Orban Associates, Inc.

Other

Akg Acoustics Gmbh

Orban, Inc.

Kurt Orban Company

Robert A Orban

A method for computing the 'clippings' of an audio signal in the digital domain to prevent aliasing is disclosed. An offset signal is found by subtracting a threshold from samples of the audio signal. These are multiplied by a pulse after the pulse is lined up in time with the crossing of the audio signal at the threshold. The pulse is the sum of two step functions, both of which are bandwidth-limited.

Anti-aliased clipping by band-limited modulation with step functions

A feedback controller, embedded in an FM audio processor, that controls the &ldquo;integrated multiplex power&rdquo; to the requirements of ITU-R 412 (2.51) is disclosed. This regulation specifies the maximum power, which is the same as the power produced by a sinewave modulating the carrier &plusmn;19 kHz (where &plusmn;75 kHz is 100% peak modulation). The controller applies the square of the multiplex signal to an integrator. A constant is removed from the integrator; representing the maximum power threshold. The output of the integrator is sampled periodically with a sample-and-hold circuit. A second integrator receives the output of the sample-and-hold. The output of the second integrator circuit is added to the threshold setting of a compressor, which determines the average power output of the compressor. The output of the compressor is applied through a peak controller to the input of the multiplex coder, closing a feedback loop, which controls the integrated multiplex power to a preset threshold.

Controller for FM 412 multiplex power regulation

A method for controlling the peak levels of an FM composite signal is described. First, the FM signal is clipped to obtain an error signal. This signal comprises the &ldquo;clippings&rdquo; resulting from the clipping operation. Next, the peaks of the error signal are determined. Then, a half-cosine wave is fitted to each of the peaks. The resultant half-cosine-interpolated signal is filtered to provide a filtered error signal. This error signal is subtracted from the FM composite signal.

Controlling the peak levels of the FM composite signal by half-cosine interpolation

A digital clipper is highly oversampled to decrease aliasing and increase accuracy. The difference between the clipper's input and output is then downsampled and added to the delayed, unclipped signal at 1&times; sample rate to achieve clipping. Filters operating at 1&times; can be placed in series with the downsampled differentially-clipped signal to achieve overshoot compensation, bandlimiting of the clipped signal, and other goals.

Oversampled differential clipper

An audio peak limiter in which the lower sideband of the modulation distortion spectrum is canceled. The peak limiter is realized by multiplying the input signal by a control signal. The Hilbert transform of the control signal is multiplied by the Hilbert transform of the input signal and the outputs of the two multipliers are added. This cancels the lower sideband of the modulation process. Various filters can be added to eliminate aliasing in digital realizations, to band-limit the output signal, and to control peak overshoot.

Lower sideband modulation distortion cancellation

An audio peak limiter suitable for use between a compressor and pre-emphasis circuit. The limiter uses a center clipper to develop a control signal for a 1/x control law VCA. The center clipping, after rectification, is sampled-and-held for 4 milliseconds by a retriggerable sample-and-hold circuit then low-pass filtered. The compressed audio is delayed for 4 milliseconds before being coupled to the VCA. The VCA acts as a modulator to provide control of its peak output level while simultaneously limiting the bandwidth of the modulation sidebands caused by the modulation process, so that these sidebands are better masked psychoacoustically than sidebands that would be caused by simple clipping of the compressed audio.

Multi-band audio compressor with look-ahead clipper

Two level detectors with logarithmic outputs receive an input audio signal. The first level detector receives the signal through a high-pass filter while the second level detector receives the signal through a band-pass filter contoured to simulate the equal-loudness curves of the human ear. The difference between the detectors' outputs (representing the log of the ratio of their respective input levels) is processed to provide quick broadband gain reduction whenever the ratio exceeds a preset threshold, providing de-essing. The difference is further smoothed and then applied to a voltage-controlled high-pass filter that provides high-frequency boost, the amount of which is controlled by the relative high frequency power contained within the input signal. This voltage-controlled high-pass filter applies automatic, program-adaptive equalization to the input signal.

Combined de-esser and high-frequency enhancer using single pair of level

An audio compressor having both a feedback compressor and a feedforward compressor. The feedback compressor operates so as to provide envelope detection. A sidechain processor which receives an input from the feedback path includes a non-linear low-pass filter and a non-linear amplifier. The output of this processor provides the gain-control signal for the feedforward compressor. The main audio path is through the feedforward compressor.

Audio compressor combining feedback and feedfoward sidechain processing

Audio equalizer circuit for adjusting the amount of boost and cut. The circuit uses a combination negative feedback, positive feedback, negative feed-forward and positive feed-forward resulting in boost and cut characteristics which are entirely reciprocal and which, nonetheless provides an infinite-depth notch. The equalizer is fabricated with an ordinary band pass filter, resistors, potentiometer and operational amplifiers.

Audio equalizer providing reciprocal equalization plus infinite-depth

Apparatus for reducing distortion in a peak limited audio siganl. The amount of low-frequency spectral energy in the input audio signal is determined for a peak limited signal and used to control low-frequencies in the output audio signal. Identical low-pass filters with cut-off frequencies of 2.2 kHz are used; one passing a peak limited signal, the other a non-peak limited signal. When no noticeable low-frequency spectral energy is present in the peak limited (clipped) signal, the peak level is controlled below 2.2 kHz, without distortion, by a VCA and above 2.2 kHz by a clipper. When low-frequency spectral energy is present, the VCA reduces gain on each low-frequency wave to prevent uncontrolled safety clipping.

Distortion-cancellation circuit for audio peak limiting

An audio processor consisting of a 'single-ended' dynamic noise reduction system cascaded and cross-coupled with a program-adaptive dynamic equalizer. The audio at the output has a consistent subjective spectral texture even if the spectral texture of the input audio varies widely. Further, although the system often adds high frquency energy to the audio, it does not increase the perceived noise level and is free from audible noise modulation.

Dynamic noise reduction and spectral restoration system

An audio equalization circuit for use in an AM transmission system is described which is particularly useful for compensating for the high frequency rolloff found in currently manufactured AM receivers. A single potentiometer adjustment in the feedback path of the equalization circuit allows the response in the AM receiver to be effectively and economically adjusted.

Adjustable equalizer for compensating for high frequency rolloff and

A circuit for providing enhanced stereophonic sound by processing the L-R signal. A compressor which receives the L+R signal provides a gain control signal. This signal controls the level of the L-R signal and the gain in a tracking VCA. The tracking VCA receives the enhanced L-R signal and under predetermined conditions prevents increasing the level of the L-R signal.

Stereophonic image widening circuit

Improved FMX Companding apparatus for FM transmitter. A pilot subsystem which is substantially identical to the FMX audio path is used to develop a control signal which provides amplitude control through a VCA in the main FMX audio path.

Encoding for the FMX companding system

A peak limiter is described which employs the Hilbert transform. Effectively distinct processing occurs for low frequency and high frequency signals and harmonic distortion results only when the limiter is excited by high frequencies.

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Belmont, CA, United States of America

Robert A Orban