System and method for binaural noise reduction in a sound processing device

Abstract

In one embodiment, the present invention provides a sound processing device with a binaural input and binaural output, where “binaural input” means at least one microphone mounted in or near each ear of the device user, and “binaural output” means at least one output signal directed to each ear. The device may be comprised of two parts connected by a wired or wireless link. The device comprises: at least one microphone in or near each ear for the transduction of the sound at each ear; a signal-to-noise estimation module to estimate the signal-to-noise ratio present at each ear; a comparison and selection module to compare the signal-to-noise ratios present at the two ears and select the ear with the greater signal-to-noise ratio; a noise reduction control module that uses the spectral and temporal information from the selected ear signal to control two identical noise reduction modules; two identical noise reduction modules that process the signals from the two ears, under the control of the control module; and two output modules that amplify the output signals from the noise reduction modules appropriately for each ear and present the amplified signals as sound or other signals to each ear of the device user. The device may be implemented in dedicated hardware embodiment or by software running on a microprocessor.

Claims

1. A method for controlling a sound processing device having a binaural input comprising at least one microphone mounted in or near each ear of the device user, and having a binaural output comprising at least one output signal directed to each ear, the method comprising: transducing sound at each ear, by the respective at least one microphone in or near the ear, to produce a respective signal comprising a digital representation of the sound at each ear; estimating from the digital representation of the sound at each ear a signal-to-noise ratio present in the digital representation of the sound at each ear; selecting the ear with the greater signal-to-noise ratio; applying noise reduction processing to improve a signal to noise ratio of the digital representation of the sound of each ear using at least one noise reduction parameter which is determined based only on information present in the signal of the selected ear, whereby the at least one noise reduction parameter is used as a basis for controlling the noise reduction processing to operate consistently in each ear; and presenting the processed signals to each ear.

2. A method according to claim 1, further comprising amplifying each signal after the noise reduction processing.

3. The method according to claim 1, wherein selecting the ear with the greater signal-to-noise ratio is subject to smoothing and hysteresis, and wherein the at least one noise reduction parameter is determined continuously.

4. A sound processing device having a binaural input comprising at least one microphone mounted in or near each ear of the device user, and having a binaural output comprising at least one output signal directed to each ear, the device comprising: at least one microphone in or near each ear for the transduction of sound at each ear, to produce a respective signal comprising a digital representation of the sound at each ear; a signal-to-noise estimation module to estimate from the digital representation of the sound at each ear a signal-to-noise ratio present in the digital representation of the sound at each ear; a comparison and selection module to compare the signal-to-noise ratios present at the two ears and to select the ear with the greater signal-to-noise ratio; a noise reduction control module that uses information present in the signal of the selected ear to control two noise reduction modules; two noise reduction modules that process the respective digital representations of the sound of the two ears to improve the signal to noise ratio of the digital representations, using at least one noise reduction parameter which is determined based only on information present in the signal of the selected ear, under the control of the control module, whereby the information present in the signal of the selected ear is used as a basis for controlling the noise reduction processing to operate consistently in each ear; and two output modules that present the signals to each ear of the device user.

5. The sound processing device of claim 4 in which the output modules comprise wide dynamic range compression (WDRC) amplifiers with at least one frequency channel.

6. The sound processing device of claim 5 in which the variable gain in each channel of each WDRC amplifier is controlled according to the amplitude information derived from the selected ear with the greater signal-to-noise ratio.

7. The sound processing device of claim 4 in which the output modules comprise Adaptive Dynamic Range Optimisation (ADRO) amplifiers with at least one frequency channel.

8. The sound processing device of claim 7 in which the variable gain in each channel of each ADRO amplifier is controlled according to the amplitude and percentile information derived from the selected ear with the greater signal-to-noise ratio.

9. The sound processing device of claim 4 in which the noise reduction modules use multichannel expansion or spectral subtraction to reduce the gain applied to frequency bands that are determined to be primarily noise, and to increase the gain in frequency bands that are determined to be primarily signal; the choice between whether a frequency band contains primarily noise or signal being based on the instantaneous amplitude and dynamic range of the sound in that frequency band in the selected ear; and wherein the reduction or increase in gain is applied substantially equally and simultaneously to the signal for both ears.

