Other

Dorrough Electronics

Michael L Dorrough

Kenneth S Gold

H Maurice France

Michael J Cane

Dennis Robert Lee

Richard Williamson Burden

Alfred Edward Parker

Robert R Conger

In an AM system directed to commercial broadcasting, a pure unmodulated (CW) carrier signal and two sideband signals are generated and processed separately as three independent signals that are summed as output of a final linear mixer. The sideband signals are derived independently utilizing audio spectrum-sharing based on complementary comb filtering, quadrature phase-shifting at both audio and carrier sideband frequencies, and exclusive alternate toggling at a designated switching rate between the two sidebands so that at any instant in time only one of the two sidebands is present along with the continuous carrier. The overall performance provides the capability of advantageous modulation beyond the conventional 100% modulation limit.

Amplitude modulation with time- and spectrum-shared sidebands

In this micro-controller-based line voltage meter/monitor instrument, an AC signal-under-test is sensed from the line voltage via a broadband isolation transformer, and processed to provide RMS and fast peak signals. These are A/D converted in the micro-controller in a sampling process synchronized from a zero-cross signal detected from the AC voltage-under-test. An LED (light-emitting diode) display with 40 LED segments provides resolution of one volt RMS per LED step/segment, and is color-coded to overlay the CBEMA nominal limits. RMS values ranging from 95 to 135 volts are indicated on a bar graph, and fast peak values ranging from 120 to 500 volts at the waveform crest are indicated by the selected LED cell flashing at a 1 Hz rate, with selectable peak hold time. An internal real time calendar/clock enables accumulation of time-related data regarding the ongoing quality of the power line voltage levels. A variety of parameters and alarm limits can be configured by the user via a DIP switch and/or a user port, accessible at the rear of the instrument, by which the instrument can be connected in two-way communication with an external computer or control terminal, e.g. with a keyboard and/or CRT monitor, to provide a variety of extended capabilities.

Power line meter/monitor with LED display

For professional audio operations such as recording and broadcasting, an LED bar-graph display instrument monitors average and peak loudness levels of stereophonic audio signals that have been encoded in serial digital format such as AES/EBU digital audio format. Internal audio processing circuitry, that can be implemented digitally with a custom chip gate array set, receives as input a serial stream of digital stereo audio data and converts this to ballistically conditioned logarithmic average and peak levels which are simultaneous displayed, generally simulating the ballistics of contemporary standard electronically displayed loudness meters such as the Dorrough analog model. The peak hold can be switched manually or internally between three hold durations: indefinite, 3 seconds or zero. A preferred dual embodiment provides digital implementation driving a pair of LED bar-graph displays side-by-side in vertical or horizontal orientation for stereo applications, and provides selectable display of stereo signals or sum and difference signals. A special peak capture circuit ensures that even very narrow peak levels are indicated at full amplitude despite the controlled ballistic rise rate. Over-range is indicated by a color change of three top display segments.

Level meter for digitally-encoded audio

A two channel audio switcher includes two analog switches, which may be implemented as a CMOS integrated circuit, receiving at their control input ports a complementary pair of drive signals, typically square wave, so as to toggle their outputs at a supersonic rate, which may be made variable. The switcher may receive as input two channels of a stereophonic source, two independent audio sources or a common monophonic source. The outputs typically drive an audio output unit such as the transmitter of a radio broadcasting system, an audio recording system, or amplifiers, controls and loudspeakers of a sound reinforcement system in an auditorium or studio. The system may be monophonic or stereophonic. In a stereophonic a.m. broadcasting system such as the Kahn independent sideband system, alternate switching allows each sideband to be modulated to full available power, thus allowing an increase in the apparent radiated power. In audio recording, the switcher prevents peak levels of each channel from summing instantaneously and thus enables an increase in the effective recorded level on each channel. In a sound system where the source includes one or more microphones, an auxiliary microphone is made to provide intentional feedback to one channel of the switcher, providing flexibility in processing the toggled feedback to break up standing waves to suppress system feedback 'howl', thus increasing the usable acoustic power and improving auditorium coverage.

Sequential audio switcher

For monitoring, metering and dynamically displaying key static and dynamic parameters of composite video signals and visually indicating compliance status relative to important system specifications, this electronic meter is particularly useful in connection with video cameras. In studio environments, the compliance indications supplement existing capabilities, and in remote locations where large, complex and costly CRT type waveform monitors are not feasible, the compactness of this video meter provides an unusual degree of picture quality assurance. A bar/graph type LED display provides two independent scale regions: a sync region dynamically displaying sync amplitude, and a picture region dynamically displaying average picture levels in a bar mode and peak levels in a dot mode. The response times of the sync, average and peak level are selectable. Peak indications are lengthened to a display time which is optimal for human response to short term events. A monochrome video meter embodiment displays average luminance levels in a bar mode and peak luminance levels in a dot mode. Presence/absence of sync is indicated by a bi-color LED. Additional parameter status may be indicated by a panel-mounted bi-color LED which provides four indication modes. For color video, a chrominance embodiment, used along with the monochrome embodiment and similarly packaged, displays color burst amplitude and average chrominance in a bar mode, peak chrominance in a dot mode, and optionally monitors color burst phase relative to horizontal sync.

Dynamic video luminance and chrominance meter

A dual loudness meter and method for simultaneously indicating the apparent loudness of composite audio program material representing peak material or of persistent material employing a first detector means responsive to peak signals for instantaneously indicating the same as a singly actuated LED indicator in an array thereof displayed in accordance with the peak strength of the signal, a second detector for detecting the persistence of the signal and displaying the same as a bar graph on said LED display, the materials being colinearlly displayed and having dual upper extreme warning/operating indicator means separated by about 12 to 14 dB so that the meter is read as requiring adjustment of the associated recording or broadcast facilities to avoid having either of said programming indicator displays reading consistently in either warning/operating zone. Specific circuits and time constants of response and decay are given as appropriate to the simultaneous reading, dual meter system disclosed.

Growing community of inventors

Woodland Hills, CA, United States of America

Michael L Dorrough