WO2018073489A1

WO2018073489A1 - Detecting the presence of wind noise

Info

Publication number: WO2018073489A1
Application number: PCT/FI2017/050692
Authority: WO
Inventors: Koray Ozcan; Miikka Vilermo
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2016-10-21
Filing date: 2017-10-03
Publication date: 2018-04-26
Anticipated expiration: 2019-04-21
Also published as: GB2555139A; US10667049B2; EP3530002A4; KR20190067237A; CN109845289B; US20190253795A1; CN109845289A; KR102155976B1; EP3530002A1; GB201617854D0

Abstract

A method comprising: receiving a first microphone signal from a first microphone having a first frequency response characteristic (110₁, 112₁) at frequencies (114) associated with wind noise; receiving a second microphone signal from a second microphone having a second frequency response characteristic (110₂, 112₂) at frequencies (114) associated with wind noise, wherein the first frequency response characteristic (110₁, 112₁) provides less gain than the second frequency response characteristic (110₂, 112₂) over the range of frequencies (114) associated with wind noise; and processing the first microphone signal and the second microphone signal to detect the presence of wind noise.

Description

TITLE

Detecting the presence of wind noise.

TECHNOLOGICAL FIELD

Embodiments of the present invention relate to detecting the presence of wind noise.

BACKGROUND

Wind noise arises from an airflow at or near a microphone which causes pressure variations detected as sound waves. In some examples, the wind may be a naturally generated wind that varies randomly. In other examples, the wind may be a constant air flow that varies relative to a microphone as the environment of the microphone changes, for example, as a device housing the microphone is rotated or moved.

Wind noise can wholly or partially obscure target audio which is desired to be captured by a microphone.

It is therefore desirable to identify when wind noise may be present so that it might be prevented or suppressed. BRIEF SUMMARY

According to various, but not necessarily all, embodiments of the invention there is provided a method comprising: receiving a first microphone signal from a first microphone having a first frequency response characteristic at frequencies associated with wind noise; receiving a second microphone signal from a second microphone having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response characteristic provides less gain than the second frequency response characteristic over the range of frequencies associated with wind noise; and processing the first microphone signal and the second microphone signal to detect the presence of wind noise.

According to various, but not necessarily all, embodiments of the invention there is provided examples as claimed in the appended claims.

BRIEF DESCRIPTION For a better understanding of various examples that are useful for understanding the detailed description, reference will now be made by way of example only to the accompanying drawings in which:

Fig 1 illustrates an example of a method for detecting the presence of wind noise; Fig 2 illustrates an example of frequency response characteristics for the microphones of the apparatus;

Fig 3 illustrates an example of an apparatus;

Fig 4 illustrates an example of an electronic device.

Fig 5 illustrates an example of the apparatus where the processing circuitry is provided by a controller.

Fig 6 illustrates an example of a media capture system that captures images using multiple cameras with different points of view and captures spatial audio using

microphones.

DETAILED DESCRIPTION

Figures, and in particular Fig 1 , illustrate an example of a method 100 for detecting the presence of wind noise. Wind noise arises from an air flow at or near a microphone which causes pressure variations detected as sound waves. In some examples, the wind may be a naturally generated wind that varies randomly. In other examples, the wind may be a constant air flow that varies relative to a microphone as the environment of the

microphone changes, for example, as a device housing the microphone is rotated or moved.

At block 102, the method 100 comprises receiving a first microphone signal 202i from a first microphone 200i having a first frequency response characteristic 1 10i at frequencies 1 14 associated with wind noise. At block 104, the method 100 comprises receiving a second microphone signal 2022 from a second microphone 2ΟΟ2 having a second frequency response characteristic 1 102 at frequencies 1 14 associated with wind noise, wherein the first frequency response characteristic 1 10i provides less gain than the second frequency response characteristic H O2 over the range of frequencies 1 14 associated with wind noise. At block 106, the method 100 comprises processing the first microphone signal 202i and the second microphone signal 2022 to detect the presence of wind noise. The method 100 may, in some examples, comprise additional blocks and sub-blocks not illustrated.

Fig 2 illustrates example frequency response characteristics 1 12 for the microphones 200 of an apparatus 10. A frequency response characteristic is a measure of frequency dependent gain of a microphone. The gain is plotted as the 'y-axis' and frequency plotted as the 'x-axis'.

A frequency response characteristic 1 12i for first microphone 200i and a second frequency response characteristic 1 122 for second microphone 2ΟΟ2 are plotted in this example. The frequencies 1 14 associated with wind noise are illustrated in the figure. The frequencies 1 14 associated with wind noise are in this example, but not necessarily all examples, lower frequencies. These lower frequencies 1 14 may, for example, be less than 200 Hz or less than 100Hz. In other examples, the frequencies 1 14 associated with wind noise are additionally or alternatively mid-range frequencies.

The frequencies 1 14 associated with wind noise may vary with the severity of the wind noise and may, for example, depend upon relative wind speed.

The frequencies 1 14 associated with wind noise may be controlled via mechanical design of the microphone and the microphone environment. The frequencies 1 14 associated with wind noise may therefore be tuned to a be a predetermined one or more frequencies which may, or may not be at lower frequencies.

