A noise control system includes: a control sound generator for generating a control sound; an error detector for detecting an error signal between the control sound and noise; a noise detector for detecting a noise source signal; an adaptive filter for outputting a control signal; and a coefficient updator for updating a coefficient of the adaptive filter. The coefficient updator includes at least a first digital filter, a first coefficient update calculator, a second digital filter, a phase inverter, a third digital filter, and a second coefficient update calculator. Alternatively, the coefficient updator includes at least a first digital filter, a second digital filter, a third digital filter, a coefficient update calculator, a phase inverter, a first adder, and a second adder. In either case, the coefficient updator has a function of suppressing an increase in a coefficient gain of the adaptive filter in a predetermined frequency band.

Noise control system

A signal enhancement system improves the understandability of speech or other audio signals. The system reinforces selected parts of the signal, may attenuate selected parts of the signal, and may increase SNR. The system includes delay logic, a partitioned adaptive filter, and signal reinforcement logic. The partitioned adaptive filter may track and enhance the fundamental frequency and harmonics in the input signal. The partitioned filter output signals may approximately reproduce the input signal, delayed by an integer multiple of the period of the fundamental frequency of the input signal. The reinforcement logic combines the input signal and the filtered signals to produce an enhanced output signal.

Periodic signal enhancement system

An adaptive equalizer comprises a decision device; a decision feedback equalizer coupled to the decision device; an FIR filter coupled to the decision device; and a trellis decoder coupled to the decision device, adapted to provide a reliability output and a decoded output. An error signal is generated by subtracting an output of the decision feedback equalizer from an output of the decision device, the error signal being used to update coefficients of the taps of the FIR filter and the decision feedback equalizer. A magnitude of the change to the coefficients is selected based at least in part the reliability output of the trellis decoder.

Adaptive equalizer having a variable step size influenced by output from a trellis decoder

A coefficient updating method stops updating filter coefficients for a plurality of adaptive filters when a convergence condition is achieved. Active noise control within a system simulates an original noise signal with a simulated noise signal which is equal and opposite to the original noise signal. To detect feedback in such a system, a reference signal or "white noise" is generated by a speaker, transmitted through the system and received by a microphone. Coefficients of multiple filters such as an anti-feedback filter, a C filter, and a noise control filter are then updated to minimize adverse parameters such as original noise and feedback. Coefficient updating of the adaptive filters is stopped when a minimum average value is reached.

Coefficient updating method for an adaptive filter

An active adaptive control system introduces a control signal from an output transducer (14) to combine with the system input signal (6) and yield a system output signal (8). An error transducer (16) senses the system output signal and provides an error signal (44). An adaptive filter model (40) has a model input from a reference signal (42) correlated to the system input signal, and an output outputting a correction signal (46) to the output transducer to introduce the control signal according to a weight update signal (74) provided by the product (from multiplier 72) of the reference signal and the error signal. Selective leakage of the weight update signal is provided in response to a given condition of a given parameter, preferably output power of the correction signal, to control performance of the model, to selectively degrade same according to need. Leakage is varied by multiplying a previous weight update value by a factor γ and adding the result to the product of the reference signal and error signal, and varying γ as a function of the correction signal.

Active adaptive control system with weight update selective leakage

A main adaptive digital filter and a sub adaptive digital filter are provided, and these two adaptive digital filters share a filter coefficient to be controlled. On the side of the main adaptive digital filter, the shared coefficient is updated so that the difference between the output and a desired response is minimized and on the side of the subadapted digital filter, the above-stated shared filter coefficient is updated so that the output is minimized. A prescribed limitation is given to the frequency characteristic of a filter coefficient to be adapted, by treating the input of the sub adaptive digital filter as a signal weighted on the frequency or a noise having its band limited with respect to the input signal or the output signal of the main adaptive digital filter, and coefficient updating control is conducted so that the coefficient will not go beyond the limitation.

Masaki Eguchi

Papers

System using plurality of adaptive digital filters