Method for integrated microphone measurement

Abstract

An apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the system at least to: obtain at least one audio signal from an integrated microphone based on a measurement audio signal; obtain at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone; determine a first property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal; determine a second property based on the at least one measurement microphone audio signal and the measurement audio signal; and determine the integrated microphone characteristic based on the first property and the second property.

Description

METHOD FOR INTEGRATED MICROPHONE MEASUREMENTFIELD

[0001] The present application relates to a method, apparatus, system and computer program for measuring integrated microphones using a measurement microphone, for example a probe microphone, and in particular but not exclusively to method, apparatus, system and computer program for integrated microphone characteristics, for example frequency responses of integrated microphone, using a measurement microphone.BACKGROUND

[0002] The rapid advancement of Large Language Models (LLMs) is opening a new era of consumer devices, characterized by increasingly sophisticated voice-activated interfaces. This transformative trend is driving a surge in the integration of microphones into a wide range of devices such as Automotive, industrial, mics integrated to structures such as cockpits, dashboards, walls, kitchen appliances, home automation systems, robots, gaming devices and toys.

[0003] Traditional communication devices, such as smartphones, have furthermore been driving investment in the development of robust and high performance MEMS microphone technologies, enabling the integration of microphones into compact mechanics and providing reliable audio capture even in harsh environmental conditions. As such these MEMS microphone technologies are being integrated into the devices such as discusses above.

[0004] The quality of output from the voice-activated interfaces is directly relative to knowledge of the performance of the microphone and the integration of the microphone with respect to the device in question.

[0005] Advancements in manufacturing technologies have reduced manufacturing tolerances. This has enabled consistent performance in mass produced microphones. In practice, the performance of the microphone, for example the frequency response of a device microphone, is typically influenced more by the microphone integration than by the transducer characteristics. The integrated microphone frequency response is a product of the device shape, microphone integration-related mechanics, assembly tolerances, gaskets, and ingress protection features such as membranes or meshes.

[0006] Partly due to industrial design and ingress protection requirements, the microphone integration is intentionally hidden or made quite invisible; a typical microphone inlet is a small 0.8-1.5 mm hole in the device surface.

[0007] Conventional microphone measurement and performance verification typically requires a traditional acoustic laboratory where the measurements are performed in expensive controlled acoustic spaces such as anechoic chambers, where the entire product can be taken into a silent space without room reflections.SUMMARY

[0008] According to a first aspect, there is provided an apparatus for determining an integrated microphone characteristic, the apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the system at least to: obtain at least one audio signal from an integrated microphone based on a measurement audio signal; obtain at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone; determine a first property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal; determine a second property based on the at least one measurement microphone audio signal and the measurement audio signal; and determine the integrated microphone characteristic based on the first property and the second property.

[0009] The integrated microphone property may comprise at least one of: a total harmonic distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an acoustic overloading point of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a signal to noise ratio of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone noise floor of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone spectral distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone signal cross-correlation of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone signal coherence of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a transfer function of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a frequency response of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; and a time domain impulse response of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal.

[0010] The second property may comprise at least one of: a total harmonic distortion of the measurement microphone with respect to the measurement audio signal; an acoustic overloading point of the measurement microphone with respect to the measurement audio signal; a signal to noise ratio of the measurement microphone with respect to the measurement audio signal; an integrated microphone noise floor of the measurement microphone with respect to the measurement audio signal; an integrated microphone spectral distortion of the measurement microphone with respect to the measurement audio signal; an integrated microphone signal cross-correlation of the measurement microphone with respect to the measurement audio signal; an integrated microphone signal coherence of the measurement microphone with respect to the measurement audio signal; a transfer function of the measurement microphone with respect to the measurement audio signal; a frequency response of the measurement microphone with respect to the measurement audio signal; and a time domain impulse response of the measurement microphone with respect to the measurement audio signal.

[0011] The measurement microphone sound-inlet may be located relative to the sound inlet of the integrated microphone with a gap based on a physical size and / or geometry of the measurement microphone soundinlet, the gap preventing the measurement microphone sound-inlet blocking or acoustic shadowing the sound inlet of the integrated microphone.

[0012] The measurement microphone sound-inlet may be positioned such that the sound inlet of the integrated microphone and a center of the measurement microphone sound-inlet are coincident.

[0013] The measurement microphone sound-inlet may be positioned such that the sound inlet of the integrated microphone and the center of the measurement microphone sound-inlet are aligned to an outward surface normal of the sound inlet of the integrated microphone.

[0014] The apparatus may further comprise: the integrated microphone; the measurement microphone; and a support structure configured to support the integrated microphone and the measurement microphone such that the measurement microphone sound-inlet is located substantially close to a sound inlet of the integrated microphone and with axes of the measurement microphone sound-inlet and sound inlet of the integrated microphone substantially aligned.

[0015] The apparatus may further comprise the measurement source.

[0016] The measurement source may comprise a loudspeaker, wherein the axes of the measurement microphone sound-inlet and sound inlet of the integrated microphone are substantially aligned with an output axis of the loudspeaker.

[0017] The apparatus may be further caused to: obtain at least one audio signal from a reference microphone, the at least one audio signal from the reference microphone based on a calibration sound source audio signal; determine a first calibration property based on the at least one audio signal from the reference microphone and the calibration sound source audio signal; obtain at least one further measurementmicrophone audio signal from the measurement microphone based on the calibration sound source audio signal, the measurement microphone sound-inlet configured to be substantially aligned and located relative; determine a second calibration property based on the at least one further measurement microphone audio signal and the calibration sound source audio signal; determine a measurement microphone calibration response based on the first calibration property and the second calibration characteristic, wherein the apparatus caused to determine the integrated microphone characteristic based on the first property and the second property is caused to determine the integrated microphone characteristic based on the measurement microphone calibration response.

[0018] The at least one audio signal from the reference microphone may be based on a transduction of an acoustic wave generated from a calibration sound source.

[0019] The at least one further measurement microphone audio signal may be based on a transduction of an acoustic wave generated from the calibration sound source.

[0020] The measurement microphone calibration property may comprise at least one of: a measurement microphone calibration signal total harmonic distortion; a measurement microphone calibration acoustic overloading point; a measurement microphone calibration signal to noise ratio; a measurement microphone calibration noise floor; a measurement microphone calibration spectral distortion; a measurement microphone calibration signal cross-correlation; a measurement microphone calibration signal coherence; a measurement microphone calibration transfer function; a measurement microphone calibration frequency response; and a measurement microphone calibration time domain impulse response.

[0021] The first calibration property may comprise at least one of: a total harmonic distortion of the reference microphone with respect to the calibration source audio signal; an acoustic overloading point of the reference microphone with respect to the calibration source audio signal; a signal to noise ratio of the reference microphone with respect to the calibration source audio signal; an integrated microphone noise floor of the reference microphone with respect to the calibration source audio signal; an integrated microphone spectral distortion of the reference microphone with respect to the calibration source audio signal; an integrated microphone signal cross-correlation of the reference microphone with respect to the calibration source audio signal; an integrated microphone signal coherence of the of the reference microphone with respect to the calibration source audio signal; a transfer function of the reference microphone with respect to the calibration source audio signal; a frequency response of the reference microphone with respect to the reference source audio signal; and a time domain impulse response of the reference microphone with respect to the measurement audio signal.

[0022] The second calibration property may comprise at least one of: a total harmonic distortion of the measurement microphone with respect to the calibration source audio signal; an acoustic overloading point of the measurement microphone with respect to the calibration source audio signal; a signal to noise ratio ofthe measurement microphone with respect to the calibration source audio signal; an integrated microphone noise floor of the measurement microphone with respect to the calibration source audio signal; an integrated microphone spectral distortion of the measurement microphone with respect to the calibration source audio signal; an integrated microphone signal cross-correlation of the measurement microphone with respect to the calibration source audio signal; an integrated microphone signal coherence of the measurement microphone with respect to the calibration source audio signal; a transfer function of the measurement microphone with respect to the calibration source audio signal; a frequency response of the measurement microphone with respect to the calibration source audio signal; and a time domain impulse response of the measurement microphone with respect to the calibration source audio signal.

[0023] The apparatus may be further caused to at least one of: align the second property based on the at least one measurement microphoneaudio signal and the measurement audio signal with the first property function based on the at least one audio signal from the integrated microphone and the measurement audio signal; align the at least one audio signal from the integrated microphone with the at least one measurement microphone audio signal based on a comparison between the first property based on the at least one audio signal from the integrated microphone and the second property based on the at least one measurement microphoneaudio signal; align the at least one audio signal from the integrated microphone with the at least one measurement microphone audio signal based on a comparison between the first property; the at least one audio signal from the integrated microphone and the at least one measurement microphone audio signal; and align the measurement audio signal, the at least one audio signal from the integrated microphone, and the at least one measurement microphone audio signal based on an obtained synchronization signal, wherein the synchronization signal is obtained from one of: the measurement source; and a synchronization source.

