# US 7,613,608 B2 · Method and circuit for noise estimation, related filter, terminal and communication network using same, and computer program product therefor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,613,608 B2 - Document ID: US7613608B2 - Status: Granted - Kind: B2 - Application number: 10/579,058 - Filed: 2003-11-12 - Published: 2007-03-08 - Granted: 2009-11-03 - Earliest claimed: 2003-11-12 - Assignees: Telecom Italia S.p.A. - Inventors: Gianmario Bollano; Donato Ettorre; Rodrigo Pousas Navarro - Web page: https://patentgrep.com/patent/US7613608B2 ## CPC - G10L 21/0208: Noise filtering - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING ## Abstract A filter such as a Wiener filter for noise reduction in a signal, such as a speech signal, affected by background noise includes a circuit for determining values of an update function relating new value of estimated noise power to a previous value of estimated noise power, the update function being a function of said previous estimated noise power and a mean input power spectral density. The circuit includes a look-up table having values for the update function stored therein with the previous value of estimated noise power and the mean input power spectral density as a first and a second search entry, respectively. These search entries are entered via an input module and exploited by search circuitry associated with the look-up table for selectively searching values for the update function in the look-up table. The search is preferably carried out on the basis of an index computed starting from said first and second search entries. ## Claims ### Claim 1 A method of determining, in a noise reduction process applied to a signal affected by background noise, an update function relating a new value of estimated noise power (Pnoise—New) with a previous value of estimated noise power (Pnoise), said update function being a function of said previous estimated noise power (Pnoise) and a mean input power spectral density (Pin—PSD), comprising the steps of: providing a look-up table having stored therein values for said update function; determining a current value for said mean input power spectral density (Pin—PSD); and searching a corresponding value for said update function in said look-up table using said previous value of estimated noise power (Pnoise) and said current value for said mean input power spectral density (Pin—PSD) as a first and a second entry for said search. ### Claim 2 (depends on 1) The method of claim 1, comprising the steps of providing a look-up table having stored therein values for said update function, said update function being a function of a ratio of said mean input power spectral density (Pin—PSD) and said previous estimated noise power (Pnoise). ### Claim 3 (depends on 1) The method of claim 1, comprising the steps of performing said search in said look-up table based on an index computed starting from said first and second search entries. ### Claim 4 (depends on 1) The method of claim 1, wherein said values for said update function are stored in said look-up table as representative of a surface plotted against said first (x) and said second (y) entry, wherein said surface is partitioned in a plurality of regions each having a corresponding value for said update function, said constant value regions being separated by straight lines with known angular coefficients. ### Claim 5 (depends on 4) The method of claim 4, comprising the step of partitioning at least one portion of said surface in a plurality (2N) of angular regions, wherein said angular regions are selected from the areas between the straight lines: y=j·x/N when Pin—PSD=Pnoise wherein j is an integer from 1 to N, and wherein said first and second entries for the search are plotted on the x and the y-axis, respectively. ### Claim 6 (depends on 4) The method of claim 4, wherein said first and second entries are plotted on the x-axis and the y-axis, respectively, and comprises the steps of subdividing said surface into: a first portion between the line y =N.x and the x-axis, said first portion being subdivided on the basis of a linear approximation in a first plurality of regions wherein the lines partitioning said first plurality of regions define constant intervals therebetween at said x or y axis; and a second portion comprising the remaining portion of said surface, said second portion being subdivided on the basis of a linear approximation in a second plurality of regions wherein the lines partitioning said second plurality of regions are determined by the equation: y=NH·N·x/j wherein j is an integer from 1 to NH−1. ### Claim 7 (depends on 4) The method of claim 4, wherein said first and second entries are plotted on the x-axis and the y-axis, respectively, and comprises the steps of subdividing said surface into: a first portion between the line y =N.x and the x-axis, said first portion being subdivided on the basis of a linear approximation in a first plurality of regions wherein the lines partitioning said first plurality of regions define constant intervals therebetween at said x or