Patent ID: 9257953
Filing Date: 2016-02-09
CPC Classification: H03G,H03H,H04S

Claim Text:
1. An equalization filter structure for filtering an audio signal within an audio system, the equalization filter comprising: a first and a second shelving filter having a fixed first and a fixed second phase response, each of which is determined by a respective cut-off frequency and Q factor which represent the transfer characteristic of the corresponding shelving filter; wherein the first and the second shelving filters are coupled in series and each shelving filter comprises (i) at least one fourth order low-pass filter having a cut-off frequency, the Q factor and a first broadband gain and (ii) at least one fourth order high-pass filter having the same cut- off frequency and the same Q factor as the low-pass and further having a second broadband gain; wherein the fourth order low-pass filter and the fourth order high-pass filter are connected in parallel, such that both filters receive the same input signal and the corresponding filtered signals are summed to form a respective shelving filter output signal; and wherein each fourth order low-pass and high-pass filter is composed of a cascade of two second order low-pass or high-pass filters, respectively, each second order filter having the same cut-off frequency and the Q factor as the corresponding shelving filter.