[0024] The synchronization signal may further synchronize the at least one audio signal from the reference microphone and the at least one further measurement microphone audio signal.

[0025] The at least one audio signal from the integrated microphone may be based on a transduction of an acoustic wave generated from the measurement source.

[0026] The at least one measurement microphone audio signal may be based on a transduction of the acoustic wave from the measurement source.

[0027] The measurement microphone may be a probe microphone, wherein the probe microphone comprises one of: a probe-tip located substantially close to the sound inlet of the integrated microphone and with axes of a sound-inlet of the probe-tip and the sound inlet of the integrated microphone substantially aligned; and no probe-tip located substantially close to the sound inlet of the integrated microphone and with axes of a sound-inlet of the probe microphone and the sound inlet of the integrated microphone substantially aligned.

[0028] According to a second aspect, there is provided an apparatus for determining an integrated microphone characteristic, the apparatus comprising means configured to:: obtain at least one audio signal from an integrated microphone based on a measurement audio signal; obtain at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone; determine a first property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal; determine a second property based on the at least one measurement microphone audio signal and the measurement audio signal; and determine the integrated microphone characteristic based on the first property and the second property.

[0029] The integrated microphone property may comprise at least one of: a total harmonic distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an acoustic overloading point of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a signal to noise ratio of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone noise floor of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone spectral distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone signal cross-correlation of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone signal coherence of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a transfer function of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a frequency response of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; and a time domain impulse response of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal.

[0030] The second property may comprise at least one of: a total harmonic distortion of the measurement microphone with respect to the measurement audio signal; an acoustic overloading point of the measurement microphone with respect to the measurement audio signal; a signal to noise ratio of the measurement microphone with respect to the measurement audio signal; an integrated microphone noise floor of the measurement microphone with respect to the measurement audio signal; an integrated microphone spectral distortion of the measurement microphone with respect to the measurement audio signal; an integrated microphone signal cross-correlation of the measurement microphone with respect to the measurement audiosignal; an integrated microphone signal coherence of the measurement microphone with respect to the measurement audio signal; a transfer function of the measurement microphone with respect to the measurement audio signal; a frequency response of the measurement microphone with respect to the measurement audio signal; and a time domain impulse response of the measurement microphone with respect to the measurement audio signal.

[0031] The measurement microphone sound-inlet may be located relative to the sound inlet of the integrated microphone with a gap based on a physical size and / or geometry of the measurement microphone soundinlet, the gap preventing the measurement microphone sound-inlet blocking or acoustic shadowing the sound inlet of the integrated microphone.

[0032] The measurement microphone sound-inlet may be positioned such that the sound inlet of the integrated microphone and a center of the measurement microphone sound-inlet are coincident.

[0033] The measurement microphone sound-inlet may be positioned such that the sound inlet of the integrated microphone and the center of the measurement microphone sound-inlet are aligned to an outward surface normal of the sound inlet of the integrated microphone.

[0034] The apparatus may further comprise: the integrated microphone; the measurement microphone; and a support structure configured to support the integrated microphone and the measurement microphone such that the measurement microphone sound-inlet is located substantially close to a sound inlet of the integrated microphone and with axes of the measurement microphone sound-inlet and sound inlet of the integrated microphone substantially aligned.

[0035] The apparatus may further comprise the measurement source.

[0036] The measurement source may comprise a loudspeaker, wherein the axes of the measurement microphone sound-inlet and sound inlet of the integrated microphone are substantially aligned with an output axis of the loudspeaker.

[0037] The means may be further configured to: obtain at least one audio signal from a reference microphone, the at least one audio signal from the reference microphone based on a calibration sound source audio signal; determine a first calibration property based on the at least one audio signal from the reference microphone and the calibration sound source audio signal; obtain at least one further measurement microphone audio signal from the measurement microphone based on the calibration sound source audio signal, the measurement microphone sound-inlet configured to be substantially aligned and located relative; determine a second calibration property based on the at least one further measurement microphone audio signal and the calibration sound source audio signal; determine a measurement microphone calibration response based on the first calibration property and the second calibration characteristic, wherein the apparatus caused to determine the integrated microphone characteristic based on the first property and thesecond property is caused to determine the integrated microphone characteristic based on the measurement microphone calibration response.

[0038] The at least one audio signal from the reference microphone may be based on a transduction of an acoustic wave generated from a calibration sound source.

[0039] The at least one further measurement microphone audio signal may be based on a transduction of an acoustic wave generated from the calibration sound source.

[0040] The measurement microphone calibration property may comprise at least one of: a measurement microphone calibration signal total harmonic distortion; a measurement microphone calibration acoustic overloading point; a measurement microphone calibration signal to noise ratio; a measurement microphone calibration noise floor; a measurement microphone calibration spectral distortion; a measurement microphone calibration signal cross-correlation; a measurement microphone calibration signal coherence; a measurement microphone calibration transfer function; a measurement microphone calibration frequency response; and a measurement microphone calibration time domain impulse response.

[0041] The first calibration property may comprise at least one of: a total harmonic distortion of the reference microphone with respect to the calibration source audio signal; an acoustic overloading point of the reference microphone with respect to the calibration source audio signal; a signal to noise ratio of the reference microphone with respect to the calibration source audio signal; an integrated microphone noise floor of the reference microphone with respect to the calibration source audio signal; an integrated microphone spectral distortion of the reference microphone with respect to the calibration source audio signal; an integrated microphone signal cross-correlation of the reference microphone with respect to the calibration source audio signal; an integrated microphone signal coherence of the of the reference microphone with respect to the calibration source audio signal; a transfer function of the reference microphone with respect to the calibration source audio signal; a frequency response of the reference microphone with respect to the reference source audio signal; and a time domain impulse response of the reference microphone with respect to the measurement audio signal.

[0042] The second calibration property may comprise at least one of: a total harmonic distortion of the measurement microphone with respect to the calibration source audio signal; an acoustic overloading point of the measurement microphone with respect to the calibration source audio signal; a signal to noise ratio of the measurement microphone with respect to the calibration source audio signal; an integrated microphone noise floor of the measurement microphone with respect to the calibration source audio signal; an integrated microphone spectral distortion of the measurement microphone with respect to the calibration source audio signal; an integrated microphone signal cross-correlation of the measurement microphone with respect to the calibration source audio signal; an integrated microphone signal coherence of the measurement microphone with respect to the calibration source audio signal; a transfer function of the measurementmicrophone with respect to the calibration source audio signal; a frequency response of the measurement microphone with respect to the calibration source audio signal; and a time domain impulse response of the measurement microphone with respect to the calibration source audio signal.

[0043] The means may be further configured to at least one of: align the second property based on the at least one measurement microphoneaudio signal and the measurement audio signal with the first property function based on the at least one audio signal from the integrated microphone and the measurement audio signal; align the at least one audio signal from the integrated microphone with the at least one measurement microphone audio signal based on a comparison between the first property based on the at least one audio signal from the integrated microphone and the second property based on the at least one measurement microphoneaudio signal; align the at least one audio signal from the integrated microphone with the at least one measurement microphone audio signal based on a comparison between the first property; the at least one audio signal from the integrated microphone and the at least one measurement microphone audio signal; and align the measurement audio signal, the at least one audio signal from the integrated microphone, and the at least one measurement microphone audio signal based on an obtained synchronization signal, wherein the synchronization signal is obtained from one of: the measurement source; and a synchronization source.

[0044] The synchronization signal may further synchronize the at least one audio signal from the reference microphone and the at least one further measurement microphone audio signal.

[0045] The at least one audio signal from the integrated microphone may be based on a transduction of an acoustic wave generated from the measurement source.

[0046] The at least one measurement microphone audio signal may be based on a transduction of the acoustic wave from the measurement source.

[0047] The measurement microphone may be a probe microphone, wherein the probe microphone comprises one of: a probe-tip located substantially close to the sound inlet of the integrated microphone and with axes of a sound-inlet of the probe-tip and the sound inlet of the integrated microphone substantially aligned; and no probe-tip located substantially close to the sound inlet of the integrated microphone and with axes of a sound-inlet of the probe microphone and the sound inlet of the integrated microphone substantially aligned.

[0048] According to a third aspect, there is provided a method for an apparatus for determining an integrated microphone characteristic, the method comprising: obtaining at least one audio signal from an integrated microphone based on a measurement audio signal; obtaining at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone; determining a first property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphoneaudio signal; determining a second property based on the at least one measurement microphone audio signal and the measurement audio signal; and determining the integrated microphone characteristic based on the first property and the second property.

[0049] The integrated microphone property may comprise at least one of: a total harmonic distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an acoustic overloading point of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a signal to noise ratio of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone noise floor of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone spectral distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone signal cross-correlation of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone signal coherence of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a transfer function of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a frequency response of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; and a time domain impulse response of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal.

