Lower sideband modulation distortion cancellation
AssigneeOrban, Inc.
InventorRobert Orban
Life of this patent
Estimating the term…
Abstract
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.
Claims14
In an audio system that controls an input audio signal to provide a controlled audio signal, a method for cancellation of lower sideband modulation distortion comprising:
- generating a first signal which is a Hilbert transform of a signal associated with the control of the input audio signal;
- generating a second signal representative of a Hilbert transform of the input audio signal;
- multiplying the first signal and second signal to provide a third signal, and
- combining the third signal with the controlled audio signal.
The method defined by claims 1 or 3 wherein the signal associated with the control of the input audio signal is generated by:
- finding the vector sum of the input signal and the second signal and using a threshold level in association with the vector sum.
In an audio system where a control signal is used to control the gain of an audio signal to provide a controlled audio signal, a method for cancellation of lower sideband modulation distortion comprising:
- generating a first signal representative of the Hilbert transform of the control signal;
- multiplying the first signal and a second signal, the second signal representing the Hilbert transform of the audio signal, to provide a third signal;
- and
- combining at least part of the third signal with the controlled audio signal.
In a peak limiting apparatus, where an input audio signal (a) and the Hilbert transform signal (b) of the input audio signal are used to develop the signal z={square root over (a2+L +b2+L )}, and where z exceeds a predetermined threshold resulting in x and additionally where x is used to develop a control signal 1/x and, further where 1/x is multiplied with the input audio signal for peak limiting, an improvement comprising:
- a Hilbert transform means which receives the signal 1/x and provides an output signal;
- a multiplier for multiplying the output signal of the Hilbert transform means with the signal (b) to provide a third signal, coupled to the Hilbert transform means;
- and
- a combining means for combining the output of the multiplier with the third signal, coupled to the multiplier.
Dependencies are inferred from the claim text.