# US 9,438,195 B2 · Variable equalization > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,438,195 B2 - Document ID: US9438195B2 - Status: Granted - Kind: B2 - Application number: 14/502,997 - Filed: 2014-09-30 - Published: 2015-11-26 - Granted: 2016-09-06 - Earliest claimed: 2014-05-23 - Assignees: Apple Inc. - Applicants: Apple Inc. - Inventors: Arvindh Krishnaswamy; Joseph M. Williams - Web page: https://patentgrep.com/patent/US9438195B2 ## CPC - H03G 5/165: {Equalizers; Volume or gain control in limited frequency bands} - H03G 5/005: {of digital signals} - H03G: CONTROL OF AMPLIFICATION ## Abstract An equalizer that linearly interpolates between two equalization states when transitioning from one equalization state to the other equalization state is described. The equalizer includes a transfer function generator and an equalization module. Each equalization state is defined or determined based on a set of parameters. The transfer function generator generates a set of interpolated transfer functions by performing linear interpolation on a first equalization state and a second equalization state based on the set of parameters. The linear interpolation is performed on corresponding Z-domain poles and zeros of the transfer functions of the first and second equalization states. The equalization module applies the set of interpolated transfer functions generated by the transfer function generator to an input audio signal. ## Claims ### Claim 1 An audio processor comprising: a transfer function generator that is to generate a set of interpolated transfer functions by performing linear interpolation on a first equalization state and a second equalization state, wherein the linear interpolation is performed on corresponding Z-domain poles and zeros of transfer functions of the first and second equalization states; and an equalization module that is to apply the set of interpolated transfer functions generated by the transfer function generator to an input audio signal. ### Claim 2 (depends on 1) The audio processor of claim 1, wherein performing the linear interpolation on corresponding Z-domain poles and zeros of the transfer functions of the first and second equalization states comprises: for each pole of the transfer function of the first equalization state, performing linear interpolation on the pole and a corresponding pole of the transfer function of the second equalization state; and for each zero of the transfer function of the first equalization state, performing linear interpolation on the zero and a corresponding zero of the transfer function of the second equalization state. ### Claim 3 (depends on 2) The audio processor of claim 2, wherein the performing of linear interpolation on two poles comprises performing linear interpolation on radius of the two poles and performing linear interpolation on angle of the two poles. ### Claim 4 (depends on 2) The audio processor of claim 2, wherein the performing of linear interpolation on two zeros comprises performing linear interpolation on radius of the two zeros and performing linear interpolation on angle of the two zeros. ### Claim 5 (depends on 1) The audio processor of claim 1, wherein the linear interpolation generates a set of interpolated equalization states. ### Claim 6 (depends on 5) The audio processor of claim 5, wherein each of the set of interpolated transfer functions corresponds to an interpolated equalization state of the set of interpolated equalization states. ### Claim 7 (depends on 6) The audio processor of claim 6, wherein the equalization module is to apply the set of interpolated transfer functions in a sequence in which the set of interpolated equalization states gradually transition from the first equalization state to the second equalization state. ### Claim 8 (depends on 1) The audio processor of claim 1, wherein the equalization module is further to apply transfer functions of the first equalization state and the second equalization state. ### Claim 9 (depends on 1) The audio processor of claim 1, wherein each equalization state is defined based on a set of parameters, wherein the linear interpolation is performed based on the set of parameters. ### Claim 10 A method for audio equalization comprising: for an input audio signal, receiving a request to change from a first equalization filter to a second equalization filter; performing linear interpolation on the first equalization filter and the second equalization filter to generate a set of interpolated equalization filters between the first and second equalization filters, wherein the linear interpolation is performed on corresponding Z-domain poles and zeros of the first equalization filter and the second equalization filter; and applying the set of interpolated equalization filters to the input audio signal. ### Claim 11 (depends on 10) The method of claim 10, wherein the method further comprises constructing the set of interpolated equalization filters using the interpolated poles and zeros. ### Claim 12 (depends on 10) The method of claim 10, further comprising determining the Z-domain poles and zeros for the first and second equalization filters. ### Claim 13 (depends on 10) The method of claim 10, wherein the performing of linear interpolation on corresponding Z-domain poles and zeros of the first and second equalization filters comprises: for each pole of the first equalization filter, performing linear interpolation on the pole and a corresponding pole of the second equalization filter; and for each zero of the first equalization filter, performing linear interpolation on the zero and a corresponding zero of the second equalization filter. ### Claim 14 (depends on 13) The method of claim 13, wherein the performing of linear interpolation on two poles comprises performing linear interpolation on radius of the two poles and performing linear interpolation on angle of the two poles. ### Claim 15 (depends on 13) The method of claim 13, wherein the performing of linear interpolation on two zeros comprises performing linear interpolation on radius of the two zeros and performing linear interpolation on angle of the two zeros. ### Claim 16 (depends on 10) The method of claim 10 further comprising: receiving the input audio signal; applying the first equalization filter to the input audio signal; and applying the second equalization filter to the input audio signal. ### Claim 17 (depends on 10) The method of claim 10, wherein each equalization filter is determined based on a set of parameters, wherein the linear interpolation is performed based on the set of parameters. ### Claim 18 (depends on 10) The method of claim 10, wherein the set of interpolated equalization filters are applied in a sequence in which the set of interpolated equalization filters gradually transition from the first equalization filter to the second equalization filter.