# US 2008/0189103 A1 · Signal Distortion Elimination Apparatus, Method, Program, and Recording Medium Having the Program Recorded Thereon > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2008/0189103 A1 - Document ID: US20080189103A1 - Status: Published application - Kind: A1 - Application number: 11/913,241 - Filed: 2007-02-16 - Published: 2008-08-07 - Earliest claimed: 2006-02-16 - Assignees: Nippon Telegraph and Telephone Corporation - Inventors: Takuya Yoshioda; Takafumi Hikichi; Masato Miyoshi - Web page: https://patentgrep.com/patent/US20080189103A1 ## CPC - G10L 21/0208: Noise filtering - G10L 2021/02082: {the noise being echo, reverberation of the speech} - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING ## Abstract Provided is a signal distortion elimination apparatus comprising: an inverse filter application means that outputs the signal obtained by applying an inverse filter to an observed signal as a restored signal when a predetermined iteration termination condition is met and outputs the signal obtained by applying the inverse filter to the observed signal as an ad-hoc signal when the predetermined iteration termination condition is not met; a prediction error filter calculation means that segments the ad-hoc signal into frames and outputs a prediction error filter of each frame obtained by performing linear prediction analysis of the ad-hoc signal of each frame; an inverse filter calculation means that calculates an inverse filter such that a concatenation of innovation estimates of the respective frames becomes mutually independent among their samples, where the innovation estimate of a single frame (an innovation estimate) is the signal obtained by applying the prediction error filter of the corresponding frame to the ad-hoc signal of the corresponding frame, and outputs the inverse filter; and a control means that iteratively executes the inverse filter application means, the prediction error filter calculation means and the inverse filter calculation means until the iteration termination condition is met. ## Claims ### Claim 1 A signal distortion elimination apparatus that eliminates signal distortion of an observed signal to obtain a restored signal, said signal distortion elimination apparatus comprising: an inverse filter application means that applies, when a predetermined iteration termination condition is met, a filter (hereinafter referred to as an inverse filter) to said observed signal and outputs the results thereof as said restored signal, and applies, when said iteration termination condition is not met, said inverse filter to said observed signal and outputs the results thereof as an ad-hoc signal; a prediction error filter calculation means that segments said ad-hoc signal into frames, and outputs a prediction error filter of each of said frames obtained by performing linear prediction analysis on said ad-hoc signal of each frame; an inverse filter calculation means that calculates said inverse filter such that the samples of a concatenation of innovation estimates of said respective frames (hereinafter referred to as an innovation estimate sequence) become mutually independent, where said innovation estimate of a single frame (hereinafter referred to as an innovation estimate) is the signal obtained by applying said prediction error filter of the corresponding-frame to the ad-hoc signal of the corresponding frame, and outputs the inverse filter; and a control means that iteratively executes said inverse filter application means, said prediction error filter calculation means and said inverse filter calculation means until the iteration termination condition is met. ### Claim 2 (depends on 1) The signal distortion elimination apparatus according to claim 1, wherein: said prediction error filter calculation means is configured to perform linear prediction analysis on the ad-hoc signal of each frame in order to calculate either a prediction error filter that minimizes the sum of the variances of said respective innovation estimates over all said frames or a prediction error filter that minimizes the sum of the log variances of said respective innovation estimates over all said frames, and outputs said prediction error filter for each frame; and said inverse filter calculation means is configured to calculate an inverse filter that maximizes the sum of the normalized kurtosis values of said respective innovation estimates over all said frames as said inverse filter that makes said samples of said innovation estimate sequence become mutually independent, and outputs this inverse filter. ### Claim 3 (depends on 1) The signal distortion elimination apparatus according to claim 1, wherein: said prediction error filter calculation means is configured to perform linear prediction analysis on the ad-hoc signal of each frame in order to calculate either a prediction error filter that minimizes the sum of the variances of said respective innovation estimates over all said frames or a prediction error filter that minimizes the sum of the log variances of said respective innovation estimates over all said frames, and outputs said prediction error filter for each frame; and said inverse filter calculation means is configured to calculate, as said inverse filter that makes said innovation estimate sequence become mutually independent, either an inverse filter that minimizes the sum of the variances of said respective innovation estimates over all said frames or an inverse filter that minimizes the sum of the log variances of said respective innovation estimates over all said frames, and outputs this inverse filter. ### Claim 4 A signal distortion elimination apparatus that eliminates signal distortion of an observed signal to obtain a restored signal, said signal distortion elimination apparatus comprising: a whitening filter calculation means that outputs a whitening filter obtained by performing linear prediction analysis on said observed signal; a whitening filter application means that outputs a whitened signal by applying said whitening filter to said observed signal; an inverse filter application means that applies, when a predetermined iteration termination condition is met, a filter (hereinafter referred to as an inverse filter) to said whitened signal and outputs the results thereof as said restored signal, and applies, when said iteration termination condition is not met, said inverse filter to said whitened signal and outputs the results thereof as an ad-hoc signal; a prediction error filter calculation means that segments said ad-hoc signal into frames, and outputs a prediction error filter of each of said frames obtained by performing linear prediction analysis on said ad-hoc signal of each frame; an inverse filter calculation means that calculates said inverse filter such that the samples of a concatenation of innovation estimates of said respective frames (hereinafter referred to as an innovation estimate sequence) become mutually independent, where said innovation estimate of a single