Abstract: An improved method and apparatus is disclosed for perpendicularly mounting an AT-strip resonator on its longitudinal edge. The crystal blank is secured to the base at two or more mounting points via conductive cement which provides both electrical connection and mechanical support. A mounting cavity or slot permits proper positioning and self-fixturing during manufacture. The edge-mounting configuration promotes ease of manufacture, improved shock performance, minimized motional resistance degradation, and high packing density.

Abstract: An overload protection circuit is disclosed which limits the current supplied by a battery to a load. The circuit is particularly adapted for use in portable radio applications which must meet rigorous specifications of intrinsically safe equipment for use in hazardous environments. Load sensor 20 continuously monitors for the presence of load to enable power switch 16 via switch control 22. Current trip circuit 24 monitors the voltage developed across current sensor 18 to provide a disable signal to switch control 22 in the event of an overload condition. Current limit circuit 26 limits the drive signal to power switch 16. Voltage trip circuit 28 prevents overdissipation of the power switch device. Thus, intrinsically safe battery circuit 30 provides protection such that hazardous gases will not be ignited by sparks or thermal heating during overload conditions.

Abstract: An automatic gain selector is disclosed for use with a noise suppression system which performs speech quality enhancement upon a noisy speech signal available at the input to generate a noise-suppressed speech signal at the output by spectral gain modification. The channel gain controller (240) of the present invention produces a modification signal (245), comprised of individual channel gain values, for application to a channel gain modifier (250). A particular gain table set is automatically selected from one of a plurality of gain tables (450) by a selector switch (470) and a noise level quantizer (440) in response to a multi-channel noise parameter, such as the overall average background noise level of the input signal. Then the individual channel gain values (455) are obtained from the particular gain table set in response to the individual channel signal-to-noise ratio estimate (235).

Abstract: An improved background noise estimator (320) is disclosed for use with a noise suppression system (300) for generating an estimate of the background noise power spectral density provided to noise suppressor (310), which performs speech quality enhancement upon the pre-processed speech-plus-noise signal available at the input to generate a clean post-processed speech signal at the output. Background noise estimator (320) utilizes an energy valley detector based upon post-processed speech to perform the speech/noise classification, and a noise spectral estimator based upon pre-processed speech to generate an estimate of the background noise power spectral density. As a result, the background noise estimate supplied to the noise suppressor is a more accurate measurement of the background noise energy, since it is performed during a more accurate determination of the occurrences of pauses in the speech.

Abstract: An improved noise suppression system (400) is disclosed which performs speech quality enhancement upon speech-plus-noise signal available at the input (205) to generate a clean speech signal at the output (265) by spectral gain modification. The noise suppression system of the present invention includes a background noise estimator (420) which generates and stores an estimate of the background noise power spectral density based upon pre-processed speech (215), as determined by the detected minima of the post-processed speech energy level. This post-processed speech (255) may be obtained directly from the output of the noise suppression system, or may be simulated by multiplying the pre-processed speech energy (225) by the channel gain values of the modification signal (245). This technique of implementing post-processed signal to generate the background noise estimate (325) provides a more accurate measurement of the background noise energy since it is based upon much cleaner speech signal.

Abstract: A portable audio-visual demonstration apparatus which provides operational instruction and functional simulation or particularized electronic equipment for training and exhibition purposes is disclosed. The preferred embodiment of the invention is the application of the demonstration apparatus to communications equipment, specifically FM two-way mobile radios. This embodiment comprises: a plurality of actual radio control heads wherein all radio controls and functions are simulated to be fully operational; a display panel with overlying translucent forms which is illuminated to display the corresponding radio operational response; a tape deck which plays a cassette wherein voice instruction has been pre-recorded; and a portable hand-carried suitcase package which incorporates the above elements with its own power supply.