Patent ID: 8077880

Claim:
A method for equalizing audio signals, the method comprising: processing an input signal through a low frequency equalization path comprising: low pass filtering the input signal to obtain a low pass filtered signal; sub sampling the low pass filtered signal to obtain a sub-sampled signal; equalizing the sub-sampled signal with a low frequency equalization filter F(z) to obtain an equalized low frequency sub-sampled signal, the low frequency equalization filter F(z) computed by the steps: low pass filtering a Loudspeaker Room Transfer Function (LRTF) H(z); sub sampling the filtered LRTF H(z); computing the low frequency equalization filter F(z) from the sub sampled filtered LRTF H(z); up sampling the low frequency equalization filter F(z) to obtain a high sample F′(z); computing C(z) as the product of the high sample F′(z) and the LRTF H(z); computing the magnitude of C(z); and computing a mean level L1 of the magnitude of C(z); up sampling the equalized low frequency sub-sampled signal to obtain an up-sampled low frequency equalized signal; and low pass filtering the up-sampled low frequency equalized signal to obtain a low frequency equalized signal; processing the input signal through a high frequency equalization path comprising: high pass filtering the input signal to obtain a high pass filtered signal; and equalizing the high pass filtered signal with a high frequency equalization filter G(z) to obtain a high frequency equalized signal, the high frequency equalization filter G(z) computed by the steps: high pass filtering the LRTF H(z); computing an initial high frequency equalization filter G(z) from the high pass filtered LRTF H(z); computing D(z) as the product of the initial high frequency equalization filter G(z) and LRTF H(z); constraining FFT bins of the D(z) below fs/2M to 0 dB; computing a mean level L2 of the constrained magnitude; and applying a level adjustment of 10 ((L1-L2)/20) to the initial G(z) to obtain the high frequency equalization filter G(z); and summing the low frequency equalized signal and the high frequency equalized signal to obtain an equalized signal.