[0050] The second property may comprise at least one of: a total harmonic distortion of the measurement microphone with respect to the measurement audio signal; an acoustic overloading point of the measurement microphone with respect to the measurement audio signal; a signal to noise ratio of the measurement microphone with respect to the measurement audio signal; an integrated microphone noise floor of the measurement microphone with respect to the measurement audio signal; an integrated microphone spectral distortion of the measurement microphone with respect to the measurement audio signal; an integrated microphone signal cross-correlation of the measurement microphone with respect to the measurement audio signal; an integrated microphone signal coherence of the measurement microphone with respect to the measurement audio signal; a transfer function of the measurement microphone with respect to the measurement audio signal; a frequency response of the measurement microphone with respect to the measurement audio signal; and a time domain impulse response of the measurement microphone with respect to the measurement audio signal.

[0051] The measurement microphone sound-inlet may be located relative to the sound inlet of the integrated microphone with a gap based on a physical size and / or geometry of the measurement microphone sound-inlet, the gap preventing the measurement microphone sound-inlet blocking or acoustic shadowing the sound inlet of the integrated microphone.

[0052] The measurement microphone sound-inlet may be positioned such that the sound inlet of the integrated microphone and a center of the measurement microphone sound-inlet are coincident.

[0053] The measurement microphone sound-inlet may be positioned such that the sound inlet of the integrated microphone and the center of the measurement microphone sound-inlet are aligned to an outward surface normal of the sound inlet of the integrated microphone.

[0054] The apparatus may comprise: the integrated microphone; the measurement microphone; and a support structure configured to support the integrated microphone and the measurement microphone such that the measurement microphone sound-inlet is located substantially close to a sound inlet of the integrated microphone and with axes of the measurement microphone sound-inlet and sound inlet of the integrated microphone substantially aligned.

[0055] The apparatus may further comprise the measurement source.

[0056] The measurement source may comprise a loudspeaker, wherein the axes of the measurement microphone sound-inlet and sound inlet of the integrated microphone are substantially aligned with an output axis of the loudspeaker.

[0057] The method may further comprise: obtaining at least one audio signal from a reference microphone, the at least one audio signal from the reference microphone based on a calibration sound source audio signal; determine a first calibration property based on the at least one audio signal from the reference microphone and the calibration sound source audio signal; obtain at least one further measurement microphone audio signal from the measurement microphone based on the calibration sound source audio signal, the measurement microphone sound-inlet configured to be substantially aligned and located relative; determine a second calibration property based on the at least one further measurement microphone audio signal and the calibration sound source audio signal; determine a measurement microphone calibration response based on the first calibration property and the second calibration characteristic, wherein the apparatus caused to determine the integrated microphone characteristic based on the first property and the second property is caused to determine the integrated microphone characteristic based on the measurement microphone calibration response.

[0058] The at least one audio signal from the reference microphone may be based on a transduction of an acoustic wave generated from a calibration sound source.

[0059] The at least one further measurement microphone audio signal may be based on a transduction of an acoustic wave generated from the calibration sound source.

[0060] The measurement microphone calibration property may comprise at least one of: a measurement microphone calibration signal total harmonic distortion; a measurement microphone calibration acousticoverloading point; a measurement microphone calibration signal to noise ratio; a measurement microphone calibration noise floor; a measurement microphone calibration spectral distortion; a measurement microphone calibration signal cross-correlation; a measurement microphone calibration signal coherence; a measurement microphone calibration transfer function; a measurement microphone calibration frequency response; and a measurement microphone calibration time domain impulse response.

[0061] The first calibration property may comprise at least one of: a total harmonic distortion of the reference microphone with respect to the calibration source audio signal; an acoustic overloading point of the reference microphone with respect to the calibration source audio signal; a signal to noise ratio of the reference microphone with respect to the calibration source audio signal; an integrated microphone noise floor of the reference microphone with respect to the calibration source audio signal; an integrated microphone spectral distortion of the reference microphone with respect to the calibration source audio signal; an integrated microphone signal cross-correlation of the reference microphone with respect to the calibration source audio signal; an integrated microphone signal coherence of the of the reference microphone with respect to the calibration source audio signal; a transfer function of the reference microphone with respect to the calibration source audio signal; a frequency response of the reference microphone with respect to the reference source audio signal; and a time domain impulse response of the reference microphone with respect to the measurement audio signal.

[0062] The second calibration property may comprise at least one of: a total harmonic distortion of the measurement microphone with respect to the calibration source audio signal; an acoustic overloading point of the measurement microphone with respect to the calibration source audio signal; a signal to noise ratio of the measurement microphone with respect to the calibration source audio signal; an integrated microphone noise floor of the measurement microphone with respect to the calibration source audio signal; an integrated microphone spectral distortion of the measurement microphone with respect to the calibration source audio signal; an integrated microphone signal cross-correlation of the measurement microphone with respect to the calibration source audio signal; an integrated microphone signal coherence of the measurement microphone with respect to the calibration source audio signal; a transfer function of the measurement microphone with respect to the calibration source audio signal; a frequency response of the measurement microphone with respect to the calibration source audio signal; and a time domain impulse response of the measurement microphone with respect to the calibration source audio signal.

[0063] The method may further comprise: aligning the second property based on the at least one measurement microphone audio signal and the measurement audio signal with the first property function based on the at least one audio signal from the integrated microphone and the measurement audio signal; aligning the at least one audio signal from the integrated microphone with the at least one measurement microphone audio signal based on a comparison between the first property based on the at least one audiosignal from the integrated microphone and the second property based on the at least one measurement microphone audio signal; aligning the at least one audio signal from the integrated microphone with the at least one measurement microphone audio signal based on a comparison between the first property; the at least one audio signal from the integrated microphone and the at least one measurement microphone audio signal; and aligning the measurement audio signal, the at least one audio signal from the integrated microphone, and the at least one measurement microphone audio signal based on an obtained synchronization signal, wherein the synchronization signal is obtained from one of: the measurement source; and a synchronization source.

[0064] The synchronization signal may further synchronize the at least one audio signal from the reference microphone and the at least one further measurement microphone audio signal.

[0065] The at least one audio signal from the integrated microphone may be based on a transduction of an acoustic wave generated from the measurement source.

[0066] The at least one measurement microphone audio signal may be based on a transduction of the acoustic wave from the measurement source.

[0067] The measurement microphone may be a probe microphone, wherein the probe microphone comprises one of: a probe-tip located substantially close to the sound inlet of the integrated microphone and with axes of a sound-inlet of the probe-tip and the sound inlet of the integrated microphone substantially aligned; and no probe-tip located substantially close to the sound inlet of the integrated microphone and with axes of a sound-inlet of the probe microphone and the sound inlet of the integrated microphone substantially.

[0068] According to a fifth aspect, there is an apparatus comprising: obtaining circuitry configured to obtain at least one audio signal from an integrated microphone based on a measurement audio signal; obtaining circuitry configured to obtain at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone; determining circuitry configured to determine a first property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal; determining circuitry configured to determine a second property based on the at least one measurement microphone audio signal and the measurement audio signal; and determining the integrated microphone characteristic based on the first property and the second property.

[0069] According to a sixth aspect, there is an apparatus comprising: means for obtaining at least one audio signal from an integrated microphone based on a measurement audio signal; means for obtaining at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone; means for determining a first propertybased on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal; means for determining a second property based on the at least one measurement microphone audio signal and the measurement audio signal; and determining the integrated microphone characteristic based on the first property and the second property.

[0070] .According to a seventh aspect, there is provided a non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least the method according to any of the preceding aspects.

[0071] According to an eighth aspect there is provided a computer program comprising instructions [or a computer readable medium comprising instructions] for causing an apparatus, caused to perform at least the following: obtaining at least one audio signal from an integrated microphone based on a measurement audio signal; obtaining at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone; determining a first property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal; determining a second property based on the at least one measurement microphone audio signal and the measurement audio signal; and determining the integrated microphone characteristic based on the first property and the second property.