A first frequency response characteristic 1 10i at frequencies 1 14 associated with wind noise is labelled. This is that portion of the frequency response characteristic 1 12i for the first microphone 200i over the range of frequencies 1 14 associated with wind noise.

A second frequency response characteristic 1 102 at frequencies 1 14 associated with wind noise is labelled. This is that portion of the frequency response characteristic 1 122 for the second microphone 2ΟΟ2 over the range of frequencies 1 14 associated with wind noise.

The first frequency response characteristic 1 10i provides less gain than the second frequency response characteristic 1 122 over the range of frequencies 1 14 associated with wind noise. The difference in gain between the first frequency response characteristic 1 10i and the second frequency response characteristic 1 122 over the range of

frequencies 1 14 associated with wind noise, is labled as gain difference 1 16 in the figure.

The gain difference may be defined as the second frequency response characteristic 1 122 minus the first frequency response characteristic 1 10i over the range of frequencies 1 14. It may, for example be the minimum difference or an average difference such as the mean difference. The different attenuation (gain difference 1 18) arising from the difference between the first frequency response characteristic 1 10i and the second frequency response characteristic 1 102 at frequencies 1 14 associated with wind noise is in this example greater than 6dB. The higher frequencies 1 18 associated with human speech are illustrated in Fig 2. These higher frequencies 1 18 may, for example, be between 400Hz-4kHz.

The frequency response 1 10 of the first microphone 200i compared to the second microphone 2ΟΟ2 is significantly less at frequencies 1 14 associated with wind noise than at higher frequencies 1 18 associated with speech. In the example illustrated in Fig 2, but not necessarily all examples, the difference between the frequency response 1 10 of the first microphone 200i compared to the second microphone 2ΟΟ2 is much greater at the lower frequencies 1 14 associated with wind noise than at higher frequencies 1 18 associated with speech. In the illustrated example, the frequency response 1 10 of the first microphone 200i remains within a range of relatively low gain across the lower frequencies 1 14 and the higher frequencies 1 18 whereas the frequency response 1 10 of the second microphone 2ΟΟ2 is higher across the lower frequencies 1 14 and falls to a lower value, more similar to that of the frequency response 1 10 of the first microphone 200i before the higher frequencies 1 18. The difference in gain between the frequency response 1 10i of the first microphone 200i and the frequency response 1 102 of the second microphone 2ΟΟ2 is therefore large at the lower frequencies 1 14 and much smaller at the higher frequencies 1 18.

In other examples, the profiles of the frequency response 1 10 of the first microphone 200i and the second microphone 2ΟΟ2 may be different. For example, a difference in gain between the frequency response 1 10i of the first microphone 200i and the frequency response 1 1 O2 of the second microphone 2ΟΟ2 may extend to different frequencies 1 14 and into and possibly beyond the higher frequencies 1 18.

The method 100 may be performed by any suitable apparatus 10. One example of an apparatus 10 is described with respect to Fig 3. The apparatus 10 described comprises a plurality of microphones 200 including at least a first microphone 200i and a second microphone 2ΟΟ2. A microphone 200 is any suitable audio transducing means that transduces an incident audio signal to an electrical signal.

The first microphone 200i has a first frequency response characteristic 110i at frequencies 1 14 associated with wind noise and produces a first microphone signal 202i. The second microphone 2002 has a second frequency response characteristic H O2 at frequencies 1 14 associated with wind noise and produces a second microphone signal 202₂.

The first frequency response characteristic 110i provides less gain than the second frequency response characteristic 11 O2 over the range of frequencies 1 14 associated with wind noise, for example as illustrated in Fig 2.

The apparatus 10 described also comprises processing circuitry 220 configured to at least process the first microphone signal 202i and the second microphone signal 2022.

The processing circuitry 220 may be configured to perform the method 100. The processing circuitry may be any suitable processing means.

The apparatus 10 therefore comprises: a first microphone 200i having a first frequency response characteristic 110i at frequencies 1 14 associated with wind noise; a second microphone 2ΟΟ2 having a second frequency response characteristic 1102 at frequencies 1 14 associated with wind noise, wherein the first frequency response characteristic 110i provides less gain than the second frequency response characteristic 1102 over the range of frequencies 1 14 associated with wind noise; and processing circuitry 220 configured to process a first microphone signal 202-i from the first microphone 200i and a second microphone signal 2022from the second microphone 2002to detect the presence of wind noise. In this example the first microphone 200i is wind-suppressed to provide a desired first frequency response characteristic 110i at the frequencies 1 14 associated with wind noise.

In this example the second microphone 2002 has less wind-suppression, for example is not wind-suppressed, to provide a desired second frequency response characteristic 11 O2 at the frequencies 1 14 associated with wind noise.

A difference in mechanical design between the first microphone 200i and the second microphone 2ΟΟ2 causes the differences between the first frequency response characteristic 1 10i and the second frequency response characteristic 1 102 at the frequencies 1 14 associated with wind noise. The mechanical design deliberately introduces a differential response to wind noise. For example, the mechanical design may introduce a frequency-dependent attenuator 210 that reduces the frequency response of the first microphone 200i at frequencies 1 14 associated with wind noise.

