Deltalab Research, Inc.

Analog and Digital Systems, Inc.

Hybrid Systems Limited

Audio Pulse, Inc.

Richard E DeFreitas

Samuel Wilensky

Daniel T Sullivan

Peter W Mitchell

John J Blake

Peter D Tribeman

Joseph L Boucher

Generating clock signals of slightly different frequencies without the signals locking up in synchrony, by providing a voltage-to-frequency converter driven by the output of an integrator, which is supplied with a signal representative of the sum of a frequency-difference command and the difference in frequency between the two clocks.

Generating narrowly-separated variable-frequency clock signals

Delta encoding circuitry of the type in which a digitally-encoded signal is determined by the difference between a present value of an input signal and a reconstructed signal representative of a past value of said input signal. The occurrence of a high or a low state in the digitally-encoded signal corresponds to an incremental change in the input signal of an amount dependent upon a reference signal determined from said digitally-encoded signal. The reference signal is increased by a positive-feedback circuit upon detection of one or more consecutive repetitions of the same digital state in the digitally-encoded signal.

Digital encoding circuitry

In an electrical system for generating a digitally-encoded signal from an analog signal and a reference signal, a circuit for reducing quantization noise comprises a bandpass filter which passes audible frequency components, the output of which filter is used to adjust the encode signal so as to reduce the level of audible components in a signal decoded from the encoded one.

Digital encoding circuitry with means to reduce quantization noise

In an electrical system of the type in which a digitally encoded signal is determined at least in part by the difference between a present value of an input signal and a reference signal representative of a past value of the input signal, improved circuitry for generating the reference signal. The improved circuitry comprises extraction means including a filter for extracting from the pattern of bits in the digitally encoded signal information relating to the time derivative of the present value of the input signal and an envelope detector for processing the output of the filter to provide a control signal, and integrating means responsive to the control signal to provide the reference signal.

Circuitry for generating reference signal for delta encoding systems

Apparatus for extracting recorded natural ambience from two audio channels while eliminating the cave-like quality of the sound of a soloist or announcer. The two channels are combined such that signals common to the two channels in a midrange of audio frequencies are cancelled, and the combined signal is time delayed.

Reproducing multichannel sound

In an electrical system of the type in which a digitally-encoded signal is determined at least in part by the difference between a present value of an input signal and a reconstructed signal representative of a past value of the input signal and including a filter for extracting from the digital signal information relating to the time derivative of the input signal, peak detection means for determining the peak value of the output of said filter, and a signal generating means responsive to a reference signal determined from the output of said peak detection means for generating the reconstructed signal, improved circuitry for generating the reference signal. The circuit comprises weighting means for increasing the magnitude of the input to the filter as a function of the preponderance of one or the other state in said digitally-encoded signal.

In an electrical system of the type in which a digitally encoded signal is determined at least in part by the difference between a present value of an input signal and a reference signal representative of a past value of the input signal, improved circuitry for generating the reference signal. The improved circuitry comprises extraction means including a filter for extracting from the pattern of bits in the digitally encoded signal information relating to the time derivative of the present value of the input signal to provide a corresponding control signal, and integrating means responsive to the control signal to provide the reference signal.

Enclosure for high fidelity audio reproduction equipment

An audio system which achieves a concert hall reverberation effect from a stereo input signal. From two stereo input signals the audio system produces quadraphonic signals suitable for application to four speakers in the pattern of a quadraphonic sound reproduction system. The system applies the stereo input signals to a front pair of speakers substantially without alteration while reverberation is added to the stereo input signals for application to the rear speakers which realistically reproduces the impression of concert hall acoustics in the sound reaching the listener from all four speakers. The reverberation is provided by a channel signal delay scheme in combination with a channel interconnection network which achieves long reverberation times with a high echo density that eliminates objectionable, discrete echo effects.

Simulation of reverberation in audio signals

A delta-sigma converter and corresponding decoder employing predetermined characteristics of readily available logic elements. The converter is realized through the use of an integrator responding to an analog input signal and a dual D flip-flop package having a high impedance, comparator functioning input and low impedance output to act as a switch to control the integrator. Switching of the flip-flop acts to provide pulses at a rate corresponding to the analog input signal level.

Growing community of inventors

Westford, MA, United States of America

Richard E DeFreitas