[0072] In the above, many different embodiments have been described. It should be appreciated that further embodiments may be provided by the combination of any two or more of the embodiments described above.DESCRIPTION OF FIGURES

[0073] Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

[0074] Fig.1 shows schematically an example microphone integration apparatus suitable for testing according to some embodiments;

[0075] Fig.2 shows example graphs of probe or measurement microphone calibration employing the modified free-field method according to some embodiments;

[0076] Fig.3 shows schematically an example microphone integration measurement system or apparatus according to some embodiments;

[0077] Fig.4 shows schematically an example probe or measurement microphone apparatus according to some embodiments;

[0078] Fig.5 shows example graphs of a free-field directional response Hfof the example integrated microphone under test for various rotation angles;

[0079] Figs.6a and 6b shows example graphs of pressure frequency response of the integrated microphone under test, with 1 / 36th octave smoothing, measured in both the anechoic chamber and in the control room and the 95% confidence intervals magnitude and phase component for the measurements;

[0080] Figs.7a, 7b, and 7c show graphs of tree-field directional response Hfof the integrated microphone measured based on the application of some embodiments, alongside directly measured responses from the anechoic chamber Hff

[0081] Figs.8a, 8b, 8c, 8d and 8e show schematically apparatus according to some embodiments employing differing synchronization approaches;

[0082] Fig.9 shows a flow diagram of the operations of some embodiments attempting to determine pressure response of the integrated microphone;

[0083] Fig.10 shows a flow diagram of the operations of some embodiments attempting to calibrate the measurement method as described in Fig.9;

[0084] Fig.11 shows apparatus suitable for implementing some embodiments; and

[0085] Fig.12 shows a simulated response of an integrated microphone under test using a % inch microphone and a probe microphone with a tube diameter of 1.2 mm.DETAILED DESCRIPTION

[0086] The concept, as discussed in further detail in the embodiments herein, is related to apparatus and methods to measure integrated microphone properties such as transfer function, frequency response (or others such as pressure frequency responses). The problem as discussed above is that typically measurements are made by a traditional acoustic laboratory comprising expensive controlled acoustic spaces such as anechoic chambers, where the entire product can be taken into a silent space without room reflections.

[0087] The embodiments herein therefore comprise apparatus and measurement methods that enable fully integrated product mechanics for arbitrary devices to be measured without the use of controlled laboratory space.

[0088] This is useful in product design and quality control allowing quicker and cheaper measurements to be made and enabling rapid prototyping and design of integrated microphones in consumer devices. Furthermore these apparatus and method enable the testing of integrated devices which cannot be measured in an anechoic environment. For example, integrated microphones in automotive or vehicle interior, where free-field measurements cannot even be made, and current approaches of acoustic simulation of the entire space produce inaccurate results when compared to the following embodiments.

[0089] The embodiments, as discussed herein, aim to reduce the effect or eliminate variable factors from the measurement environment. These variables are acoustic environment and shape of the physical device surrounding the microphone.

[0090] Possible applications of this measurement approach are product design, verification of product design, product fault detection, quality control, possible microphone characterization in software.

[0091] In the following embodiments a probe microphone is employed to enable a measurement of integrated product microphones. During research this measurement method has been called Integrated Microphone Pressure Frequency Response Measurement using Probe microphone, and abbreviated as IMPro. The IMPro method uses a probe microphone to measure the sound pressure at the sound inlet of the integrated microphone. This information is combined with the microphone transducer output signal to calculate the desired measurement property. In the following examples the desired measurement property is a pressure frequency response of the integrated microphone, but could be any suitable measurement property such as transfer function or frequency response.

[0092] The examples described herein refer to the use of a probe microphone to assist in the measurement of the integrated microphone under test. However, any suitable measurement microphone could be used, provided that the size of the microphone is sufficiently small. In some embodiments, the measurement frequency range sets the limits of what is considered to be sufficiently small for the suitable measurement microphone. For the highest frequency measured, the product of wavenumber (the ratio of angular frequency to the speed of sound in the test medium) and the largest cross-sectional dimension should be less than 1. This ensures that the measurement microphone is almost invisible to the sound waves that are measured by the microphone, and also that of the integrated microphone.

[0093] Fig 12, for example, shows a simulated response of an example integrated microphone under test using a % inch microphone 1201 and a probe microphone 1202 with a tube diameter of 1.2 mm. For the % inch microphone ka=1 occurs at 8.5 kHz, whereas for the probe microphone, ka=1 occurs at 46 kHz. In some embodiments a probe microphone is considered to be any microphone that meets the dimension requirements previously stated.

[0094] In some embodiments other small microphone components can be employed without probe-tip type of structure when the physical size of the microphone is small enough for the measurement frequency band to satisfy the measurement accuracy requirements. Measurement grade probe microphones have reliable electronics and transducers that provide reliable results in repeated measurement for extended periods of time without need for frequent calibration, but if the microphone calibration can be made more frequently even for each measurement series, high quality microphone components that have been designed for consumer products, like hearing aids, may also provide reliable results after careful calibration.

[0095] In the following examples this measurement can be conducted in any suitable location, for example a typical office environment, without the need for an expensive anechoic chamber.

[0096] Additionally, these embodiments permit the microphones to be measured after they have been integrated into the structure of the product. While product development typically prototypes and tests new designs with rapid prototyping techniques, the following embodiments permit the measurement or validation of product design despite the employment of different manufacturing processes with mechanical tolerance differences. In other words, being able to test or validate a design using final product hardware. As such the embodiments described herein is useful in the electro-acoustic optimization of products with integrated microphones and in improving product audio quality.

[0097] In the following example a MEMS microphone is integrated into a simple rigid spherical prototype with known analytical sound scattering properties, but it would be understood that the integration can be with any suitable shape or size or configuration, and also not limited to MEMS microphone types.

[0098] Measurement results in the following have been validated with measurements conducted both in an approximately 5 m x 5 m x 5 m anechoic chamber and in an audio laboratory control room that has acoustics comparable with that of a typical quiet office environment.

[0099] A typical, or idealised, embodiment of an integrated microphone device can be shown schematically with respect to Fig.1. Fig.1 shows the integrated microphone device 100. The device 100 comprises a MEMS microphone capsule 101 which is configured to transduce any received acoustic waves into audio signals.

[0100] The MEMS microphone capsule 101 is located on a circuit board 109 which can receive the audio signals.

[0101] The sound inlet 113 is typically a small opening in the outer shell 115 of the device 101, and is the outer-most extent of the microphone sound port 103. The sound port 103 can consists of a series of holes cutting through the outer shell 115, a gasket sealing material 105 and a printed circuit board 109 as well as the microphone capsule’s own sound port.

[0102] The gasket 105 will typically include a dust and water ingress shield. The illustrated structure pertains to bottom port MEMS microphones, which have their sound port on the PCB contact face, but corresponding acoustic structures can be found for other microphone types such as top port MEMS microphones, piezo microphones, electret microphones, or condenser microphones, which may have different packaging and electrical interfaces.

[0103] Microphones sealing against the outer shell of the device is very common in devices that try to hide the presence of microphones by minimizing the size of the microphone inlet hole for desired industrial design target, Microphone integration can also have some alternative design targets, such as passive wind noise attenuation. In this type of designs, it is quite common to use acoustically transparent protective mesh, perforated surfaces, or some other porous materials, which effectively have multitude of small sound inletsaround limited surface area. This type of microphone integration can also enable structures to include multiple microphones under shared protective mesh surface. When the protective surface is effectively acoustically transparent, the embodiments described herein (the IMPro method) can consider this protective surface as exterior space of the microphone, which means that the reference point 111 is located under the protective cover next to the microphone sound port 103.

[0104] The sound port may have a number of different cross-sectional shapes along its length. It produces a low-pass acoustic filter for the microphone capsule. It is generally recommended that the microphone integration utilizes a simple and short sound port structure, but it is not uncommon that design limitations in product mechanics lead to more complicated structures with acoustic resonances that need to be compensated for with filtering of the microphone signal. A designer can predict these problems and simulate the combined response with either the lumped acoustic component approach or with more complex finite element methods. Determining the characteristics of the different design parameters of the sound port structure may be difficult to model, especially in the case of complex port geometries and ingress screens.

[0105] The number of sound ports that an integrated microphone may have is not limited to a single port. In cases where there are multiple sound ports, measurements can be made on the individual ports, where the remaining sound ports are blocked with a suitable acoustic sound wave blocking material, that either blocks, or terminates the sound port with an appropriate acoustic impedance. Blocking the ports may cause a change in the measurement results, but the information gained may be of benefit.

[0106] To be able to compare the response of the model to a free-field response specification, a means of modelling the external sound field and radiation characteristics is required, and the modelling assumptions may lead to very different outcomes. Comparing simulation results with measurements would be easier if the device’s external shape could be disregarded. The following discussion relate to how probe microphone measurements can be utilized in the context of microphone integration.

[0107] The following discussion describes the determination or estimation of a pressure frequency response of the integrated microphone as the property to be measured. In some embodiments this estimation or determination provides substantially the frequency characterization of the microphone output signal to a known input pressure. This differs from the free-field frequency response, where only the sound pressure at a reference position in the absence of the microphone object is known. The pressure response of the microphone is independent of the external sound field, and so employing this response as target for microphone design would negate the need to simulate the external sound field.

[0108] Typically, the pressure response of a microphone is measured by placing the microphone and a sound source in a small enclosing cavity, which has dimensions which are small compared to the sound wavelength within the measured frequency band. It is assumed that the pressure within the enclosing volume is of a constant known value, or at least accurately predictable at a point within the volume; hence thepressure at the sound port of the microphone is known. However, for larger objects this is not a feasible procedure, or at least is limited to low frequency measurement.

[0109] The pressure response of an integrated microphone can be thought of as the tree-field response with any scattering effects caused by the device removed. The underlying assumption in the following embodiments is that sound pressure at the reference point 111 shown in Fig.1 is equal to the sound pressure entering the microphone sound inlet 113. This assumption is valid if the reference point is substantially the same point (in other words very close «1 mm) as the sound inlet (113). The value kd (where k is the measured wavenumber, and d is the distance between the reference point and the sound port) should be less than 1 for the points to be considered the same.