In this example, the first microphone 200i comprises a low frequency attenuator 210 that reduces the frequency response of the first microphone 200i at lower frequencies 1 14 associated with wind noise. In this example, the second microphone 2002 does not comprise a low frequency attenuator 210. Where multiple microphones 200 are used only the first microphone 200i would, in this example, comprise a low frequency attenuator 210 and the other microphones 200 would not.

Examples of suitable attenuators include but are not limited to a microphone cover with apertures, a foam rubber cover, a windscreen, or artificial fur.

The method 100 is performed by processing circuitry 220 at blocks 221 -226. The processing circuitry 220 processes the first microphone signal 202i and the second microphone signal 2022 to detect the presence of wind noise.

The block 106 of the method 100, in this example, comprises comparing the first microphone signal 202i and the second microphone signal 2022 only at frequencies 1 14 associated with wind noise, to detect the presence of wind noise. At block 221 , the first microphone signal 202i is pass filtered and the second microphone signal 2022 -pass filtered before being compared to detect the presence of wind noise.

The term 'pass filtering' refers to frequency selective filtering. The filter passes certain frequencies and rejects (attenuates) other frequencies. A pass band filter is one type of pass filter than passes frequencies within a certain band (range) and rejects frequencies outside that range. A low pass filter is one type of pass filter that passes frequencies with a frequency lower than a cut-off frequency. The pass filtering may be performed using a low-pass filter in some examples. The pass filtering may be performed using a band-pass filter in some examples.

One or more pass filters 320 may be used. The pass filter 320 may be a fixed -pass filter that has constant characteristics or may be a variable -pass filter than has variable characteristics such as a variable cutoff frequency and/or frequency response. The-pass filtering may be performed in the analogue domain or the digital domain. Next at blocks 223-224 the processing circuitry 220 processes the (limited frequency) first microphone signal 202i and the (limited frequency) second microphone signal 2022 to detect the presence of wind noise. The (limited frequency) first microphone signal 202i and the (limited frequency) second microphone signal 2022 are compared to detect the presence of wind noise.

At block 223, the processing circuitry 220 compares the (limited frequency) first microphone signal 202i and the (limited frequency) second microphone signal 2022 to detect the presence of wind noise by comparing the (limited frequency) first microphone signal 202i against the (limited frequency) second microphone signal 2022 to detect the presence of wind noise. However, there are a large number of other methods for comparing two different microphone signals.

In this example, if wind noise is detected the method 100 moves to block 226 in the method performed by processing circuitry 220 and if wind noise is not detected the method 100 moves to block 224 in the method performed by processing circuitry 220. That is blocks 223, 224 are sequential. However, in other examples they may be parallel or in reverse sequential order.

At block 224, which is optional, the processing circuitry 220 compares the (limited frequency) first microphone signal 202i and the (limited frequency) second microphone signal 2022 to detect the presence of wind noise by comparing the (limited frequency) first microphone signal 202i against a reference and the (limited frequency) second microphone signal 2022 against a reference to detect the presence of wind noise. This approach can be used to detect when both the (limited frequency) first microphone signal 202i and the (limited frequency) second microphone signal 2022 are clipped because of very high wind noise. In this example, if wind noise is detected , the method 100 moves to block 226 in the method performed by the processing circuitry 220 and if wind noise is not detected the method 100 moves to block 225 in the method performed by the processing circuitry 220.

Where a comparison is performed using the (limited frequency) first microphone signal 202i and the (limited frequency) second microphone signal 2022 for example in block 223, 224, the comparison may use an instantaneous or average amplitude value or may use an instantaneous or average amplitude squared value. The average amplitude squared value represents energy. The comparisons may, for example, comprise comparing energy of the (limited frequency) first microphone signal 202i and energy of the (limited frequency) second microphone signal 2022 to detect the presence of wind noise. The average may be performed over a limited number N of cycles (N>1 ), for example, an average over 4 cycles at 100Hz is equivalent to an average over 0.04 seconds (40ms).

Where the comparison at block 223 comprises comparing energy of the (limited frequency) first microphone signal 202i against the energy of the (limited frequency) second microphone signal 2022 to detect the presence of wind noise, the presence of wind noise may be detected where the energy of the (limited frequency) second microphone signal 2022 exceeds the (limited frequency) first microphone signal 202i by more than a threshold value, for example 6dB.

In some but not necessarily all examples, conditioning of the (limited frequency) first microphone signal 202i and the (limited frequency) second microphone signal 2022 may occur before comparison at blocks 223, 224. In some circumstances it may be desirable to perform a relative normalization (equalization) between the (limited frequency) first microphone signal 202i and the (limited frequency) second microphone signal 2022 before comparison. This may for example comprises adjusting the (limited frequency) first microphone signal 202i and/or the (limited frequency) second microphone signal 2022 in dependence upon a comparison between the first microphone signal 202i and the second microphone signal 2022 at a higher range of frequencies not associated with wind noise e.g. adjusted (limited frequency) first microphone signal 202i (limited frequency) first microphone signal 202i ^* ((higher frequency) second microphone signal 2022 (higher frequency) first microphone signal 202i..

