摘要:
Dynamic range modifying circuits, namely compressors and expanders, are disclosed in which series connected circuits respond to current or voltage drive to provide voltage or current output. One circuit has characteristics which do not vary with dynamic range and contributes a component to the output having dynamic range linearity relative to the input. A second circuit has variable impedance characteristics and contributes a component which does not have dynamic range linearity relative to the input and which effects the dynamic range modification. Devices are described in which the variable impedance characteristics include effective negative resistance which is itself varied and is shunted by a variable reactance. Devices are also described in which the second circuit is a two terminal network which responds to the current between the two terminals to determine the voltage therebetween and wherein the voltage is derived either by way of a variable filter which acts to restrict the voltage or by way of multiple paths including filters and limiters.
摘要:
Compressor and expander circuits are constructed by combining the outputs of two circuit paths, both connected to an input terminal. The combining is effected by a variable combining means which responds to a signal level in the circuit to vary the proportions in which the two circuit paths contribute to the output signal.
摘要:
A noise masking compandor for greatly reducing the noise added to a wide dynamic range audio signal in passing through a noisy channel, such as a tape recorder. The audio signal, having a dynamic range of approximately 90 db, is compressed to a dynamic range of approximately 30 db for transmission through the noisy channel then subsequently expanded in a complementary fashion to its original 90 db range to provide a faithful reproduction of the original signal without noticeable noise. Compression and expansion result from high precision rectifiers to minimize distortion, and are further achieved without the need for maintaining precisely constant input and output levels for the noisy channel to avoid frequency response distortion. A high degree of high and low frequency signal preemphasis is provided in the compression and expansion characteristic without creating overload problems for the noisy channel.
摘要:
A circuit is added to a loudspeaking telephone for preventing the telephone form locking in its receive mode in response to high-amplitude received noise whenever the volume control is adjusted to a high setting. This additional circuit controls a variable impedance device of a receiving channel of the telephone without affecting a variable impedance of a transmitting channel thereof. The circuit increases loss in the receiving channel when the amplitude of translated received noise is greater than the amplitude of translated received noise is greater than the amplitude of translated received speech. The increased loss is switched out of the receiving channel when the amplitude of translated received speech exceeds the amplitude of translated received noise.