[0110] The pressure frequency response Hmcan be determined based on the following equation

[0111] where Hi is the measured transfer function of the integrated microphone output signal to a loudspeaker sound source, and pinis the sound pressure at the reference point. The pressure at the reference point is determined by measuring the transfer function Hpof a probe microphone output signal to the same source loudspeaker stimulus, correcting the measured response with the calibrated frequency response of the probe microphone Hprobeas discussed in the following equation.

[0112] Using the equations (1) and (2) the desired pressure response Hmcan be determined simply as

[0113] For the valid assumption that the sound inlet and measurement reference pressures are equal, the probe must be placed as close as possible to the sound inlet (or in other words the probe must be placed substantially at the sound inlet). Ideally, the probe-tip would be touching the surface. However, if the probetip is placed too close to the sound inlet, the physical size of the probe-tip may distort the end correction of the microphone sound port, which would result in a change in its acoustic mass and resistance, and inadvertently modify the resonance characteristics of the integrated microphone.

[0114] For a circular inlet, the probe should not be placed closer than the diameter of the inlet. If the probe tube is oriented such that the sound inlet and probe tube axes are orthogonal, the probe tip will sample pressures over a range of distances plus or minus the internal radius R of the probe tube from the probe tube central axis, which may cause phase smearing at high frequencies, depending on the diameter of the probe, or the measurement frequency range. With the probe tube and sound inlet axes aligned, the probe tubesamples pressure at the same distance from the inlet. If the sound inlet is of similar diameter to the probe tip, the pressure should be constant over the probe tip area, if the value of kR is less than 1.

[0115] Probe microphones in some situations can be supplied with a variety of different probe-tube lengths. With a shorter probe tube, the sensitivity at higher frequencies is improved. However, short tubes bring the probe microphone body closer to the device being measured and increase the strength of any reflections between the microphones. Longer tubes may begin to vibrate due to the loudspeaker stimulus, and this vibration may cause resonances to appear in measured responses that are not characteristic of the integrated microphone. If it is a valid assumption that the sound inlet pressure and the reference point pressures are equal, then it should be possible to successfully measure the integrated microphone pressure response in any room, such as in an office, rather than under anechoic conditions.

[0116] In an office room, there may be problems if either the loudspeaker or the reference point is located at a pressure nodal point, as the pressure level at the reference point may be below the noise floor of either of the two microphones leading potentially to inaccurate measurement results due to low SNR.

[0117] Additionally in some embodiments the probe microphone can also be calibrated in the same environment or a suitable environment, for example an office environment. Probe microphones have frequency responses that are dependent on the attached probe tube, and therefore can be calibrated against a reference microphone. Suppliers of probe tube microphones provide adapters to allow pressure calibration of the probe microphone following standard practices, and require that a measurement microphone be used as a sound source; additional equipment that is required for a very limited purpose. Free-field calibration on the other hand avoids this, but does unfortunately require an anechoic test chamber. A probe microphone calibrated following the free-field simultaneous standardized method such as described in IEC, 61094:8 (2012): Measurement microphones - Part 8: Methods for determining the free-field sensitivity of working standard microphones by comparison, International Electrotechnical Commission, 2012 places the probe tip and the reference microphone close together, and assumes that both microphones measure exactly the same pressure. The pressure measured by the probe-tip should be equal to the average pressure over the area of the reference microphone membrane if the microphone is sufficiently small enough compared to the measured wavelength, which should be the case for a 1 / 4 inch measurement microphone in excess of 20 kHz.

[0118] The calibration process can, for example in some embodiments, be implemented by placing together the reference microphone, of sensitivity Sref(unit / Pa) and the probe microphone Sensitivity is expressed typically using millivolts per Pascal (mV / Pa) for analog microphones and decibels relative to full scale per Pascal (dBFS / Pa) for digital microphones. In this placement the probe-tube tip of the probe microphone is placed about 0.5 mm from the outer surface of the reference microphones protection grid, with the tip at the center point of the reference microphone.

[0119] The transfer function Hrof the reference microphone output to the source loudspeaker stimulus, and Hcfor the probe microphone transfer function for the calibration is measured or otherwise determined from a measured microphone audio signal. The probe microphone calibration frequency response Hprobe, which is used in the equation (3) above can be defined as follows:

[0120] The comparison calibration method assumes that the reference microphone has a known response in a well defined measurement environment. In a normal office room, this is not the case, and so corrections to the reference microphone response to account for the measurement environment mismatch can be applied in some embodiments.

[0121] For example a conventional or normal office room is neither free-field nor diffuse field, but somewhere in-between. For a 1 / 4 inch microphone the deviation from diffuse to free-field or pressure-field responses at 20 kHz is small but not insignificant, and dependent on the incident angle of the arriving sound. Hence, there may be slight differences in the implied response of the reference microphone, depending on the measurement location within the room, and the strength of the different reflections arriving at the reference microphone.

[0122] In some embodiments by spatially averaging the measurement, the reference microphone’s assumed response will tend towards a random incidence response, and the effect of the measurement environment reduced.

[0123] Furthermore corrections for random incidence could then be applied, or a suitable random-incidence measurement microphone used. The data presented in Fig.2 shows that it is possible to calibrate a probe microphone using this modified free-field method, the left side of Fig.2 shows probe microphone calibration frequency responses for magnitude and phase delay in both control room 203 / 223 and anechoic chamber 201 / 221 (and the min / max values 205 / 225). Furthermore, on the right side is shown the statistical variation in the probe microphone calibration frequency response in both magnitude (for anechoic 211 / and control room 213) and phase (for anechoic 231 / and control room 233). The differences in the reference microphone response to the anechoic and office environment sound fields are clearly seen.

[0124] In some embodiments where an anechoic chamber, nor pressure calibration equipment is available, then a probe microphone can be calibrated in a normal office room. This statement is made based on intended use of the calibration data, and the intended application area for the integrated microphone. It is for the user to determine if the accuracy is sufficient for the intended use of the acquired measurement data.

[0125] In conclusion, calibration results illustrated in Fig.2 suggest that both of these calibration methods are feasible for IMPro method and would not limit the use of probe microphone as calibrated referencemicrophone. However, calibration in office environment is expected to be slower due to need for increased averaging of repeated measurement results.

[0126] In order to test the validity of the IMPro methodology, an integrated microphone prototype was constructed and measured, which is shown schematically in Fig.3. In this example the system comprises a digital MEMS microphone 311, housed in a rigid hollow sphere 307, with similar internal structures to that depicted in Fig.1. In the following example the MEMS microphone with a front face sound port was soldered onto a small circuit board. The circuit board was attached and sealed against the inner surface of the spherical shell with a gasket. A hole of 1.0 mm was drilled through the shell cover within the gasket area, thus creating a short, sealed sound port connection to the microphone membrane. This prototype did not include filter materials protecting against dust or water 107. The sphere 307 was of diameter 90.0 mm, and the microphone sound inlet was positioned at the spherical coordinates (r,0,cp) of (45 mm, 0°, 35.5°). A 3 / 8 inch 16 threaded insert, located at (45 mm, 0°, -90°), allowed the sphere microphone to be easily connected to a microphone stand or stereo T-bar (not shown). This insert also set as the rotational axis for the sphere microphone. The MEMS microphone was connected to a custom computer USB interface, which allowed direct capture of the microphone’s digital signal. The equipment required for the IMPro measurement comprises, a reference microphone (not shown), a loudspeaker 301, a probe microphone 303 including probe microphone transducer housing 304, and mechanical hardware to reliably position the probe microphone tip 305 at the required position 309. The probe microphone used in this study was fitted with a 80 mm long probe-tube 306.

[0127] Positioning the tip can be challenging, as small movements of the microphone body result in much larger movements of the tip. In some embodiments there can be employed a dial-gauge positioning arm, used by machinists, allows easy general positioning of the tip, and locks rigidly in place. The arm used also included some fine adjustment of the probe-tip in one axis.

[0128] To help place the probe-tip a measurable distance from a sound inlet surface, displacement adjustment along the length of the probe tube can be implemented, and a simple 3-D printable jig such as shown in Fig 4 can be employed. For example Fig.4 shows the microphone tube 305 being mounted on the microphone (body) 303 which is fixed by tightening a knob 405 and can be positioned accurately by use of a knurled dial or knob 412. In some embodiments the distance between the probe microphone tube-tip and the integrated microphone sound inlet can be assessed by any suitable means, for example by the use of Feelergauges, such as used in automotive repair.

[0129] The integrated microphone being tested (or the reference microphone for probe calibration can furthermore in some embodiments be mounted to a stereo T-bar, to which a positioning arm is also securely mounted using an appropriate thread adapter. The T-bar can then be attached to a microphone stand.