In some but not necessarily all examples, the microphones 200 may have the same directional response. For example, the first microphone 200i and the second microphone 2002 may have the same directionality. In the example illustrated in Fig 4 the first microphone 200i comprises a cover 240 that operates as an attenuator 210. In this example the microphones 200 (the first microphone 200i and the second microphone 2ΟΟ2 ) are integrated within an electronic device 250. An end portion 251 of the electronic device 250 is illustrated in Fig 4. The end portion 251 comprises a cover 240 that forms a low frequency attenuator 210 for the first microphone

As illustrated in the zoomed-in portion of the cover 240 to the right of Fig 4, the cover 240 comprises multiple apertures 212 (through holes) that provide, in combination, an audio pathway to the first microphone 200i inside the device 240 from outside the device 240. In this example the multiple apertures 212 are arranged to be invisible to a human eye in normal viewing conditions (distance e.g. >0.1 m and illumination e.g. <1000lux). For the multiple apertures 212 to be invisible at 10cm to normal adult human with visual acuity 1 MAR, the diameter of each aperture 212 may be smaller than 30 μηη or 50 μηη. In this example, the first microphone200i has a tuned first frequency response

characteristic 1 10i at the band of frequencies 1 14 associated with wind noise by controlling one or more of: the diameter of each aperture 212, the pitch p_x, p_y between apertures 212, depth of each aperture 212, number of apertures 212, and area of coverage of apertures 212. The apertures 212 may comprise a hydrophobic or oleophobic surface treatment of the surface of the cover 240 within and/or adjacent the apertures 212. The surface of the cover defining the apertures 212 may additionally or alternatively be treated to increase surface roughness.

A micro-aperture is an aperture of diameter (maximum dimension) less than 100 μηη. In some examples, the apertures or micro-apertures 212 may have the following modifiable parameters:

diameter, which is the diameter (maximum dimension) of each single aperture 212 (assumed constant from one end of the aperture 212 to the other, for simplicity);

pitch px, which is the distance between the centers of two apertures 212 adjacent in a first direction and/or pitch p_y, which is the distance between the centers of two aperture 212 adjacent in a second direction orthogonal to the first direction;

thickness, which is the thickness of the aperture 212, which in the case of straight aperture 212 is also equivalent to the actual length of each hole;

length, which is the path length of the aperture 212, which in the case of straight aperture 212 is also equivalent to the thickness of each hole;

distribution area, which is the size of the area of the cover 240 that is perforated with apertures 212;

pitch/diameter ratio, which is the ratio of pitch to diameter, and is always greater than 1 ; total open area, which is the combined area of all aperture 212;

relative open area, which is the ratio of total open area to distribution area.

These parameters are selected to achieve a first frequency response characteristic 1 10i that provides less gain than a second frequency response characteristic 1 1 O2 over the range of frequencies 1 14 associated with wind noise. There may be additional design freedom. For example, visibility of apertures 212 may be reduced by reducing the diameter and having a larger pitch/diameter ratio. For example, for good dust protection, a very small diameter (e.g. 0.05 mm or less) may be used with a reasonably small total open area. For example, for good acoustical performance (i.e. a low enough acoustic impedance), a reasonably large diameter (e.g. 0.2 mm) may be used, with large relative open area, and large enough total open area and small thickness (e.g. 0.5 mm). For example, for avoiding the apertures 212 getting fully clogged by grease, a large porous area, large relative open area, and small thickness may be used. For example, for mechanical strength, a large pitch/diameter ratio and large thickness may be used. For example, for good water protection, a small diameter may be used, with a reasonably small total open area.

Referring back to Figs 1 and 3, the method 100 may be extended to include operations that occur after detecting 226 (or not detecting 225) the presence of wind noise.

For example, an output microphone signal may be produced which may be wind-noise suppressed after detecting 226 wind noise and not wind-noise suppressed after not detecting 225 the presence of wind noise. This means that the loss of signal quality arising from wind-noise suppression is selectively applied only when it has an advantage. As an example, if processing the first microphone signal 202i and the second microphone signal 2022 detects the presence of wind noise then the method 100 may comprise, for example at block 226, suppressing wind noise on the first microphone signal 202i and/or second microphone signal 2022 to produce a wind-noise suppressed microphone signal. If processing the first microphone signal 202i and the second microphone signal 2022 does not detect the presence of wind noise then the method 100 may comprise, for example at block 226, not suppressing wind noise on the first microphone signal 202i or second microphone signal 2022 to produce an un-suppressed microphone signal from the first microphone signal 202i and/or second microphone signal 2022.

Wind-noise suppression may for example be achieved by digital processing using a wind suppression algorithm or other processing. As an example, high pass filtering a microphone signal may be used to suppress wind noise. The high-pass filtering may for example use a cut-off frequency at a frequency greater than 100Hz or 200Hz. The high- pass filtering may for example use a cut-off frequency at a frequency less than 400Hz. A decision may be taken as to which of the microphone signals will be selected for production of an output signal.

