# US 12,114,137 B2 · Filters and filter chains > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,114,137 B2 - Document ID: US12114137B2 - Status: Granted - Kind: B2 - Application number: 18/524,887 - Filed: 2023-11-30 - Published: 2024-03-28 - Granted: 2024-10-08 - Earliest claimed: 2021-10-05 - Assignees: Cirrus Logic, Inc. - Applicants: Cirrus Logic International Semiconductor Ltd. - Inventors: John P. Lesso - Web page: https://patentgrep.com/patent/US12114137B2 ## CPC - H04R 3/04: for correcting frequency response - H04R 1/32: for obtaining desired directional characteristic only {(specially adapted for hearing aids H04R25/40)} - H04R 2430/03: Synergistic effects of band splitting and sub-band processing - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract An apparatus, comprising: an audio input for receiving an input audio signal; an tuning input for receiving a tuning signal; a filter chain comprising a plurality of filters for filtering the audio signal to produce a filtered input audio signal, the filter chain comprising: a first filter module operating at a first sampling rate; and a second filter module operating at a second sampling rate greater than the first sampling rate, wherein a phase response of the first filter module is dependent on the tuning input and wherein a magnitude response of the first filter module is substantially independent of the tuning input. ## Claims ### Claim 1 An audio filter system comprising: an oversampled filter chain, the filter chain comprising a plurality of audio filter modules, wherein a first filter module of the plurality of audio filter modules running at a lowest sample rate of the chain is arranged to receive a tuning signal and to adjust the phase response of the first filter module based on the tuning signal such that pre-ringing and/or post-ringing of the filter chain is varied. ### Claim 2 (depends on 1) The audio filter system of claim 1, comprising: an audio input for receiving an input audio signal; and a tuning input for receiving the tuning signal; wherein the oversampled filter chain is configured to filter the audio signal to produce a filtered input audio signal, wherein the first filter module is configured to operate at a first sampling rate, wherein the plurality of audio filter modules comprises a second filter module operating at a second sampling rate greater than the first sampling rate, and wherein a magnitude response of the first filter module is substantially independent of the tuning signal. ### Claim 3 (depends on 1) The audio filter system of claim 1, wherein, in response to a change in the tuning signal, the first filter module is configured to transition between having a linear phase response and having a minimum phase response. ### Claim 4 (depends on 2) The audio filter system of claim 2, wherein, in response to an increase in the tuning signal, the first filter module is configured to: increase the level of pre-ringing in the filtered input signal due to the filter chain; and decrease the level of post-ringing in the filtered input signal due to the filter chain increases. ### Claim 5 (depends on 1) The audio filter system of claim 1, wherein a second filter module of the plurality of filter module comprises a decimation filter, wherein the first filter module is provided after the second filter module in the filter chain. ### Claim 6 (depends on 1) The audio filter system of claim 1, wherein a second filter module of the plurality of filter module comprises an interpolation filter, wherein the first filter module is provided before the second filter module in the filter chain. ### Claim 7 (depends on 1) The audio filter system of claim 1, wherein the first filter module comprises: a plurality of first filters for generating respective first filtered signals, the plurality of first filters each having a different phase response; and a multiplexer configured to switch between respective first filtered signals for output based on the tuning signal. ### Claim 8 (depends on 7) The audio filter system of claim 7, wherein the first filter module comprises: a pre-filter for generating a pre-filtered signal, wherein the plurality of first filters are configured to generate the respective first filtered signals based on the pre-filtered signal. ### Claim 9 (depends on 8) The audio filter system of claim 8, wherein the pre-filter comprises a minimum phase filter or a linear phase filter. ### Claim 10 (depends on 7) The audio filter system of claim 7, wherein the plurality of first filters each comprise an all-pass filter having a different phase response. ### Claim 11 (depends on 7) The audio filter system of claim 7, wherein during switching between respective first filtered signals the multiplexer is configured to output a weighted combination of two or more of the respective first filtered signals. ### Claim 12 (depends on 7) The audio filter system of claim 7, wherein the multiplexer is configured to switch between respective first filtered signals for output during a zero-crossing point of the input signal or during a period in which the input signal is below a signal threshold. ### Claim 13 (depends on 1) The audio filter system of claim 1, wherein the first filter module comprises: a first filter for generating a first filtered signal; and a second filter for filtering the first filtered signal to generate a second filtered signal, wherein a response of the second filter is dependent on the tuning signal. ### Claim 14 (depends on 13) The audio filter system of claim 13, wherein the second filter is an all-pass filter or wherein the second filter is adjustable between minimum phase and linear phase based on the tuning signal. ### Claim 15 (depends on 13) The audio filter system of claim 13, wherein an impulse peak in a response of the second filter is substantially independent of the tuning signal, and wherein pre-ringing and post-ringing of the second filter vary in dependence on the tuning signal. ### Claim 16 (depends on 13) The audio filter system of claim 13, wherein the first filter is of the same order as the second filter. ### Claim 17 (depends on 1) The audio filter system of claim 1, further comprising: a tuning module configured to adapt the first filter module based on a characteristic of an audio system comprising the audio filter system. ### Claim 18 (depends on 17) The audio filter system of claim 17, wherein the characteristic of the audio system comprises one of: a type of audio output device comprised in the audio system; a type of amplifier comprised in the audio system. ### Claim 19 (depends on 1) An integrated circuit comprising the audio filter system of claim 1, wherein the tuning input is coupled to one or more pins of the integrated circuit. ### Claim 20 (depends on 1) An audio playback device comprising the audio filter system of claim 1, wherein the audio playback device comprises a high fidelity (Hi-Fi) stereo system. ### Claim 21 (depends on 1) A digital to analog converter (DAC) system comprising the audio filter system of claim 1. ### Claim 22 A filter module comprising: a first filter configured to receive an input signal and provide a first filtered signal, and a second filter configured to receive the first filtered signal and provide a second filtered signal as an output signal, wherein the first and second filters present a combined filter response for the filter module, the second filter arranged to receive a tuning signal and dynamically adjust a level of pre-ringing of the filter module based on the tuning signal, while maintaining a substantially constant magnitude response of the filter module. ### Claim 23 A filter module comprising: a first filter configured to receive an input signal and provide a first filtered signal, a plurality of second filters configured to receive the first filtered signal and provide a plurality of second filtered signals, the plurality of second filters having different phase responses, and a multiplexer configured to receive the plurality of second filtered signals and provide an output signal selected from the plurality of second filtered signals, wherein the first filter and the selected second filter present a combined filter response for the filter module, wherein the multiplexer is arranged to receive a tuning signal and to select one of the plurality of second filtered signals to be output based on the tuning signal.