Active noise control classification system
Methods of classifying and using acoustic filters for active noise control in hearing systems, such as headphones. The acoustic filters are determined and stored in a memory in the hearing system, making it therefore possible to quickly and efficiently select and use a certain filter in order to improve filter performance and filter stability in the hearing system.
1 . A method for classifying and applying filters for active noise control in a hearing system having at least one feedforward microphone and at least one feedback microphone, at least one loudspeaker, at least one integrated circuit comprising a memory and at least one processor unit, at least one feedback audio path described by a feedback transfer function and at least one feedforward path described by a feedforward transfer function, comprising the steps of:
a) receiving a first audio signal that is a feedback microphone signal at the at least one feedback microphone, and receiving a second audio signal that is a feedforward microphone signal at the at least one feedforward microphone;
b) estimating the feedback transfer function by an adaptive algorithm based on a comparison of the feedback microphone signal and a loudspeaker signal;
c) calculating at least one of a plurality of relevant properties from the estimated feedback transfer function;
d) determining a level at the at least one feedback microphone in relation to a level at the at least one feedforward microphone;
e) selecting, by a classifying algorithm, a set of filter coefficients based on the calculated relevant properties of the estimated feedback transfer function and the determined level of the at least one feedback microphone, either by outputting a discrete class assigned to a set of filters stored on the memory of the hearing system or by outputting a one-dimensional function that selects a set of filters stored on the memory of the hearing system;
f) applying the selected set of filter coefficients as a feedback filter in a current feedback audio path;
g) estimating the feedforward transfer function by comparing the received feedforward signal and the received feedback microphone signal using an adaptive algorithm to estimate the feedforward transfer function;
h) calculating at least one of a plurality of the relevant properties from the estimated feedforward transfer function;
i) determining a performance indicator by referencing the received feedback microphone signal to the feedforward microphone signal;
j) selecting a second set of filter coefficients using the calculated relevant properties of the estimated feedforward transfer functions of step h) and the determined performance indicator of step i) as inputs of a classifying algorithm which uses them to select the second set of filter coefficients, either by outputting a discrete class associated with a set of filters stored on the memory located in the hearing system, or by outputting a one-dimensional function which selects a set of filters stored on the memory located in the hearing system;
k) applying the second set of filter coefficients as a feedforward filter in a current feedforward audio path; and
l) Readjusting the feedback filter and the feedforward filter by performing steps a)-k) again, or readjusting only the feedforward filter by performing steps g)-k) again.
2 . The method of claim 1 , wherein after the feedback microphone signal has been received, the feedback microphone signal is pre-filtered.
3 . The method of claim 1 , wherein after reception of the feedforward microphone signal by the feedforward microphone, the feedforward microphone signal is pre-filtered.
4 . The method of claim 1 , wherein after an initial adjustment of the feedback filter and the feedforward filter, a gain of the feedback filter and/or the feedforward filter can be adjusted.
5 . The method of claim 4 , wherein the level at the at least one feedback microphone and/or the determined performance indicator is used to determine an ideal filter gain for a selected wearing situation.
6 . The method of claim 5 , wherein a default filter is defined for the active noise control of the hearing system, which is used when a sensor sensitivity of the hearing system falls below a predefined threshold value.
7 . The method of claim 5 , wherein one or more feedback filters and feedforward filters are arranged hierarchically sorted by class in a filter matrix as a function of shape and gain on the memory of the hearing system.
8 . The method of claim 1 , wherein one or both of the feedback microphone signal and the feedforward microphone signal is prefiltered by a high-pass, low-pass, or band-pass filter.