10. The sound processing device of claim 9 in which the control signals derived from the selected ear signal consist of a single bit to encode whether each channel is primarily signal or noise.

11. The sound processing device of claim 4 in which gains or gain reductions are determined for each frequency channel and are transmitted from the selected ear noise reduction control module or output module to the unselected ear noise reduction control module or output module and applied substantially simultaneously to the signal for each ear.

12. The sound processing device of claim 4 in which the amplitude and dynamic range or signal-to-noise ratio for each frequency band are transmitted from the selected ear noise reduction control module and/or output module to the unselected ear noise reduction control module or output module and applied in both ears substantially simultaneously.

13. The sound processing device of claim 4 in which the changes to the gains in individual frequency channels of the noise reduction processing or in the individual frequency channels of the output modules are made slowly and over a time scale of at least 100 ms.

14. The sound processing device of claim 4 in which the operation of a user actuated control on the device is binaurally linked so that any change initiated by the control is applied to both ears substantially simultaneously in a coordinated manner.

15. The sound processing device of claim 4 in which the sound processing in the signal path of each ear is configured to have minimum delay, and to have substantially equal delay from input to output.

16. The sound processing device of claim 4 in which the wired or wireless communication link between the two devices is disabled when the signal-to-noise-ratio in each ear is greater than a configurable threshold value, and enabled when the signal-to-noise-ratio in either ear is below the configurable threshold.

17. The sound processing device of claim 4 where each ear is fitted with a cochlear implant or a hearing aid.

18. The sound processing device of claim 4 where the signal-to-noise ratio in each ear is estimated using the difference between a high percentile estimate and a low percentile estimate.

19. A computer program product comprising computer program code means stored in a non-transitory computer readable medium to make a computer execute a binaural noise reduction sound processing procedure, the computer program product comprising: computer program means accepting at least one input signal comprising a digital representation of sound from at or near each ear of a listener; computer program means for estimating from the digital representation of sound at each ear a signal-to-noise ratio present in the digital representation of the sound at each ear; computer program means for comparing the signal-to-noise ratios present at the two ears and selecting the ear with the greater signal-to-noise ratio; computer program means for using information from the signal of the selected ear to control two noise reduction processes respectively applied to the digital representations of the sound from the two ears to improve a signal to noise ratio of the digital representation, each noise reduction process using at least one noise reduction parameter which is determined based only on information present in the signal of the selected ear, whereby the information present in the signal of the selected ear is used as a basis for controlling the noise reduction processing to operate consistently in each ear; and computer program means for presenting the signals to each ear of the device user.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a block diagram for one embodiment of the binaural noise reduction sound processor.

(2) FIG. 2 illustrates a preferred method of estimating signal-to-noise ratio.

(3) FIG. 3 illustrates a preferred method of comparing signal-to-noise ratio for the two ears and selecting the ear with the better signal-to-noise ratio.