[0130] Fig.3 therefore shows an example of the positioning setup (without showing the mounting structure). This arrangement can allow rigid positioning of the two microphones relative to one another, but allows easyrotation of the microphone assembly about a microphone-stand shaft axis. Placing the loudspeaker and microphone assembly on different microphone stands helps to reduce vibrational coupling.

[0131] Fig.3 furthermore shows the electronic device or apparatus 341 coupled to the loudspeaker 301, the probe microphone 303 and the integrated microphone 311 under test. In this example a nominal position of the integrated microphone assembly 311, the probe tube 306 and loudspeaker 301 radiation axes are aligned. A loudspeaker 301 sound source can for example be placed in some embodiments on a microphone stand at a distance of 50 cm from the microphones. The integrated microphone 311 device under test is securely mounted in a suitable holder, which is in turn attached to a T-bar mounted on a second microphone stand. To the same T-bar, the probe microphone positioning arm is rigidly attached. The microphone assembly stand is adjusted to permit small rotations of the assembly about the microphone stand shaft.

[0132] In some embodiments other means for securing the microphones can be employed.

[0133] In some embodiments, the loudspeaker could be contained within the enclosure containing the integrated microphone under test. With this measurement configuration, more properties describing both the integrated microphone and the integrated loudspeaker may be obtained in addition to interaction properties between the two integrated components.

[0134] The combined measurement setup in some embodiments is positioned in a room away from any walls and strongly reflecting surfaces.

[0135] For the following reported data, the measurements were conducted in an acoustic laboratory control room with hard concrete floor, but otherwise typical office room acoustics. The probe microphone probe-tip can, as described above, be positioned such that the integrated microphone sound inlet and the center of the probe-tip are coincident and aligned to the outward surface normal of the sound inlet. The alignment of the probe tube to the sound inlet surface normal yields more accurate results, but other alignments will achieve very similar data depending on the measurement frequency. The gap between the device sound inlet surface and probe-tip furthermore can be adjusted such that a 1.0 mm thickness feeler-gauge just fits through the gap. The loudspeaker level for the sine sweep is set to be approximately 30 dB above the background noise level. Sine seep measurements are repeated 20 times and the microphone assembly is rotated within the range ±20° in small increments between consecutive measurement.

[0136] In some embodiments, the gap may be different from 1.0 mm. The gap should be measured and stated. It should meet the kd> 1 requirement. The level of the sound source above the background noise level is for guidance. Other levels that provide data may be used. The number measurement repetitions and the range of angles measured is also a guide, other methods to introduce some amount of spatial variation between measurements can be used.

[0137] If the shape of the device surfaces in the region around the sound inlet make the placement of the probe tip at the reference point (111), then the probe should be placed such that the acoustic pressure at the updated reference point (111) is a close as possible to the pressure at the sound inlet (113).

[0138] For the reported data, the logarithmic sine sweep recordings were processed according to the method described in Muller, S. and Massarani, P., “Transfer-function measurements with sweeps— Director’s cut including previously unreleased material and some corrections,” Journal of the Audio Engineering Society. Audio Engineering Society, 49, p. 443-471 , 2001 to obtain the transfer functionsand Hpfor the sphere and probe microphones respectively, and used to determine the pressure response Hmof the sphere microphone.

[0139] In some embodiments, other measurement stimuli can be used, for example, but not limited to Maximum Length Sequence (MLS) signals, sweeped sine, pseudo noise, random noise, or combinations of them.

[0140] In some embodiments the sphere and probe microphone signals are not acquired or captured with the same hardware.

[0141] Time alignment of the impulse responses could therefore in some embodiments by synchronized by quadratic fitting of the sub-sampled impulse to with 1 / 64th of a sample. Alignment was ensured between the two microphone signals, and also between the repeated measurements, thus minimizing issues caused by sample clock rate differences.

[0142] To evaluate the statistical variation of the pressure response measurement Hm, the set of repeated measurements of HtlHpas well as the set of measurement data obtained for the probe microphone response calibration Hprobecan be individually combined to create a set of all possible pressure responses.

[0143] In some embodiments the Log10 magnitude and unwrapped phase forms of the Hmdata set can be processed using the bootstrap bias and accelerated percentile method Efron, B. and Tibshirani, R., An Introduction to the Bootstrap, Chapman & Hall / CRC Monographs on Statistics & Applied Probability, Taylor & Francis, 1994, ISBN 9780412042317 to determine, for each frequency point, the mean response components and their 95% confidence intervals, based on a bootstrap count of 2000.

[0144] Other embodiments may or may not implement other statistical methods to obtain the desired output data from the measurement data collected.

[0145] In some embodiments verification measurements of the IMPro method can be conducted on the sphere microphone under anechoic conditions. The microphone assembly setup was the same as that described above and used in the control room. However, the loudspeaker source distance was 1.21 m, and only 11 repeated measurements were made within a range of ±10° of microphone assembly rotation.

[0146] To verify that the IMPro pressure response measured is correct, a reference measurement was determined, and the tree-field directional response Hffof the sphere microphone was deemed suitable,since equivalent data could be generated from the measured pressure response Hmand analytical model data for the primary and scattered pressure caused by a rigid sphere from a point source radiator as described in Beranek, L. and Mellow, T., Acoustics: Sound Fields and Transducers, chapter 12.4, Elsevier Science, 2012, ISBN 97801.

[0147] For this model, the sound pressure at a point on the horizontal plane (r, a) from a point source of strength Uois determined from the sum of the primary pdand scattered pspressures:

[0148] For the total pressure ptto be equivalent to the freefield measurement data, this pressure should be normalized with the pressure prefthat which is produced by the same point source in the absence of the sphere microphone at the free-field reference position:

[0149] Where k is the wave-number, and d is the distance from the point source to the sphere center; i.e., the reference point. If the point ptis chosen to be the same measurement reference point for which the pressure frequency response Hmis measured, then the product of these two quantities give the signal output of the sphere microphone. Thus the transfer function Hfof the sphere microphone signal to the reference pressure Prefis

[0150] and Hfshould be equivalent to measurements of the directional free-field sphere microphone frequency response Hff. For the sphere microphone, the Hmreference point can be located 1.0 mm from the surface of the sphere microphone, with spherical coordinates (46 mm, 0°, 35.3°). As this point is not located on the horizontal plane, the angle of rotation 0 of the sphere microphone about the vertical axis, and the angle a used in the analytical model are not equivalent. Conversion of the angle 0 to a can be provided byoc(0) = cos-1(coscp COS0) (8)

[0151] where (p=35.3° for the probe reference point. The calculated values of Hffor the 90 mm sphere, at a distance 1.21 m from the point source at various rotation angles 0 are shown in Fig.5.

[0152] In some embodiments, the external pressure at the DUT microphone sound inlet could be determined by other numerical acoustic methods, such as boundary, finite or infinite element methods.

[0153] The following describes measured pressure frequency response (Hm) of the sphere microphone in both anechoic and control room environments obtained using the IMPro method, along with the measuredfree-field directional responses (Hff) and their synthesized versions (Hf) using the analytical scattering model data.

[0154] Fig.6 for example shows a pressure frequency response of the sphere microphone, with 1 / 36th octave smoothing, measured in both the anechoic chamber and in the control room.

[0155] In Fig.6a is shown the mean responses plotted along with the maximum and minimum measured frequency point values. The 95% confidence intervals magnitude and phase component for the measurements are shown in Fig.6b. To determine the pressure response of the sphere microphone (Hm), calibration data forHprobemeasured in the anechoic chamber is used. From this example figure it can be seen that there is virtually no difference between the measurements made in the two environments. The range between the maximum and minimum frequency point values is slightly higher in the magnitude and phase delay responses for measurements made in the control room. This may be the result of higher background noise levels in the control room compared to the anechoic chamber. The confidence intervals for the measurements in both environments are relatively low and similar. This means that the measurements were consistent and reliable, with a maximum variation of 0.2 dB in magnitude and 2 degrees in phase. Thus the embodiments described herein (the IMPro method) demonstrates considerable robustness against variations in measurement environment. These example results show that pressure frequency response measurements obtained in a typical office environment closely resemble those acquired in an anechoic chamber. Whilst an anechoic chamber remains the ideal setting for acoustic measurements, the comparable results achieved in a more modest office environment highlight the embodiment’s ability to produce reliable data even under less controlled acoustic conditions. Figs.7a to 7c present the free-field directional response (Hf) of the sphere microphone, generated using the embodiments described herein, alongside directly measured responses from the anechoic chamber (Hff). Both the free-field and the embodiments data were smoothed using 1 / 36th octave smoothing, and the deviations from linear phase responses are shown for clarity. The embodiments accurately predicts the free-field response for incident angles up to 90°, closely matching the measured data. The differences in the responses of the sphere microphone for rotation angles between 0° and 60° are so similar that only the 0° on-axis data is illustrated. For a rotation of 180°, the embodiments described herein fail to accurately predict the peak in the magnitude response, and the phase response exhibits some discrepancies at high frequencies. This discrepancy can be attributed to a combination of factors. Fig.5 for example shows a dip in the analytical external pressure at the probe measurement point near 4 kHz, coinciding with a resonance in the sphere microphone’s pressure response. These resonances are independent, with the microphone resonance caused by the coupling of the sound port and capsule, and the external pressure dip resulting from the sphere’s size and distance from the source. The gradients for both responses at 4 kHz are steep, and so small shifts in the frequency of these resonances can lead to errors.