The production of a wind-noise suppressed microphone signal may comprise selecting the first microphone signal 202i and/or the second microphone signal 2022 for suppression of wind noise. The wind-noise suppressed microphone signal may, for example, comprise exclusively the first microphone signal 202i. The wind-noise suppressed microphone signal may, for example, exclude only the first microphone signal 202i.

The production of a wind-noise suppressed microphone signal may comprise selecting the first microphone signal 202i and the second microphone signal 2022 for wind noise suppression when a first threshold criterion is not satisfied, and selecting the first microphone signal 202i not the second microphone signal 2022 for use with or without wind noise suppression when a first threshold criterion is satisfied. Thus only the first microphone signal 202i may be selected for wind noise suppression when a first threshold criterion is satisfied. A decision may be taken as to if and how the microphone signals will be processed for production of an output signal.

The production of a wind-noise suppressed microphone signal may comprise determining whether or not to apply wind suppression to the first microphone signal 202i.

The production of a wind-noise suppressed microphone signal may comprise selecting the first microphone signal 202i not the first microphone signal 202i for wind noise

suppression when a second threshold criterion is satisfied, and selecting the first microphone signal 202i not the second microphone signal 2022 for use without wind noise suppression when the second threshold criterion is not satisfied.

The first criterion threshold may be a lower threshold for strength of wind noise and the second criterion threshold may be a higher threshold for strength of wind noise.

The following scenarios are therefore possible for example:

Use only audio from the first microphone 202i or microphones 200 with better wind noise suppression

Use only audio from the first microphone 202i or microphones 200 with better wind noise suppression and enable wind noise suppression algorithm from the audio from those microphones 200. Use audio from all microphones 200, but enable wind noise suppression algorithm for the second microphone 2022 or microphones 200 with less or no wind noise suppression

Use audio from all microphones 200, but enable wind noise suppression algorithm for all microphones 200. Use audio from all microphones 200, but enable wind noise suppression algorithm for all microphones 200 using a stronger wind noise suppression algorithm for the second microphone 2022 and other microphones 200 with less or no wind noise suppression

The following scenario is therefore possible for example:

When there is low wind noise (e.g. gain difference 1 16 < 6dB) then use audio from all microphones 200, but enable a wind noise suppression algorithm for all microphones 200.

When there is medium wind noise (e.g. 6dB < gain difference 1 16 < 9dB) use only audio from the first microphone 202i or microphones 200 with better wind noise suppression

When there is high wind noise (e.g. gain difference 1 16≥ 9dB) then use only audio from the first microphone 202i or microphones 200 with better wind noise suppression and enable a wind noise suppression algorithm for the audio from those microphones.

Referring back to Figs 1 and 3, the method 100 may be extended to include operations that occur after detecting 226 (or not detecting) 225 the presence of wind noise.

For example, an output control signal may be produced after detecting wind noise. This may be provided to one or more audio algorithms that require a certain number of microphones and/or a certain microphone at a certain location so that their operation can be adapted.

For example, if processing the first microphone signal 202i and the second microphone signal 2022 detects the presence of wind noise then the method 100, for example at block 226, provides a control output to one or more audio algorithms that require a certain number of microphones and/or a certain microphone at a certain location so that the operation of the algorithm can be adjusted.

The following scenario is therefore possible for example:

If there is only one microphone available (e.g. because it is not disturbed by wind noise) the processing circuitry 220 may only record or may only enable recording in mono. If there are only two microphones available (e.g. because they are not disturbed by wind noise), the processing circuitry 220 may only record or may only enable recording in stereo and only if the two microphones have suitable spatial diversity i.e. one is located to the left of the device250 and one to the right 250 from a device center axis. If there are only three microphones available (e.g. because they are not disturbed by wind noise), the processing circuitry 220 may only record or may only enable recording in spatial audio and only if the microphones have suitable spatial diversity.

If beamforming (reception diversity with phase offset) is used to focus captured sound for example to the direction of a speaker then the selected beamforming algorithm is adjusted according to the number and locations of microphones available (e.g. because they are not disturbed by wind noise).

If it is desired to select a closest microphone, it may only be selected from the

microphones available ((e.g. because they are not disturbed by wind noise). The selected microphone may change with wind conditions. The closest microphone may be known by its location in the device 250 e.g. in a mobile phone the microphone that is closest to the end of the device where users typically has their mouth when speaking. Alternatively, the closest microphone may be selected by choosing the microphone that has largest signal (or best signal to noise ratio) at speech frequencies (400Hz-4kHz).

Spatial audio signals may be captured using microphone arrays. The spatial order depends on the number of microphones available ((e.g. because they are not disturbed by wind noise). A spatial audio system could switch to using a lower order if some of the microphones are or become not available because of wind noise. An example of spatial audio is Ambisonics which is a full-sphere surround sound technique.

Fig 5 illustrates an example of the apparatus 10, where the processing circuitry 220 is provided by a controller.

Implementation of a controller 220 may be as controller circuitry. The controller 220 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). As illustrated in Fig 5 the controller 220 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 234 in a general-purpose or special-purpose processor 230 that may be stored on a computer readable storage medium (disk, memory etc) to be executed by such a processor 230.

The processor 230 is configured to read from and write to the memory 232. The processor 230 may also comprise an output interface via which data and/or commands are output by the processor 230 and an input interface via which data and/or commands are input to the processor 230.