(4) FIG. 4 illustrates a preferred method of controlling the operation of the noise reduction modules.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) FIG. 1 illustrates an example architecture for a pair of devices with sound signal processing incorporating the invention for binaural noise reduction. One or more input signals for the left ear 101 are passed to the left ear signal-to-noise ratio estimator 103 and the left ear noise reduction module 108. The input signals are usually provided by one or more microphones situated in or close to the left ear. Similarly, one or more input signals for the right ear 102 are passed to the right ear signal-to-noise ratio estimator 104 and the right ear noise reduction module 109. The input signals are usually provided by one or more microphones situated in or close to the right ear. The signal-to-noise ratio estimators 103 and 104 estimate the signal-to-noise ratios in the left ear and right ear signals respectively and pass on the estimated signal-to-noise ratios to the binaural comparison and selection module 105. The binaural comparison and selection module 105 may be located in either the left or right ear device, with communication to the other ear by wired or wireless connections. The binaural comparison and selection module compares the two signal-to-noise ratios and selects the ear with greater signal-to-noise ratio. The choice is based on smoothed signal-to-noise ratio data, and hysteresis is applied to avoid excessive or random changes in the selected ear when the signal-to-noise ratio estimates for the two ears are similar. The selected ear indicator is passed to the binaural noise reduction control modules 106 and 107. The noise reduction modules 108 and 109 continuously monitor one or more frequency bands to determine whether the sound in each frequency band is predominantly signal or noise. The signal-or-noise indicators for each band are passed to the binaural noise reduction control modules 106 and 107 respectively. The noise reduction control module for the selected ear returns a set of signal-or-noise indicators to the noise control module for the unselected ear. If the selected ear is the left ear, then the signal-or-noise indicators for the left ear are returned to both amplifier modules 110 and 111. If the selected ear is the right ear, then the signal-or-noise indicators for the right ear are returned to both amplifier modules 110 and 111. The amplifier modules increase or decrease the gains in each frequency band according to the signal-or-noise indicators returned from the binaural noise reduction control module. The processed signal for the left ear is passed from the noise reduction module 108 to the amplifier 110 and thence to the output 112. Similarly, the processed signal for the right ear is passed from the noise reduction module 109 to the amplifier 111 and thence to the output 113. Optionally, the overall gain for the selected ear may be increased by a small amount and the overall gain for the non-selected ear may be decreased by a small amount. Optionally, the noise reduction module in the unselected ear, and the wireless link (if any) from the noise reduction module in the unselected ear, may be turned off to reduce power consumption in the unselected device.

(6) FIG. 2 illustrates a preferred method of estimating the signal-to-noise-ratio for the left ear signal or right ear signal. The intensity calculation module 202 operates by squaring the amplitude of the input signal 201 and taking the logarithm of the squared input signal to give the intensity in decibels (dB). The intensity value is fed to the high percentile estimator 203 and the low percentile estimator 204. Each percentile estimator maintains a “percentile value” which is updated at regular intervals. The intensity value is compared with the percentile value. If the intensity value is greater than the percentile value, the percentile value is incremented by a small fixed amount, the UP STEP. If the intensity value is less than the percentile value, the percentile value is decremented by a small fixed amount, the DOWN STEP. If the ratio of the UP STEP to the DOWN step is 9:1 then the percentile value will tend towards an intensity value at the upper end of the intensity range that is exceeded 10% of the time (9 smaller DOWN STEPS will be balanced by one larger UP STEP). Similarly, if the ratio of the UP STEP to the DOWN STEP is 3:7 then the percentile value will tend towards an intensity value at the lower end of the range that is exceeded 70% of the time (3 larger DOWN STEPS will be balanced by 7 smaller UP STEPS). Other percentages may be selected for the high and low percentile estimators provided that the ratio of the UP STEP to the DOWN STEP is greater for the high percentile estimator than the low percentile estimator. Assuming that the peaks at the upper end of the intensity range are a measure of the signal level and the valleys at the lower end of the intensity range are a measure of the noise level, then the difference 205 between the high percentile value and the low percentile value provides a measure related to the signal to noise ratio (SNR). The difference value is smoothed by module 206 to reduce random variations in the SNR estimates.

(7) FIG. 3 illustrates a preferred method of comparing signal-to-noise ratio for the two ears and selecting the ear with the better signal-to-noise ratio. The smoothed SNR value for the selected ear 301 is compared with the smoothed SNR value for the unselected ear 302 in the threshold, comparison and hysteresis module 303. If the SNR value for the unselected ear is greater than the SNR value for the selected ear plus a fixed amount, Delta, then the unselected ear becomes the selected ear, otherwise, the selected ear remains unchanged. Delta is a small positive amount (1 dB for example) that introduces some hysteresis into the selection of the ear in order to avoid rapid switching if the SNR is similar in the two ears. If the SNR for both ears is greater than a fixed Threshold value (10 dB for example), then neither ear is selected and the binaural noise reduction is switched off to save power.

