Unobtrusive removal of periodic noise
AssigneeFender Musical Instruments Corporation
InventorsDale Vernon Curtis, Charles Clifford Adams
Life of this patent
Estimating the term…
Abstract
An input signal is applied to a notch filter having a transfer function that is the inverse of the expected noise signal. The filtered signal is coupled to a first amplifier and the input signal is coupled to a second amplifier. The outputs of the amplifiers are summed. The gains of the amplifiers are oppositely adjusted in response to the magnitude of the input signal. At low amplitude, the filtered signal is amplified more than the unfiltered signal. At high amplitude, the unfiltered signal is amplified more than the filtered signal.
Claims9
Apparatus for unobtrusively removing a periodic noise signal from an input signal, said apparatus comprising:
- an input;
- a first channel coupled to said input and having an adjustable gain;
- a second channel having an adjustable gain coupled to said input;
- a detector coupled to said input for producing a control signal indicative of the energy of said input signal;
- said control signal causing the gain of the first channel and the gain of the second channel to vary inversely;
- and
- a notch filter in said second channel, said notch filter having at least one notch substantially at the fundamental frequency of said noise signal.
A method of unobtrusively removing a periodic noise signal from an input signal, said method comprising the steps of:
- (a) providing a first channel for the input signal;
- (b) providing a second channel for the input signal, wherein the second channel includes a notch filter having at least one notch substantially at the fundamental frequency of said noise signal;
- (c) coupling the input signal to both channels;
- and
- (i) passing the input signal through the first channel at high signal levels;
- and
- passing the input signal through the second channel at low signal levels;
- or
- (ii) passing the input signal through both channels at intermediate signal levels;
- wherein the first channel has an adjustable gain and the second channel has an adjustable gain and said method further includes the step of:
- varying the gain of the first channel inversely to the gain of the second channel.
A method of unobtrusively removing a periodic noise signal from an input signal, said method comprising the steps of:
- (a) providing a first channel for the input signal;
- (b) providing a second channel for the input signal, wherein the second channel includes a notch filter having at least one notch substantially at the fundamental frequency of said noise signal;
- (c) filtering the fundamental and harmonics of the noise signal from the second channel;
- (d) coupling the input signal to both channels;
- and
- (i) passing the input signal through the first channel at high signal levels;
- and
- passing the input signal through the second channel at low signal levels;
- or
- (ii) passing the input signal through both channels at intermediate signal levels;
- and varying the gain of the first channel in accordance with the magnitude of the input signal and varying the gain of the second channel inversely with the magnitude of the input signal.
Dependencies are inferred from the claim text.