# US 8,571,856 B2 · Limitation of distortion introduced by a post-processing step during digital signal decoding > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,571,856 B2 - Document ID: US8571856B2 - Status: Granted - Kind: B2 - Application number: 12/667,908 - Filed: 2008-07-04 - Published: 2010-09-23 - Granted: 2013-10-29 - Earliest claimed: 2007-07-06 - Assignees: France Telecom - Applicants: Balazs Kovesi; Stéphane Ragot - Inventors: Balazs Kovesi; Stéphane Ragot - Web page: https://patentgrep.com/patent/US8571856B2 ## CPC - G10L 19/26: Pre-filtering or post-filtering - G10L 21/02: Speech enhancement, e.g. noise reduction or echo cancellation (reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08) - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING ## Abstract The invention relates to the processing of a digital signal originating from a decoder and a noise reduction post-processing step, including, in particular, limitation of distortion introduced by the post-processing step in order to deliver a corrected output signal (SOUT), assigning said corrected output signal (SOUT) with: a current amplitude having an intermediary value between a current amplitude value of the post-processed signal (SPOST) and a corresponding current amplitude value of the decoded signal (S′MIC), or the current amplitude of the post-processed signal (SPOST), according to the respective values of the current amplitude of the post-processed signal (SPOST) and by the corresponding current amplitude of the decoded signal (S′MIC). ## Claims ### Claim 1 A method for processing a digital signal, which has been decoded and to which noise reduction post-processing has been applied, to deliver a corrected output signal with reduced distortion introduced by the post-processing, said method comprising the steps of: assigning to the digital signal a current amplitude having an intermediate value between a current amplitude value of the post-processed signal and a corresponding current amplitude value of the decoded signal, or the current amplitude value of the post-processed signal, according to the respective values of the current amplitude of the decoded signal and the current amplitude of the post-processed signal, defining an interval of permitted amplitudes, the interval comprising a lower bound and an upper bound which are dependent on a current amplitude value of the decoded signal, and for a corresponding current amplitude of the post-processed signal, assigning a current amplitude value to the output signal, equal to the value of: the lower bound if the current amplitude of the post-processed signal is below the value of the lower bound, the upper bound if the current amplitude of the post-processed signal is above the value of the upper bound, and the current amplitude of the post-processed signal if the value of the current amplitude of the post-processed signal is included in said interval. ### Claim 2 (depends on 1) The method as claimed in claim 1, wherein a span of amplitude values is assigned to each possible amplitude value of the decoded signal, and the lower and upper bounds are chosen so that the difference between the upper bound and the lower bound is equal to said span of values. ### Claim 3 (depends on 2) The method as claimed in claim 2, wherein the signal received has been coded by a scalar quantization coding, the decoder delivering quantized amplitude values, which vary from one to another in a discrete manner, the successive deviations between the quantized values defining quantization stepsizes, and wherein: the upper bound is given by the addition of substantially half the quantization stepsize to the quantized value assigned to the current amplitude of the decoded signal, and the lower bound is given by the subtraction of substantially half the quantization stepsize from the quantized value assigned to the current amplitude of the decoded signal. ### Claim 4 (depends on 3) The method as claimed in claim 3, wherein the signal received has been coded by a pulse code modulation coding delivering a coded index and wherein respective current values of the lower and upper bounds are determined based on a current coded index, received at the decoder. ### Claim 5 (depends on 4) The method as claimed in claim 4, wherein a correspondence table is provided to give, for a current index received, a corresponding quantized value and a half of a corresponding quantization stepsize, which are determined based on the respective current values of the lower and upper bounds. ### Claim 6 (depends on 1) The method as claimed in claim 1, wherein a delay line is provided so as to ensure a temporal correspondence between said current amplitude of the post-processed signal and said corresponding current amplitude of the decoded signal. ### Claim 7 (depends on 1) The method as claimed in claim 1, implemented for decoded and post-processed signals whose amplitude is above a predetermined threshold value. ### Claim 8 (depends on 1) A non-transitory computer readable medium comprising a computer program comprising instructions for implementing the method as claimed in claim 1. ### Claim 9 A digital signal processing module for processing a digital signal, the signal being decoded and undergoing a noise reduction post-processing, said module limiting a distortion introduced by the post-processing and comprising: a hardware processor that assigns to the digital signal a current amplitude having an intermediate value between a current amplitude value of the post-processed signal and a corresponding current amplitude value of the decoded signal, or the current amplitude value of the post-processed signal, according to the respective values of the current amplitude of the decoded signal and the current amplitude of the post-processed signal, the hardware processor defines an interval of permitted amplitudes, the interval comprising a lower bound and an upper bound which are dependent on a current amplitude value of the decoded signal, and the hardware processor, for a corresponding current amplitude of the post-processed signal, assigns a current amplitude value to the output signal, equal to the value of: the lower bound if the current amplitude of the post-processed signal is below the value of the lower bound, the upper bound if the current amplitude of the post-processed signal is above the value of the upper bound, and the current amplitude of the post-processed signal if the value of the current amplitude of the post-processed signal is included in said interval. ### Claim 10 (depends on 9) A noise reduction post-processing module comprising the digital signal processing module according to claim 9.