# US 9,521,502 B2 · Method for determining a stereo signal > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,521,502 B2 - Document ID: US9521502B2 - Status: Granted - Kind: B2 - Application number: 14/764,754 - Filed: 2013-01-04 - Published: 2016-08-11 - Granted: 2016-12-13 - Earliest claimed: 2013-01-04 - Assignees: Huawei Technologies Co., Ltd. - Applicants: Christof Faller; David Virette; Yue Lang - Inventors: Christof Faller; David Virette; Yue Lang - Web page: https://patentgrep.com/patent/US9521502B2 ## CPC - H04S 7/301: {Automatic calibration of stereophonic sound system, e.g. with test microphone} - H04R 1/406: {microphones} - H04R 3/005: {for combining the signals of two or more microphones (specially adapted for hearing aids H04R25/407)} - H04R 5/027: Spatial or constructional arrangements of microphones, e.g. in dummy heads - H04R 5/04: Circuit arrangements, {e.g. for selective connection of amplifier inputs/outputs to loudspeakers, for loudspeaker detection, or for adaptation of settings to personal preferences or hearing impairments (combinations of amplifiers H03F3/68; stereophonic systems H04S)} - H04S 1/002: {Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution (control circuits for electronic adaptation of the sound field H04S7/30)} - H04S 2400/09: Electronic reduction of distortion of stereophonic sound systems - H04S 2400/15: Aspects of sound capture and related signal processing for recording or reproduction - H04S: STEREOPHONIC SYSTEMS - 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 A method for determining an output stereo signal comprising determining a first differential signal and determining a second differential signal; determining a first power spectrum based on the first differential signal and determining a second power spectrum based on the second differential signal; determining a first weighting function and a second weighting function as a function of the first power spectrum and the second power spectrum; and filtering a first signal, which represents a first combination of the first input audio channel signal and the second input audio channel signal, and filtering a second signal, which represents a second combination of the first input audio channel signal and the second input audio channel signal. ## Claims ### Claim 1 A method for determining an output stereo signal based on an input stereo signal, the input stereo signal comprising a first input audio channel signal and a second input audio channel signal, the method comprising: determining a first differential signal based on a difference of the first input audio channel signal and a filtered version of the second input audio channel signal, and determining a second differential signal based on a difference of the second input audio channel signal and a filtered version of the first input audio channel signal; determining a first power spectrum based on the first differential signal and determining a second power spectrum based on the second differential signal; determining a first weighting function and a second weighting function as a function of the first power spectrum and the second power spectrum, wherein the first weighting function and the second weighting function comprise an exponential function; and filtering a first signal, which represents a first combination of the first input audio channel signal and the second input audio channel signal, with the first weighting function to obtain a first output audio channel signal of the output stereo signal, and filtering a second signal, which represents a second combination of the first input audio channel signal and the second input audio channel signal, with the second weighting function to obtain a second output audio channel signal of the output stereo signal, wherein an exponent of the exponential function lies between 0.5 and 2. ### Claim 2 (depends on 1) The method of claim 1, wherein the first signal is the first input audio channel signal and the second signal is the second input audio channel signal. ### Claim 3 (depends on 1) The method of claim 1, wherein the first signal is the first differential signal and the second signal is the second differential signal. ### Claim 4 (depends on 1) The method of claim 1, further comprising determining a spatial cue, in particular one of a channel level difference, an inter-channel time difference, an inter-channel phase difference and an inter-channel coherence/cross correlation based on the first output audio channel signal and the second output audio channel signal of the output stereo signal. ### Claim 5 (depends on 1) The method of claim 1, wherein the filtered version of the first input audio channel signal is a delayed version of the first input audio channel signal, and wherein the filtered version of the second input audio channel signal is a delayed version of the second input audio channel signal. ### Claim 6 (depends on 1) The method of claim 1, wherein the first input audio channel signal is a first microphone signal of a first microphone, and the second input audio channel signal is a second microphone signal of a second microphone. ### Claim 7 (depends on 1) The method of claim 1, wherein the first and the second microphones are omni-directional microphones. ### Claim 8 A method for determining an output stereo signal based on an input stereo signal, the input stereo signal comprising a first input audio channel signal and a second input audio channel signal, the method comprising: determining a first differential signal based on a difference of the first input audio channel signal and a filtered version of the second input audio channel signal, and determining a second differential signal based on a difference of the second input audio channel signal and a filtered version of the first input audio channel signal; determining a first power spectrum based on the first differential signal and determining a second power spectrum based on the second differential signal; determining a first weighting function and a second weighting function as a function of the first power spectrum and the second power spectrum, wherein the first weighting function and the second weighting function comprise an exponential function; and filtering a first signal, which represents a first combination of the first input audio channel signal and the second input audio channel signal, with the first weighting function to obtain a first output audio channel signal