y axis, and a second portion comprising the remaining portion of said surface, said second portion being subdivided on the basis of an exponential approximation in a second plurality of regions wherein the lines partitioning said second plurality of regions are determined by the equation: y=2j·N·x wherein j is an integer from 1 to NH. ### Claim 8 A circuit for determining, in a filter for noise reduction in a signal affected by background noise, an update function relating a new value of estimated noise power (Pnoise—New) with a previous value of estimated noise power (Pnoise), said update function being a function of said previous estimated noise power (Pnoise) and a mean input power spectral density (Pin—PSD), comprising: a look-up table having stored therein values for said update function; an input module for a current value for said mean input power spectral density (Pin—PSD); and search circuitry associated with said look-up table for selectively searching values for said update function in said look-up table using said previous value of estimated noise power (Pnoise) and said current value for said mean input power spectral density (Pin—PSD) as a first and a second entry for said search. ### Claim 9 (depends on 8) The circuit of claim 8, wherein said look-up table has stored therein values for said update function being a function of a ratio of said mean input power spectral density (Pin—PSD) and said previous estimated noise power (Pnoise). ### Claim 10 (depends on 8) The circuit of claim 8, wherein search circuitry associated with said look-up table is configured for performing said search in said look-up table on the basis of an index computed starting from said first and second search entries. ### Claim 11 (depends on 8) The circuit of claim 8, wherein said values for said update function are stored in said look-up table as representative of a surface plotted against said first (x) and said second (y) entries, wherein said surface in said look-up table is partitioned in a plurality of regions each corresponding to a given constant value for said update function, said constant value regions being separated by straight lines with known angular coefficients. ### Claim 12 (depends on 11) The circuit of claim 11, wherein said at least one portion of said surfaces comprises a plurality (2N) of angular regions, wherein said angular regions are selected from the areas between the straight lines: y=j·x/N when Pin—PSD=Pnoise wherein j is an integer from 1 to N, and wherein said first and second entries in the table are plotted on the x and the y-axis, respectively. ### Claim 13 (depends on 11) The circuit of claim 11, wherein said values for said update function are stored in said look-up table as representative of a surface plotted against said first (x) and said second (y) entries, wherein the surface in said look-up table is partitioned into: a first portion between the line y =N.x and the x-axis, said first portion being subdivided on the basis of a linear approximation in a first plurality of regions wherein the lines partitioning said first plurality of regions define constant intervals therebetween at said x or y axis; and a second portion comprising the remaining portion of said surface, said second portion being subdivided on the basis of a linear approximation in a second plurality of regions wherein the lines partitioning said second plurality of regions are determined by the equation: y=NH·N·x/j wherein j is an integer from 1 to NH−1. ### Claim 14 (depends on 11) The circuit of claim 11 wherein said values for said update function are stored in said look-up table as representative of a surface plotted against said first (x) and said second (y) entries, wherein the surface in said look-up table is partitioned into: a first portion between the line y =N.x and the x-axis, said first portion being subdivided on the basis of a linear approximation in a first plurality of regions wherein the lines partitioning said first plurality of regions define constant intervals therebetween at said x or y axis; and a second portion comprising the remaining portion of said surface, said second portion being subdivided on the basis of an exponential approximation in a second plurality of regions wherein the lines partitioning said second plurality of regions are determined by the equation: y=2j·N·x wherein j is an integer from 1 to NH. ### Claim 15 (depends on 8, 9, 10, 11, 12, 13, 14) A filter comprising a circuit according to any one of claims 8-14 for estimating noise power. ### Claim 16 (depends on 15) The filter of claim 15, wherein said filter is a Wiener filter. ### Claim 17 (depends on 15) A mobile terminal comprising a filter according to claim 15, for noise reduction of speech signal. ### Claim 18 (depends on 17) A communication network comprising a mobile terminal according to claim 17. ### Claim 19 (depends on 1, 2, 3, 4, 5, 6, 7) A computer readable medium encoded with a computer program product loadable into a memory of at least one computer and comprising software code portions for performing the method of any one of claims 1-7.