR region and is much higher than those of conventional halogen-tungsten lamps and the so-called (high-intensity) superluminescent light emitting diodes (SLEDs). Its spectral bandwidth is, however, much wider than those of the diode lasers and the SLEDs. Even higher intensity can be obtained from the doped fiber when a low-intensity (1 mW) light from a 1550-nm laser diode is introduced into the doped fiber. The intensity is enhanced (up to 7 times compared to the ASE) because the input light is amplified by the doped fiber. Furthermore, the output intensity of this erbium-doped fiber amplifier (EDFA) can be appropriately adjusted to provide relatively higher output intensity at any range of wavelengths (within this 1500-1600-nm region) by simply changing the temperature and/or the driven current of the input diode laser. Subsequently, an acoustooptic tunable filter was used to provide a means to spectrally tune the EDFA rapidly and to develop an all-solid-state, compact near-IR spectrophotometer which not only is very sensitive, stable, and reliable but also has a very high throughput. This spectrophotometer can detect water in ethanol at a limit of detection of 10 ppm. More importantly, the high through-put makes it possible to use the instrument to measure spectra of highly absorbing samples (e.g., absorption spectrum of 1.0 M Pr3+ aqueous solution through four sheets of paper); measurements which are currently not possible with halogen-tungsten lamp-based spectrophotometers.