[0156] With respect to Fig.8a to Fig.8d there are shown schematically example apparatus for implementing some embodiments.

[0157] For example, Fig.8a shows the measurement source (which is an effective linear transducer e.g. the loudspeaker or LS) which generates acoustic radiation 717 to the device under test (DUT) microphone recorder 703 and also to the probe microphone recorder 707.

[0158] The measurement source may or may not be separate from the integrated microphone DUT or from the probe microphone.

[0159] As discussed above the device under test (DUT) microphone recorder 703 is configured to obtain at least one audio signal from the integrated microphone based on a transduction of the acoustic wave (generated based on the measurement source audio signal or measurement audio signal or loudspeaker audio signal).

[0160] As shown in Fig.8a the DUT microphone recorder 703 is configured to synchronize the generated at least one audio signal from the integrated microphone (the microphone under test) based on a synchronization signal from the measurement source 701.

[0161] Additionally the output of the DUT microphone recorder 703 and the measurement source audio signal from the measurement source LS 701 are passed to an integrated microphone response determiner 705 which is configured to determine the value according to the embodiments described above. Although in this example the property is thevalue. The property determined can be any suitable property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal. For example, this property can be at least one of: a total harmonic distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an acoustic overloading point of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a signal to noise ratio of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone noise floor of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone spectral distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone signal cross-correlation of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; an integrated microphone signal coherence of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a transfer function of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; a frequency response of the integrated microphone with respect to the measurement audio signal and / or at least one measurementmicrophone audio signal; and a time domain impulse response of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal. In some embodiments the measurement audio signal determinations are applied in environments such as an anechoic chamber and the measurement microphone audio signals used in reverberant rooms where the measurement microphone is of sufficient quality. For example, in embodiments employing a high quality probe microphone as a measurement microphone. In these embodiments the integrated microphone response determiner 705 is configured to receive the measured microphone audio signal, for example from the probe microphone recorder (and thus in some embodiments the operation of determining the first property can be implemented after the obtaining of the at least one audio signal from the probe microphone (or more generally from the measurement microphone).

[0162] Furthermore the probe microphone recorder 707 is configured to obtain at least one audio signal from the probe microphone based on a transduction of the acoustic wave (generated based on the measurement audio signal).

[0163] As shown in Fig.8a the probe microphone recorder 707 is configured to synchronize the generated at least one audio signal from the probe microphone based on a synchronization signal 715 from the measurement source 701.

[0164] Additionally the output of the probe microphone recorder 707 and the measurement source audio signal from the measurement source LS 701 are passed to a probe microphone response determiner 709 which is configured to determine the Hpvalue according to the embodiments described above.

[0165] Although this determined property is a transfer function, the property could be any of the following: a total harmonic distortion of the measurement microphone with respect to the measurement audio signal; an acoustic overloading point of the measurement microphone with respect to the measurement audio signal; a signal to noise ratio of the measurement microphone with respect to the measurement audio signal; an integrated microphone noise floor of the measurement microphone with respect to the measurement audio signal; an integrated microphone spectral distortion of the measurement microphone with respect to the measurement audio signal; an integrated microphone signal cross-correlation of the measurement microphone with respect to the measurement audio signal; an integrated microphone signal coherence of the measurement microphone with respect to the measurement audio signal; a frequency response of the measurement microphone with respect to the measurement audio signal; and a time domain impulse response of the measurement microphone with respect to the measurement audio signal.

[0166] The outputs from the probe microphone response determiner 709 and the integrated microphone response determiner 705 can then be passed to an integrated microphone pressure frequency response determiner configured to generate the integrated microphone pressure frequency response Hmbased on the , and H values.

[0167] For example, the right hand side of Fig.8a shows the calibration sound source (which can also be an effective linear transducer e.g. the loudspeaker or LS) which generates acoustic radiation 727 to the reference microphone recorder 731 and also to the probe microphone recorder 733.

[0168] As discussed above the reference microphone recorder 731 is configured to obtain at least one audio signal from the reference microphone based on a transduction of the acoustic wave (generated based on the calibration source audio signal).

[0169] As shown in Fig.8a the reference microphone recorder 731 is configured to synchronize the generated at least one audio signal from the reference microphone based on a synchronization signal 727 from the calibration sound source 721.

[0170] Additionally the output of the calibration microphone recorder 731 and the calibration sound source audio signal from the calibration sound source 721 are passed to a reference microphone response determiner 735 which is configured to determine the Hrvalue according to the embodiments described above. Although this determined property is a transfer function, the property could be any of the following: a total harmonic distortion of the reference microphone with respect to the calibration source audio signal; an acoustic overloading point of the reference microphone with respect to the calibration source audio signal; a signal to noise ratio of the reference microphone with respect to the calibration source audio signal; an integrated microphone noise floor of the reference microphone with respect to the calibration source audio signal; an integrated microphone spectral distortion of the reference microphone with respect to the calibration source audio signal; an integrated microphone signal cross-correlation of the reference microphone with respect to the calibration source audio signal; an integrated microphone signal coherence of the of the reference microphone with respect to the calibration source audio signal; a frequency response of the reference microphone with respect to the reference source audio signal; and a time domain impulse response of the reference microphone with respect to the measurement audio signal.

[0171] Furthermore the probe microphone recorder 733 (which can be same recorder 707) is configured to obtain at least one audio signal from the probe microphone based on a transduction of the acoustic wave (generated based on the calibration sound source audio signal).

[0172] As shown in Fig.8a the probe microphone recorder 733 is configured to synchronize the generated at least one audio signal from the probe microphone based on a synchronization signal 725 from the measurement source 701.

[0173] Additionally the output of the probe microphone recorder 733 and the measurement source audio signal or measurement audio signal more generally from the calibration sound source 721 are passed to a probe microphone calibration response determiner 737 which is configured to determine the Hcvalue according to the embodiments described above. Although this determined property is a transfer function, the property could be any of the following: a total harmonic distortion of the measurement microphone withrespect to the calibration source audio signal; an acoustic overloading point of the measurement microphone with respect to the calibration source audio signal; a signal to noise ratio of the measurement microphone with respect to the calibration source audio signal; an integrated microphone noise floor of the measurement microphone with respect to the calibration source audio signal; an integrated microphone spectral distortion of the measurement microphone with respect to the calibration source audio signal; an integrated microphone signal cross-correlation of the measurement microphone with respect to the calibration source audio signal; an integrated microphone signal coherence of the measurement microphone with respect to the calibration source audio signal; a frequency response of the measurement microphone with respect to the calibration source audio signal; and a time domain impulse response of the measurement microphone with respect to the calibration source audio signal.

[0174] Furthermore there is shown a Srefdeterminer 739 configured to obtain or determine the Srefvalue and pass this to a reference microphone response determiner 735. Srefis the output signal level of the reference microphone when exposed to a known input acoustic pressure. It is determined by the use of a microphone calibrator device which produces a known sound pressure absolute.

[0175] The outputs from the probe microphone calibration response determiner 737 and the reference microphone response determiner 735 can then be passed to a calibration probe response determiner configured to generate the calibration probe response Hprobebased on the Hc, Srefand Hrvalues in a manner such as shown above. The measurement microphone calibration property can comprise at least one of: a measurement microphone calibration signal total harmonic distortion; a measurement microphone calibration acoustic overloading point; a measurement microphone calibration signal to noise ratio; a measurement microphone calibration noise floor; a measurement microphone calibration spectral distortion; a measurement microphone calibration signal cross-correlation; a measurement microphone calibration signal coherence; a measurement microphone calibration transfer function such as detailed above; a measurement microphone calibration frequency response; and a measurement microphone calibration time domain impulse response.

[0176] Fig.8b furthermore shows a further example of the apparatus according to some embodiments. The difference between the configurations shown in Fig.8a and 8b is that the apparatus in Fig.8b does not feature the DUT microphone recorder 703 receiving the synchronization information from the measurement source 701. However, in this example following the integrated microphone response determiner 705 which is configured to determine thevalue there is employed an integrated microphone response time aligner 801 which is configured to receive thevalue and also receive synchronization information from the probe microphone response determiner 709. For the operation of the time aligner 801 it is important that time alignment is done consistently in repeated measurements. Time aligner can be implemented using a method known in art for alignment of frequency responses or impulse responses. This synchronization informationcan then be employed to time align the Hi value and pass the time aligned value to the integrated microphone pressure frequency response determiner 711.