The memory 232 stores a computer program 234 comprising computer program instructions (computer program code) that controls the operation of the apparatus 10 when loaded into the processor 230. The computer program instructions, of the computer program 234, provide the logic and routines that enables the apparatus to perform the methods illustrated in Figs 1 and 3 or discussed herein. The processor 230 by reading the memory 232 is able to load and execute the computer program 234.

The controller 220 therefore comprises:

at least one processor 230; and

at least one memory 232 including computer program code

the at least one memory 232 and the computer program code configured to, with the at least one processor 230, cause the apparatus 10 at least to perform:

processing a first microphone signal received from a first microphone having a first frequency response characteristic at frequencies associated with wind noise and a second microphone signal received from a second microphone having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response provides less gain than the second frequency response over the range of frequencies associated with wind noise, to detect the presence of wind noise.

The computer program 234 may arrive at the apparatus 10 via any suitable delivery mechanism 236. The delivery mechanism 236 may be, for example, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a compact disc read-only memory (CD-ROM) or digital versatile disc (DVD), an article of manufacture that tangibly embodies the computer program 234. The delivery mechanism 236 may be a signal configured to reliably transfer the computer program 234. The apparatus 10 may propagate or transmit the computer program 234 as a computer data signal. Although the memory 232 is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable and/or may provide permanent/semi-permanent/ dynamic/cached storage.

Although the processor 230 is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable. The processor 230 may be a single core or multi-core processor. Fig 6 illustrates an example of a media capture system 402 that captures images using multiple cameras 400 with different points of view and captures audio using microphones 200.

In this example, the fields of view of the cameras 400 overlap to create a large combined field of view for the system. The (still or video) images captured by the cameras 400 may be stitched together to create a panoramic image with a wide field of view. In the example illustrated, the combined field of view of 360° in a horizontal plane. In some examples it may also have simultaneously a large field of view in the vertical plane. A vertical field of view of 180° combined with a horizontal field of view of 360° provides for image capture of the whole of the space surrounding the system 402. It is also desirable to capture not only the visual scene using the cameras 400 but to also simultaneously capture the audio scene using microphones 200. The microphones 200 may be arranged to enable spatial audio, in which a recorded sound source can be rendered at a particular position to a user. This may be used to render a spatial audio sound scene that corresponds to a portion of the panoramic image displayed to a user. This may be particularly useful in mediated reality systems and particularly virtual reality systems where it is desirable to provide a realistic immersive experience. The user may for example control the perspective within the mediated reality by changing their head orientation or gaze direction. The change in head orientation or gaze direction changes the point of view which changes the displayed portion of the panoramic image. It is desirable to have a corresponding change in spatial audio so that the sound scene rotates with the change in user point of view.

In the example of Fig 6, each camera has an associated one or more microphones 200. However, in other implementations at least some of the microphones 200 may alternatively or additionally be moving microphones such as up-close (Lavalier

microphones) or boom microphones, for example.

Any one (or more) of the microphones 200 described in relation to Fig 6 may operate as the first microphone 200i. Any one (or more) of the other microphones 200 described in relation to Fig 6 may operate as the second microphone 2ΟΟ2.

The apparatus 10, including electronic device 250 may be an apparatus or device that comprises multiple microphones 200, such as multimedia capture device: mobile phone, computer tablet, camera, Virtual Reality (VR) camera

References to 'computer-readable storage medium', 'computer program product', 'tangibly embodied computer program' etc. or a 'controller', 'computer', 'processor', 'processing circuitry' , 'processor means' etc. should be understood to encompass not only computers having different architectures such as single /multi- processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field- programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc.

As used in this application, the term 'circuitry' refers to all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) to combinations of circuits and software (and/or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and

(c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

This definition of 'circuitry' applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or other network device.

The blocks illustrated in the figures may represent steps in a method and/or sections of code in the computer program 234. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

Where elements are illustrated in the figures as interconnected this means that they are operationally coupled, and any number or combination of intervening elements can exist (including no intervening elements).

Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described. The apparatus 10 comprises: first audio transducer means having a first frequency response characteristic at frequencies associated with wind noise; second audio transducer means having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response provides less gain than the second frequency response over the range of frequencies associated with wind noise; and processing means for processing a first microphone signal from the first microphone and a second microphone signal from the second microphone to detect the presence of wind noise.

As used here 'module' refers to a unit or apparatus that excludes certain

parts/components that would be added by an end manufacturer or a user. The processing circuitry 220 may be a module.

3

The term 'comprise' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use 'comprise' with an exclusive meaning then it will be made clear in the context by referring to "comprising only one" or by using "consisting".

In this brief description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term 'example' or 'for example' or 'may' in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus 'example', 'for example' or 'may' refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a features described with reference to one example but not with reference to another example, can where possible be used in that other example but does not necessarily have to be used in that other example.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that

modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1 . A method comprising: receiving a first microphone signal from a first microphone having a first frequency response characteristic at frequencies associated with wind noise; receiving a second microphone signal from a second microphone having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response characteristic provides less gain than the second frequency response characteristic over the range of frequencies associated with wind noise; and processing the first microphone signal and the second microphone signal to detect the presence of wind noise.

