Patent ID: 8687819

Claim:
A method of estimating ambient noise in a listening system, the listening system comprising an input transducer for converting an input sound to an electrical input signal, including picking up an ambient noise, and an output transducer for converting an electrical output signal to an output sound, an electrical forward path being defined between the input transducer and the output transducer and providing a forward gain |G(f)|, f being frequency, the listening system further comprising an electrical feedback path comprising an adaptive filter for estimating an acoustic feedback gain |H(f)| from the output transducer to the input transducer, the adaptive filter comprising a variable filter part and an algorithm part, the variable filter part providing an estimate of the acoustic feedback path based on filter coefficients hâ€²(i,nNT s ) determined by the algorithm part, where each i=0, 1, 2, . . . , M represents one tab of the impulse response with the filter order of M at the specific instance in time nNT s at the measurement iteration n, the method comprising a) monitoring an energy Îº M (nNT s ) of a first-difference of the filter coefficients hâ€²(i,nNT s ) over time; and b) applying a predefined threshold criterion to the change in energy content from one time instance to another to determine an acceptable impact of the ambient noise, wherein the energy Îº M (nNT s ) of the first-difference of the filter coefficients over time is calculated at a time instance nNT s , where T s is a sampling period, N is an integer, and Îº M â¡ ( n â¢ â¢ N â¢ â¢ T s ) â‰¡ 1 4 â¢ â¢ âˆ‘ i = 0 M â¢ ï˜ƒ h â€² â¡ ( i , n â¢ â¢ N â¢ â¢ T s ) - h â€² â¡ ( i , ( n - 1 ) â¢ N â¢ â¢ T s ) ï˜„ 2 â¢ â¢ âˆ‘ i = 0 M â¢ h â€² â¡ ( i , n â¢ â¢ N â¢ â¢ T s ) 2 - âˆ‘ i = 0 M â¢ h â€² â¡ ( i , ( n - 1 ) â¢ N â¢ â¢ T s ) 2 ï˜ƒ âˆ‘ i = 0 M â¢ h â€² â¡ ( i , n â¢ â¢ N â¢ â¢ T s ) 2 - âˆ‘ i = 0 M â¢ h â€² â¡ ( i , ( n - 1 ) â¢ N â¢ â¢ T s ) 2 ï˜„ , where M is the order of the AFC filter hâ€²(i,nNT s ).