# US 10,311,891 B2 · Post-processing gains for signal enhancement > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,311,891 B2 - Document ID: US10311891B2 - Status: Granted - Kind: B2 - Application number: 15/433,437 - Filed: 2017-02-15 - Published: 2017-06-08 - Granted: 2019-06-04 - Earliest claimed: 2012-03-23 - Assignees: Dolby Laboratories Licensing Corporation - Applicants: Dolby Laboratories Licensing Corporation - Inventors: Xuejing Sun; Glenn N. Dickins - Web page: https://patentgrep.com/patent/US10311891B2 ## CPC - G10L 21/0364: for improving intelligibility - G10K 11/16: Methods or devices for protecting against, or for damping, noise or other acoustic waves in general (G10K11/36 takes precedence) - G10L 21/0224: Processing in the time domain - G10L 21/0316: by changing the amplitude - G10L 21/034: Automatic adjustment - G10L 25/78: Detection of presence or absence of voice signals (switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10) - H03G 3/301: {the gain being continuously variable} - H03G 3/32: the control being dependent upon ambient noise level or sound level - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING - G10K: SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR - H03G: CONTROL OF AMPLIFICATION ## Abstract A method, an apparatus, and logic to post-process raw gains determined by input processing to generate post-processed gains, comprising using one or both of delta gain smoothing and decision-directed gain smoothing. The delta gain smoothing comprises applying a smoothing filter to the raw gain with a smoothing factor that depends on the gain delta: the absolute value of the difference between the raw gain for the current frame and the post-processed gain for a previous frame. The decision-directed gain smoothing comprises converting the raw gain to a signal-to-noise ratio, applying a smoothing filter with a smoothing factor to the signal-to-noise ratio to calculate a smoothed signal-to-noise ratio, and converting the smoothed signal-to-noise ratio to determine the second smoothed gain, with smoothing factor possibly dependent on the gain delta. ## Claims ### Claim 1 An audio processing apparatus, comprising: at least one processor; and at least one memory storing a computer program; in which the at least one memory with the computer program is configured with the at least one processor to cause the audio processing apparatus to at least: receive at least one input audio signal, determine raw gains to carry out dynamic range control (DRC), and modify the DRC gains and apply them to the input audio signal to remove audible artifacts from the audio output signal, wherein post-processing is applied to the DRC gains to carry out smoothing of the modified DRC gains, wherein the smoothing uses a smoothing factor that is configured to smooth a particular modified DRC gain according to a smoothing time duration that is determined based on a difference in levels of the particular modified DRC gain and a previously smoothed modified DRC gain. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein a first order linear smoothing filter is employed as a post processor. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein a delta smoothing post processor is employed. ### Claim 4 (depends on 3) The apparatus of claim 3, wherein the smoothing is controlled according to an output of a voice activity detector (VAD). ### Claim 5 (depends on 1) The apparatus of claim 1 wherein the post-processing is applied when there is a predefined gain change direction. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein the smoothed DRC gains are combined with the raw DRC gains and evaluated to determine whether the smoothing is too aggressive. ### Claim 7 (depends on 6) The apparatus of claim 6, wherein the determination of whether the smoothing is too aggressive is based on at least one of: perceptual evaluation of speech quality, speech distortion, or signal-to-noise ratio improvement. ### Claim 8 (depends on 3) The apparatus of claim 3, wherein decision-directed gain smoothing is applied to convert the raw DRC gains to signal-to-noise ratios (SNRs), apply a smoothing filter to the SNRs whose smoothing level is controlled by a smoothing factor to calculate smooth SNRs, and convert the smoothed SNRs to smoothed DRC gains. ### Claim 9 (depends on 3) The apparatus of claim 3, wherein smoothing is disabled in the presence of large DRC gains or large gain deltas. ### Claim 10 (depends on 4) The apparatus of claim 4, wherein decision-directed gain smoothing is combined with delta gain smoothing to create a hybrid gain smoother. ### Claim 11 The apparatus of clam 10, wherein at least one of delta gain smoothing or decision-directed gain smoothing is applied to the modified DRC gains based upon a signal classification technique. ### Claim 12 (depends on 1) The apparatus of claim 1, wherein a frame of the input audio signal is transformed into a transform domain. ### Claim 13 A program storage device readable by a machine, tangibly embodying a program of instructions executable by one or more processors of the machine for causing to perform operations, said operations comprising: receiving at least one input audio signal, determining raw gains to carryout dynamic range control (DRC), and modifying the DRC gains and apply them to the input audio signal to remove audible artifacts from the audio output signal, wherein post-processing is applied to the DRC gains to carry out smoothing of the modified DRC gains, wherein the smoothing uses a smoothing factor that is configured to smooth a particular modified DRC gain according to a smoothing time duration that is determined based on a difference in levels of the particular modified DRC gain and a previously smoothed modified DRC gain.