2. The method as claimed in claim 1 , wherein comparative attenuation arising from the difference between the first frequency response characteristic and the second frequency response characteristic at frequencies associated with wind noise is greater than 6dB.

3. The method as claimed in claim 1 or 2, wherein differences in mechanical design between the first microphone and the second microphone causes differences between the first frequency response characteristic and the second frequency response characteristic at frequencies associated with wind noise.

4. The method as claimed in any preceding claim wherein the different frequency response characteristic of the first microphone compared to the second microphone is significantly less at frequencies associated with wind noise compared to higher frequencies associated with speech.

5. The method as claimed in any preceding claim wherein the first microphone comprises a low frequency attenuator that reduces frequency response of the first microphone at lower frequencies associated with wind noise.

6. The method as claimed in any preceding claim wherein the first microphone comprises a cover comprising multiple apertures.

7. The method as claimed in claim 6, wherein the multiple apertures each have a diameter less than 50 μηη.

8. The method as claimed in claim 6 or 7 wherein the first microphone has a tuned first frequency response characteristic at frequencies associated with wind noise by controlling one or more of: diameter of each aperture, pitch between apertures, depth of each aperture, number of apertures, and area of coverage of apertures.

9. The method as claimed in claim 6, 7 or 8, wherein the apertures comprise a

hydrophobic or oleophobic surface treatment and/or wherein the cover defining the apertures has a surface that has been treated to increase surface roughness.

10. The method as claimed in any preceding claim wherein processing the first microphone signal and the second microphone signal to detect the presence of wind noise comprises comparing the first microphone signal and the second microphone signal to detect the presence of wind noise.

1 1. The method as claimed in claim 10, wherein comparing the first microphone signal and the second microphone signal to detect the presence of wind noise comprises comparing the first microphone signal against the second microphone signal to detect the presence of wind noise.

12. The method as claimed in claim 10, wherein comparing the first microphone signal and the second microphone signal to detect the presence of wind noise comprises comparing the first microphone signal against a reference and the second microphone signal against a reference to detect the presence of wind noise.

13. The method as claimed in any preceding claim wherein processing the first microphone signal and the second microphone signal to detect the presence of wind noise comprises comparing energy of the first microphone signal and energy of the second microphone signal to detect the presence of wind noise.

14. The method as claimed in any preceding claim wherein processing the first microphone signal and the second microphone signal to detect the presence of wind noise comprises comparing the first microphone signal and the second microphone signal to detect the presence of wind noise, wherein one or both of the first microphone signal and the second microphone signal are normalised before comparison to enable the comparison.

15. The method as claimed in claim 14, wherein normalising a microphone signal comprises adjusting the first microphone signal at the range of frequencies and/or the second microphone signal at the range of frequencies in dependence upon a comparison between the first microphone signal and the second microphone signal at a higher range of frequencies not associated with wind noise.

16. The method as claimed in any preceding claim wherein processing the first microphone signal and the second microphone signal to detect the presence of wind noise comprises comparing the first microphone signal and the second microphone signal only at frequencies associated with wind noise, to detect the presence of wind noise.

17. The method as claimed in claim 16 wherein the first microphone signal is low-pass filtered and the second microphone signal is low-pass filtered before being compared to detect the presence of wind noise.

18. The method as claimed in any preceding claim, wherein the first microphone and the second microphone has the same directional response.

19. The method as claimed in any preceding claim, wherein if processing the first microphone signal and the second microphone signal detects the presence of wind noise then suppressing wind noise on the first microphone signal and/or second microphone signal to produce a wind-noise suppressed microphone signal.

20. The method as claimed in claim 19, comprising high pass filtering a microphone signal to suppress wind noise.

21. The method as claimed in claim 19 or 20 further comprising selecting the first microphone signal and/or the second microphone signal for suppression of wind noise.

22. The method as claimed in claim 21 , comprising selecting the first microphone signal and second microphone signal for wind noise suppression when a first threshold criterion is not satisfied, selecting the first microphone signal not the second microphone signal for wind noise suppression when a first threshold criterion is satisfied.

23. The method as claimed in claim 19, 20, 21 or 22 further comprising selecting whether to apply wind suppression to the first microphone signal.

24. The method as claimed in any of claims 19 to 23, comprising selecting the first microphone signal not the first microphone signal for wind noise suppression when a second threshold criterion is satisfied, selecting the first microphone signal not the second microphone signal for use without wind noise suppression when the second threshold criterion is not satisfied.

25. The method as claimed in claim 22 wherein the first criterion threshold is a lower threshold for strength of wind noise and/or as claimed in claim 24 wherein the second criterion threshold is a higher threshold for strength of wind noise.

26. The method as claimed in any preceding claim, wherein if processing the first microphone signal and the second microphone signal detects the presence of wind noise then providing a control output to one or more audio algorithms that require a certain number of microphones and/or a certain microphone at a certain location.

27. The method as claimed in any preceding claim, wherein the first microphone and the second microphone are microphones of a spatial audio system associated with a wide field of view camera system.

28. The method as claimed in any preceding claim, wherein the first microphone and the second microphone are microphones that are integral to an electronic device.