of the output stereo signal, and filtering a second signal, which represents a second combination of the first input audio channel signal and the second input audio channel signal, with the second weighting function to obtain a second output audio channel signal of the output stereo signal, wherein determining the first and the second weighting function comprises: normalizing an exponential version of the first power spectrum by a normalizing function; and normalizing an exponential version of the second power spectrum by the normalizing function, wherein the normalizing function is based on a sum of the exponential version of the first power spectrum and the exponential version of the second power spectrum. ### Claim 9 A method for determining an output stereo signal based on an input stereo signal, the input stereo signal comprising a first input audio channel signal and a second input audio channel signal, the method comprising: determining a first differential signal based on a difference of the first input audio channel signal and a filtered version of the second input audio channel signal, and determining a second differential signal based on a difference of the second input audio channel signal and a filtered version of the first input audio channel signal; determining a first power spectrum based on the first differential signal and determining a second power spectrum based on the second differential signal; determining a first weighting function and a second weighting function as a function of the first power spectrum and the second power spectrum, wherein the first weighting function and the second weighting function comprise an exponential function; and filtering a first signal, which represents a first combination of the first input audio channel signal and the second input audio channel signal, with the first weighting function to obtain a first output audio channel signal of the output stereo signal, and filtering a second signal, which represents a second combination of the first input audio channel signal and the second input audio channel signal, with the second weighting function to obtain a second output audio channel signal of the output stereo signal, wherein the first and the second weighting functions depend on a power spectrum of a diffuse sound of the first input audio channel signal and the second input audio channel signal, in particular a reverberation sound of the first input audio channel signal and the second input audio channel. ### Claim 10 A method for determining an output stereo signal based on an input stereo signal, the input stereo signal comprising a first input audio channel signal and a second input audio channel signal, the method comprising: determining a first differential signal based on a difference of the first input audio channel signal and a filtered version of the second input audio channel signal, and determining a second differential signal based on a difference of the second input audio channel signal and a filtered version of the first input audio channel signal; determining a first power spectrum based on the first differential signal and determining a second power spectrum based on the second differential signal; determining a first weighting function and a second weighting function as a function of the first power spectrum and the second power spectrum, wherein the first weighting function and the second weighting function comprise an exponential function; and filtering a first signal, which represents a first combination of the first input audio channel signal and the second input audio channel signal, with the first weighting function to obtain a first output audio channel signal of the output stereo signal, and filtering a second signal, which represents a second combination of the first input audio channel signal and the second input audio channel signal, with the second weighting function to obtain a second output audio channel signal of the output stereo signal, wherein the first and the second weighting functions depend on a normalized cross correlation between the first and the second differential signals. ### Claim 11 A method for determining an output stereo signal based on an input stereo signal, the input stereo signal comprising a first input audio channel signal and a second input audio channel signal, the method comprising: determining a first differential signal based on a difference of the first input audio channel signal and a filtered version of the second input audio channel signal, and determining a second differential signal based on a difference of the second input audio channel signal and a filtered version of the first input audio channel signal; determining a first power spectrum based on the first differential signal and determining a second power spectrum based on the second differential signal; determining a first weighting function and a second weighting function as a function of the first power spectrum and the second power spectrum, wherein the first weighting function and the second weighting function comprise an exponential function; and filtering a first signal, which represents a first combination of the first input audio channel signal and the second input audio channel signal, with the first weighting function to obtain a first output audio channel signal of the output stereo signal, and filtering a second signal, which represents a second combination of the first input audio channel signal and the second input audio channel signal, with the second weighting function to obtain a second output audio channel signal of the output stereo signal, wherein the first and the second weighting functions depend on a minimum of the first and the second power spectra. ### Claim 12 A method for determining an output stereo signal based on an input stereo signal, the input stereo signal comprising a first input audio channel signal and a second input audio channel signal, the method comprising: determining a first differential signal based on a difference of the first input audio channel signal and a filtered version of the second input audio channel signal, and determining a second differential signal based on a difference of the second input audio channel signal and a filtered version of the first input audio channel signal; determining a first power spectrum based on the first differential signal and determining a second power spectrum based on the second differential