(8) FIG. 4 illustrates the operation of the binaural noise reduction control modules. A conventional (monaural) noise reduction scheme typically operates by reducing the gain in each frequency channel as the noise level goes up and/or the signal-to-noise ratio goes down. The binaural noise reduction scheme operates in an analogous manner except that the gain reduction is related to the noise level and/or signal-to-noise ratio in the frequency channels of the selected ear. This is achieved by passing information from the selected ear to the unselected ear. In the selected ear, the noise level 402 and the signal-to-noise-ratio 403 for each frequency channel are used to calculate the gain reduction 407 that is passed to the amplifier. Data 406 is also transmitted to the unselected ear. The information passed 406 may include the noise level 402, the signal-to-noise ratio 403, and the gain 407 values for each frequency channel in the selected ear. The choice of information to be transmitted from the selected ear to the unselected ear is optimally made to minimise the power expended in transmitting the information. In the unselected ear, the incoming data received 404 is used to calculate the gains 407 that are passed to the amplifier.

(9) Many alternative noise reduction algorithms may be adapted for use in the binaural noise reduction scheme the subject of this invention. In one embodiment of the invention, the noise reduction scheme is a multichannel scheme which temporarily reduces the gain applied to frequency channels that are thought to be primarily noise, and increases the gain in frequency channels that are thought to be primarily signal. The choice between whether a frequency channel contains primarily noise or signal is preferably based on instantaneous amplitude 402 and signal-to-noise ratios 403 of the sound in that frequency channel in the selected ear. In a preferred embodiment of this type, the 30.sup.th and 90.sup.th percentiles of the amplitude are calculated in each frequency channel. If the amplitude is below the 30.sup.th percentile, or the 90.sup.th percentile is less than 2 dB above the 30.sup.th percentile, the frequency channel is judged to contain mostly noise, otherwise the frequency channel is judged to contain primarily signal. The reduction in gain for channels that are primarily noise and increase in gain for frequency channels that are mostly signal are applied equally and simultaneously to the signal for both ears. The control signals derived from the selected ear signal can be particularly simple in this case, for example, a 32-channel noise reduction scheme can be controlled by sending 32 bits to encode whether each channel is primarily signal (bit value=1) or noise (bit value=0). Preferably, a maximum cumulative gain reduction and a maximum cumulative gain increase are applied in each frequency channel.

(10) In a second embodiment of the invention, the gains or gain reductions for each frequency channel are calculated in the selected ear in the same manner as for a conventional monaural noise reduction scheme and transmitted from the selected ear to the unselected ear and applied simultaneously to the signal for each ear.

(11) In a third embodiment of the invention, the amplitude and dynamic range (or signal-to-noise ratio) for each frequency band are transmitted from the selected ear to the unselected ear and applied in identical noise reduction algorithms in both ears simultaneously.

(12) The advantages of these embodiments of the present invention comprise: more accurate assessment of signal and noise levels in the unselected ear by utilizing information from the ear with the better SNR; avoidance of the creation of artificial streaming events that could disrupt the normal binaural processing of sounds; emphasize the signal relative to the noise in such a manner as to improve the signal-to-noise ratio in the unselected ear; minimizing the data transmission requirements and hence minimizing the additional power consumption of the devices; intelligently switching data transmission from one ear to the other to halve power consumption relative to a device that always transmits data in both directions; and intelligently switching off data transmission when binaural noise reduction is not required to reduce battery consumption.

(13) Some portions of this detailed description are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent series of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

(14) As such, it will be understood that such acts and operations, which are at times referred to as being computer-executed, include the manipulation by the processing unit of the computer of electrical signals representing data in a structured form. This manipulation transforms the data or maintains it at locations in the memory system of the computer, which reconfigures or otherwise alters the operation of the computer in a manner well understood by those skilled in the art. The data structures where data are maintained are physical locations of the memory that have particular properties defined by the format of the data. However, while the invention is described in the foregoing context, it is not meant to be limiting as those of skill in the art will appreciate that various of the acts and operations described may also be implemented in hardware.

(15) It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the description, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

(16) It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.