frame (hereinafter referred to as an innovation estimate) is the signal obtained by applying said prediction error filter of the corresponding frame to the ad-hoc signal of the corresponding frame, and outputs the inverse filter; and a control means that iteratively executes said inverse filter application means, said prediction error filter calculation means and said inverse filter calculation means until said iteration termination condition is met. ### Claim 5 (depends on 1, 2, 3, 4) The signal distortion elimination apparatus according to any of claims 1 to 4, wherein: said iteration termination condition is that the number of iterations is R1, where R1 is an integer satisfying R1≧1. ### Claim 6 (depends on 1, 2, 3, 4) The signal distortion elimination apparatus according to any of claims 1 to 4, wherein: said observed signal is a speech signal including signal distortion. ### Claim 7 A signal distortion elimination method for eliminating signal distortion of an observed signal to obtain a restored signal, said signal distortion elimination method comprising: an inverse filter application step wherein an inverse filter application means applies, when a predetermined iteration termination condition is met, a filter (hereinafter referred to as an inverse filter) to said observed signal and outputs the results thereof as said restored signal, and applies, when said iteration termination condition is not met, said inverse filter to said observed signal and outputs the results thereof as an ad-hoc signal; a prediction error filter calculation step wherein a prediction error filter calculation means segments said ad-hoc signal into frames, and outputs a prediction error filter of each of said frames obtained by performing linear prediction analysis on said ad-hoc signal of each frame; and an inverse filter calculation step wherein an inverse filter calculation means calculates said inverse filter such that the samples of a concatenation of innovation estimates of said respective frames (hereinafter referred to as an innovation estimate sequence) become mutually independent, where said innovation estimate of a single frame (hereinafter referred to as an innovation estimate) is the signal obtained by applying said prediction error filter of the corresponding frame to the ad-hoc signal of the corresponding frame, and outputs the inverse filter; and a control step wherein a control means iteratively executes said inverse filter application steps, said prediction error filter calculation steps and said inverse filter calculation steps until said iteration termination condition is met. ### Claim 8 (depends on 7) The signal distortion elimination method according to claim 7, wherein: said prediction error filter calculation step is adapted to perform linear prediction analysis on the ad-hoc signal of each frame in order to calculate either a prediction error filter that minimizes the sum of the variances of said respective innovation estimates over all said frames or a prediction error filter that minimizes the sum of the log variances of said respective innovation estimates over all said frames, and outputs said prediction error filter for each frame; and said inverse filter calculation step is adapted to calculate an inverse filter that maximizes the sum of the normalized kurtosis values of said respective innovation estimates over all said frames as said inverse filter that makes said innovation estimate sequence become mutually independent, and outputs this inverse filter. ### Claim 9 (depends on 7) The signal distortion elimination method according to claim 7, wherein: said prediction error filter calculation step is adapted to perform linear prediction analysis on the ad-hoc signal of each frame in order to calculate either a prediction error filter that minimizes the sum of the variances of said respective innovation estimates over all said frames or a prediction error filter that minimizes the sum of the log variances of said respective innovation estimates over all said frames, and outputs said prediction error filter for each frame; and said inverse filter calculation step is adapted to calculate, as said inverse filter that makes said innovation estimate sequence become mutually independent, either an inverse filter that minimizes the sum of the variances of said respective innovation estimates over all said frames or an inverse filter that minimizes the sum of the log variances of said respective innovation estimates over all said frames, and outputs this inverse filter. ### Claim 10 A signal distortion elimination method for eliminating signal distortion of an observed signal to obtain a restored signal, said signal distortion elimination method comprising: a whitening filter calculation step wherein a whitening filter calculation means outputs a whitening filter obtained by performing linear prediction analysis on said observed signal; a whitening filter application step wherein a whitening filter application means outputs a whitened signal by applying said whitening filter to said observed signal; an inverse filter application step wherein an inverse filter application means applies, when a predetermined iteration termination condition is met, a filter (hereinafter referred to as an inverse filter) to said whitened signal and outputs the results thereof as said restored signal, and applies, when said iteration termination condition is not met, said inverse filter to said whitened signal and outputs the results thereof as an ad-hoc signal; a prediction error filter calculation step wherein a prediction error filter calculation means segments said ad-hoc signal into frames, and outputs a prediction error filter of each of said frames obtained by performing linear prediction analysis on said ad-hoc signal of each frame; an inverse filter calculation step wherein an inverse filter calculation means calculates said inverse filter such that the samples of a concatenation of innovation estimates of said respective frames (hereinafter referred to as an innovation estimate sequence) become mutually independent, where said innovation estimate of a single frame (hereinafter referred to as an innovation estimate) is the signal obtained by applying said prediction error filter of the corresponding frame to the ad-hoc signal of the corresponding frame, and outputs the inverse filter; and a control step wherein a control means iteratively executes said inverse filter application steps, said prediction error filter calculation steps and said inverse filter calculation steps until said iteration termination condition is met. ### Claim at position 11 11-13. (canceled) ### Claim 14 (depends on 1, 2, 3, 4) A computer-readable recording medium having recorded thereon a computer program to function a computer as a signal distortion elimination method according to any of claims 1 to 4. ### Claim 15 (depends on 5) The signal distortion elimination apparatus according to claim 5, wherein: said observed signal is a speech signal including signal distortion.