Abstract: An RF-type amplification system, such as a classroom amplification system, employs technology adapted from a cordless telephone system to overcome interference. The amplification system includes a portable remote unit (87) and a base unit (82). Remote unit (87) includes: a microphone (151) for detecting a voice and generating corresponding voice signals; a transmitter (160, 161) which generates RF signals containing the voice signals as well as control signals provided by the central processing unit (179) of remote unit (87), and an antenna (168) for transmitting the RF signals and for receiving RF signals from base unit (82). Base unit (82) includes an antenna (107) which receives the RF signals transmitted by the remote unit and a receiver (108, 114, 115, 117) which detects the RF signals and separates the RF signals into the voice signals and control signals. The control signals are identified by a code detector (118) of base unit (82) and evaluated by a CPU (130).

Abstract: Improved signal to noise ratio to help speech comprehension in a noisy environment is accomplished by selectively downwardly expanding a speech and noise composite signal when the speech signal is absent, thereby lowering signal components which represent noise. An expansion control signal is extracted from the composite input signal. Operation is based on the assumption that when noise alone is present, the input signal amplitude is less than some reference level and that when speech and noise are present together, the input signal amplitude is greater than the reference level. The response rates of gain changes are quite rapid, and do not introduce distortion or other audibly noticeable artifacts of the processing. The amount of downward expansion of the noise alone is small compared to noise gates to further reduce processing artifacts.

Abstract: Inexpensive wideband transducers convert low frequency components (i.e., approximately 50 Hz through 800 Hz) of an audio signal to mechanical vibrations at the same frequencies so that the vibrations may be perceived at the user's skin, typically at a hand or finger. The transducer may be a small permanent magnet moving coil loudspeaker with most of the diaphragm cone removed to minimize soundwave generation, or it may be a small d.c. or stepping motor arranged to have its drive shaft rotated in alternate directions through small angles corresponding to signal amplitude. Vibrations may be applied to the user's hand through a hand-held case vibrating with the motor, or to a finger via a contactor extending outside the case from the motor or loudspeaker. The transducer has particular utility in conjunction with closed captioned in television programs to enhance appreciation of speech therein while also training the user in utilizing the transducer.

Abstract: Directional hearing in noisy environments is enhanced using small conventional microphones. In one embodiment a conventional first order bidirectional gradient microphone is employed in connection with a barrier to produce sound shadow at the rearward end of the microphone. In other embodiments such as hearing assistive devices worn on a person's head or body, the head or body of that person serves as the barrier. The result is a significant reduction in gain for all frequencies of acoustic energy emanating from generally rearward of the microphone. The sound shadow creates an apparent change of direction of arrival for rearwardly arriving acoustic energy, thereby making it appear to the microphone that the sound is approaching from the high attenuation 90.degree. direction. Two spaced bidirectional microphones worn on a person's body may be positioned to take advantage of this effect while simulating binaural hearing in an assistive listening device.

Abstract: A circuit for suppressing background noise of a continuous nature while enhancing speech signals, or signals having the transient temporal qualities of speech, includes a signal multiplier which, in the preferred embodiment, receives the composite audio signal along with a control signal present only when the speech component of the audio signal is present. The control signal may be derived from an AGC circuit having a slow attack, fast decay characteristic to establish a quiescent output level from the AGC amplifier in the absence of speech. An envelope detector is biased to provide a zero output amplitude in response to the quiescent amplifier output level. Speech components appearing in the amplifier output signal are then envelope-detected and filtered to provide the control signal. Alternatively, the control signal can be derived by envelope-detecting the audio signal, filtering the detected signal to remove its d.c. component representing the continuous noise, and then detecting and filtering again.