Digital equalizing filters with fixed phase response

摘要

An equalization filter structure for filtering an audio signal within an audio system is disclosed. The equalization filter comprises a first and a second shelving filter each 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. The first and the second shelving filters are coupled in series and each shelving filter comprises at least one fourth order low-pass filter having a cut-off frequency, a Q factor and a first broadband gain and further at least one fourth order high-pass filter having a second broadband gain and the same cut-off frequency and the same Q factor as the low-pass filter. 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. 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, and each second order filter has the same cut-off frequency and Q factor as the corresponding shelving filter.

主权项

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.