29. An apparatus comprising: at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform the method according to any one or more of the preceding claims.

30. A computer program that, when run on a computer, causes performance of the method according to any one or more of claims 1 to 28.

31. An apparatus comprising: means for performing any one or more of claims 1 to 28.

32. An apparatus comprising: at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform: processing a first microphone signal received from a first microphone having a first frequency response characteristic at frequencies associated with wind noise and a second microphone signal received from a second microphone having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response characteristic provides less gain than the second frequency response characteristic over the range of frequencies associated with wind noise, to detect the presence of wind noise.

33. A computer program that, when run on a computer, causes performance of processing a first microphone signal received from a first microphone having a first frequency response characteristic at frequencies associated with wind noise and a second microphone signal received from a second microphone having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response characteristic provides less gain than the second frequency response characteristic over the range of frequencies associated with wind noise, to detect the presence of wind noise.

34. An apparatus comprising: a first microphone having a first frequency response characteristic at frequencies associated with wind noise; a second microphone having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response characteristic provides less gain than the second frequency response characteristic over the range of

frequencies associated with wind noise; and processing circuitry configured to process a first microphone signal from the first microphone and a second microphone signal from the second microphone to detect the presence of wind noise.

35. An apparatus comprising: first audio transducer means having a first frequency response characteristic at frequencies associated with wind noise; second audio transducer means having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response

characteristic provides less gain than the second frequency response characteristic over the range of frequencies associated with wind noise; and processing means for processing a first microphone signal from the first microphone and a second microphone signal from the second microphone to detect the presence of wind noise.

36. An apparatus comprising: memory and software configured to, with a processor, cause the apparatus to perform at least the following: process a first microphone signal received from a first microphone having a first frequency response characteristic at frequencies associated with wind noise and a second microphone signal received from a second microphone having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response characteristic provides less gain than the second frequency response characteristic over the range of frequencies associated with wind noise, to detect the presence of wind noise.

37. Processor circuitry configured to perform at least the following: process a first microphone signal received from a first microphone having a first frequency response characteristic at frequencies associated with wind noise and a second microphone signal received from a second microphone having a second frequency response characteristic at frequencies associated with wind noise, wherein the first frequency response characteristic provides less gain than the second frequency response characteristic over the range of frequencies associated with wind noise, to detect the presence of wind noise.

38. The apparatus as claimed in claim 36 or processor circuitry as claimed in claim 37, configured to process the first microphone signal and the second microphone signal to detect the presence of wind noise by comparing the first microphone signal and the second microphone signal to detect the presence of wind noise.

39. The apparatus as claimed in claim 36 or processor circuitry as claimed in claim 37, configured to process the first microphone signal and the second microphone signal to detect the presence of wind noise by comparing the first microphone signal against the second microphone signal to detect the presence of wind noise.

40. The apparatus as claimed in claim 36 or processor circuitry as claimed in claim 37, configured to process the first microphone signal and the second microphone signal to detect the presence of wind noise by comparing the first microphone signal against a reference and the second microphone signal against a reference to detect the presence of wind noise.

41 . The apparatus as claimed in claim 36 or processor circuitry as claimed in claim 37, configured to process the first microphone signal and the second microphone signal to detect the presence of wind noise by comparing energy of the first microphone signal and energy of the second microphone signal to detect the presence of wind noise.

42. The apparatus as claimed in claim 36 or processor circuitry as claimed in claim 37, configured to process the first microphone signal and the second microphone signal to detect the presence of wind noise by comparing the first microphone signal and the second microphone signal to detect the presence of wind noise, wherein one or both of the first microphone signal and the second microphone signal are normalised before comparison to enable the comparison.

43. The apparatus as claimed in claim 42 or processor circuitry as claimed in claim 42, wherein normalising a microphone signal comprises adjusting the first microphone signal at the range of frequencies and/or the second microphone signal at the range of frequencies in dependence upon a comparison between the first microphone signal and the second microphone signal at a higher range of frequencies not associated with wind noise.

44. The apparatus as claimed in claim 36 or processor circuitry as claimed in claim 37, configured to process the first microphone signal and the second microphone signal to detect the presence of wind noise by comparing the first microphone signal and the second microphone signal only at frequencies associated with wind noise, to detect the presence of wind noise.

45. The apparatus as claimed in claim 36 or processor circuitry as claimed in claim 37, configured to perform, if processing the first microphone signal and the second microphone signal detects the presence of wind noise, one or more of: selecting the first microphone signal and/or the second microphone signal for suppression of wind noise; and selecting the first microphone signal and/or the second microphone signal for use.

46. The apparatus as claimed in claim 45 or processor circuitry as claimed in claim 45, wherein selecting a microphone signal for use is based on a lower threshold for strength of wind noise and wherein selecting a microphone signal for suppression of wind noise is based on a higher threshold for strength of wind noise

47. The apparatus as claimed in claim 36 or processor circuitry as claimed in claim 37, configured to provide, if processing the first microphone signal and the second microphone signal detects the presence of wind noise, a control output to one or more audio algorithms that require a certain number of microphones and/or a certain microphone at a certain location.