signal; determining a first weighting function and a second weighting function as a function of the first power spectrum and the second power spectrum, wherein the first weighting function and the second weighting function comprise an exponential function; and filtering a first signal, which represents a first combination of the first input audio channel signal and the second input audio channel signal, with the first weighting function to obtain a first output audio channel signal of the output stereo signal, and filtering a second signal, which represents a second combination of the first input audio channel signal and the second input audio channel signal, with the second weighting function to obtain a second output audio channel signal of the output stereo signal, wherein determining the first and the second weighting function comprises: W 1 ⁡ ( k , i ) = P 1 β ⁡ ( k , i ) P 1 β ⁡ ( k , i ) + P 2 β ⁡ ( k , i ) and W 2 ⁡ ( k , i ) = P 2 β ⁡ ( k , i ) P 1 β ⁡ ( k , i ) + P 2 β ⁡ ( k , i ) , or comprises: W 1 ⁡ ( k , i ) = P 1 β ⁡ ( k , i ) + ( g - 1 ) ⁢ D β ⁡ ( k , i ) P 1 β ⁡ ( k , i ) + P 2 β ⁡ ( k , i ) and W 2 ⁡ ( k , i ) = P 2 β ⁡ ( k , i ) + ( g - 1 ) ⁢ D β ⁡ ( k , i ) P 1 β ⁡ ( k , i ) + P 2 β ⁡ ( k , i ) , where P1(k,i) denotes the first power spectrum, P2(k,i) denotes the second power spectrum, W1(k,i) denotes the weighting function with respect to the first power spectrum, W2(k,i) denotes the weighting function with respect to the second power spectrum, D(k,i) is a power spectrum of a diffuse sound determined as D(k,i)=Φ(k,i)min (P1(k,i),P2(k,i)), where Φ(k,i) is a normalized cross-correlation between the first and the second differential signals, g is a gain factor, β is an exponent of the exponential function, k is a time index and i is a frequency index. ### Claim 13 An apparatus for determining an output stereo signal based on an input stereo signal, the input stereo signal comprising a first input audio channel signal and a second input audio channel signal, the apparatus comprising a processor for generating the output stereo signal from the first input audio channel signal and the second input audio channel signal by applying a method, wherein the method is for determining an output stereo signal based on an input stereo signal, wherein the input stereo signal comprises a first input audio channel signal and a second input audio channel signal, and wherein the method comprises: determining a first differential signal based on a difference of the first input audio channel signal and a filtered version of the second input audio channel signal, and determining a second differential signal based on a difference of the second input audio channel signal and a filtered version of the first input audio channel signal; determining a first power spectrum based on the first differential signal and determining a second power spectrum based on the second differential signal; determining a first weighting function and a second weighting function as a function of the first power spectrum and the second power spectrum, wherein the first weighting function and the second weighting function comprise an exponential function; and filtering a first signal, which represents a first combination of the first input audio channel signal and the second input audio channel signal, with the first weighting function to obtain a first output audio channel signal of the output stereo signal, and filtering a second signal, which represents a second combination of the first input audio channel signal and the second input audio channel signal, with the second weighting function to obtain a second output audio channel signal of the output stereo signal, wherein the apparatus comprises: a memory for storing a width control parameter controlling a width of the stereo signal, the width control parameter being used by the first weighting function for weighting the first power spectrum and by the second weighting function for weighting the second power spectrum; and/or a user interface for providing the width control parameter. ### Claim 14 An apparatus for determining an output stereo signal based on an input stereo signal, the input stereo signal comprising a first input audio channel signal and a second input audio channel signal, the apparatus comprising a processor for generating the output stereo signal from the first input audio channel signal and the second input audio channel signal by applying a method, wherein the method is for determining an output stereo signal based on an input stereo signal, wherein the input stereo signal comprises a first input audio channel signal and a second input audio channel signal, and wherein the method comprises: determining a first differential signal based on a difference of the first input audio channel signal and a filtered version of the second input audio channel signal, and determining a second differential signal based on a difference of the second input audio channel signal and a filtered version of the first input audio channel signal; determining a first power spectrum based on the first differential signal and determining a second power spectrum based on the second differential signal; determining a first weighting function and a second weighting function as a function of the first power spectrum and the second power spectrum, wherein the first weighting function and the second weighting function comprise an exponential function; and filtering a first signal, which represents a first combination of the first input audio channel signal and the second input audio channel signal, with the first weighting function to obtain a first output audio channel signal of the output stereo signal, and filtering a second signal, which represents a second combination of the first input audio channel signal and the second input audio channel signal, with the second weighting function to obtain a second output audio channel signal of the output stereo signal, wherein the width control parameter is an exponent applied to the first and the second power spectra, the exponent lying in a range between 0.5 and 2. ### Claim 15 (depends on 14) The apparatus of claim 14, wherein the apparatus is a mobile device comprising a first microphone and a second microphone, and wherein the first input audio channel signal is a first microphone signal of the first microphone, and the second input audio channel signal is a second microphone signal of the second microphone.