[0177] Fig.8c furthermore shows another example of the apparatus according to some embodiments. The difference between the configurations shown in Fig.8a and 8c is that the apparatus in Fig.8c does not feature the DUT microphone recorder 703 receiving the synchronization information from the measurement source 701. However, in this example after the integrated microphone response determiner 705 which is configured to determine thevalue there is employed a microphone signal time aligner controller 901 which is configured to receive thevalue and also receive synchronization information from the probe microphone response determiner 709. This synchronization information can then be employed to generate a microphone signal time alignment control signal which is passed to a microphone signal time aligner 903, which is configured to receive the output of the DUT microphone recorder 703 and time align the integrated microphone audio signals and pass the time aligned microphone signals to the integrated microphone response determiner 705.

[0178] Fig.8d furthermore shows another example of the apparatus according to some embodiments. The difference between the configurations shown in Fig.8a and 8d is that the apparatus in Fig.8d does not feature the synchronization information from the measurement source 701 orcalibration sound source 721. However, in this example there is an external synchronization source 1001 which is configured to generate synchronization information for the measurement source 701, DUT microphone recorder 703 and the probe microphone recorder 707 and a further external synchronization source 1003 which is configured to generate synchronization information for the calibration sound source 721, reference microphone recorder 731 and the probe microphone recorder 733.

[0179] Fig.8e furthermore shows another example of the apparatus to some embodiments. The difference between the configurations shown in Fig.8a and 8c is that the apparatus in Fig.8e does not feature the DUT microphone recorder 703 receiving the synchronization information from the measurement source 701. However, in this example after the integrated microphone response determiner 705 which is configured to determine the value there is employed a microphone signal time aligner controller 1101 which is configured to receive thevalue and also receive synchronization information from the DUT microphone recorder 703 and the probe microphone recorder 707. The difference here is that time alignment is not made from transfer functions but from recorded signals, for example using known signal cross-correlation methods. The microphone signal time aligner controller 1101 is configured to generate a microphone signal time alignment control signal which is passed to a microphone signal time aligner 1103, which is configured to receive the output of the DUT microphone recorder 703 and time align the integrated microphone audio signals and pass the time aligned microphone signals to the integrated microphone response determiner 705.

[0180] With respect to Fig.9 is shown a flow diagram of the operations of the apparatus according to some embodiments.

[0181] Thus, for example, as shown by 1101, is the operation of generating an acoustic wave based on a measurement audio signal from loudspeaker.

[0182] Following this is the operation as shown by 1103 of obtaining at least one audio signal from an integrated microphone, the at least one audio signal from the integrated microphone based on a detection of an acoustic wave generated based on a measurement source audio signal.

[0183] Following this as shown by 1105, is the operation of determining a first property (for example a transfer function) based on the at least one audio signal from the integrated microphone and the measurement source audio signal.

[0184] Additionally is the operation, as shown by 1107, of obtaining at least one audio signal from a probe microphone, the probe microphone located substantially close to a sound inlet of the integrated microphone, the at least one audio signal from the probe microphone based on a detection of the acoustic wave from the measurement source audio signal.

[0185] This is followed by the operation, as shown by 1109, of determining a second property (for example a transfer function) based on the at least one audio signal from the probe microphone and the measurement source audio signal.

[0186] Further as shown by 1111 is the operation of determining an integrated microphone pressure frequency response based on the first property and the second property function. Although in this example the integrated microphone characteristic being determined is the integrated microphone pressure frequency response, in other embodiments the integrated microphone characteristic being determined can be at least one of the following: an integrated microphone pressure time domain impulse response (the time domain equivalent to the frequency response); an integrated microphone signal total harmonic distortion which is able to provide microphone information for multi-tone distortion analysis; an integrated microphone acoustic overloading point; an integrated microphone signal to noise ratio which assumes the measurement is performed in quiet acoustic environment; an integrated microphone noise floor which also assumes the measurement is performed in a quiet acoustic environment; an integrated microphone spectral distortion; an integrated microphone signal cross-correlation; and an integrated microphone signal coherence.

[0187] In some embodiments the integrated microphone can be a derived quality metric such as: Speech Transmission Index (STI), Mean Opinion Score (MOS) (in different versions), Perceptual Evaluation of Speech Quality (PESO), Perceptual Objective Listening Quality Assessment (POLQA).

[0188] In some embodiments where the speaker is integrated with the device under test the characteristic can be an Echo Return Loss Enhancement (ERLE).

[0189] In some embodiments the transfer function between sound source and the integrated microphone can also be interpreted in the context of communication devices as an echo path. Acoustic echo cancellation (AEC) algorithms can be employed to estimate this transfer function adaptively in real-time, but the same transfer function estimation can be also implemented using the methods described herein. When transfer functions are estimated from the loudspeaker source to probe microphone and from loudspeaker to integrated microphone the AEC algorithm modeling performance can be used as an indicator for acoustic feedback system linearity. The difference between these two transfer functions can provide valuable information about the quality of microphone integration. In the case of integrated loudspeaker the transfer function to probe microphone does not include contributions from possible mechanical coupling between loudspeaker and microphone whereas the transfer function from loudspeaker to integrated can include contributions mechanical coupling such as mechanical vibrations and sound conduction, or leakage, inside the body of the device. The AEC performance, that is typically measured as Echo Return Loss Enhancement (ERLE), is an important quality attribute for communication devices and therefore can be considered as a quality metric, because ERLE performance is compromised by microphone distortions and interfering noises.

[0190] In some embodiments the integrated microphone characteristic can comprise complementary measurements that measure environment characteristics that are not directly related to microphone characterization but measurement signal selection, such as Reverberation time or Acoustic delay.

[0191] In some embodiments therefore the transfer function estimation can indicate the characteristics or performance between the integrated loudspeaker and integrated microphone or an Echo Return Loss Enhancement (ERLE) estimation performance between integrated loudspeaker and integrated microphone;

[0192] Furthermore as a design task in microphone integration is the protection against electromagnetic interferences (EMI) from surrounding electronic components some embodiments of the following can aim to address testing for EMI. This type of interference causes issues with respect to product audio quality and any noise sources generated by EMI should be, where possible, eliminated. In some embodiments as the measurement microphone, such as a probe microphone, is typically well protected against EMI then employing the apparatus and methods as described herein can enable noise floor analysis comparing measurement or probe microphone signals and integrated microphone signals to test for possible EMI. In some embodiments the apparatus and methods can similarly be used to investigate other possible EMI noise sources such as from other sensors like camera modules that have typically active components. For example, camera modules can be equipped with automatic zoom and autofocus moving optical lens systems with ‘optical’ actuators potentially generating EMI. These optical actuators for example can introduce both mechanical and electrical interferences that can disturb integrated microphones

[0193] Thus, in some embodiments, a property to be determined can be electrical interference to integrated microphone with respect to the measurement microphone or (reference) probe microphone audio signal.Furthermore in some embodiments can be interference from mechanical or optical actuators to integrated microphone audio signals with respect to the measured microphone or (reference) probe audio signal.

[0194] Furthermore as shown in Fig.10 is a flow diagram relating to the calibration of the probe microphone and the application of the calibration to the determination of the integrated microphone pressure frequency response.

[0195] Thus for example as shown Fig.10 by 1201, is the operation of generating an acoustic wave based on a calibration source audio signal from loudspeaker.

[0196] Following on, as shown in Fig.10 by 1203, is the operation of obtaining at least one audio signal from a reference microphone, the at least one audio signal from the reference microphone based on a detection of an acoustic wave generated based on a calibration sound source audio signal.

[0197] This can be followed, as shown in Fig.10 by 1205, is the operation of determining a first calibration property (for example a transfer function) based on the at least one audio signal from the reference microphone and the calibration sound source audio signal.

[0198] Furthermore is shown in Fig.10 by 1207, the operation of obtaining at least one further audio signal from the probe microphone, the probe microphone located substantially close to a sound inlet of the calibration microphone, the at least one further audio signal from the probe microphone based on a detection of the acoustic wave from the calibration sound source audio signal.

[0199] This can then be followed by the operation, as shown in Fig.10 by 1209, of determining a second calibration property (for example transfer function) based on the at least one audio signal from the probe microphone and the calibration sound source audio signal.

[0200] Then is the operation, as shown in Fig.10 by 1211, of determining a probe calibration transfer function or more generally a probe calibration property based on the first calibration property (transfer function) and the second calibration property (transfer function), wherein determining the integrated microphone pressure frequency response based on the first property (transfer function) and the second property (transfer function) further comprises determining the integrated microphone pressure frequency response based on the probe calibration transfer function.

[0201] In the embodiments as discussed there can be a similarity respect to the design of the microphone port geometry and probe tip geometry. For example simple structures can avoid unnecessary perturbations to sound fields and therefore edges can be avoided.

[0202] In some embodiments the measurements or properties can be sensitivity measurement or multitone measurements which can be considered as sparse frequency response measurement.

[0203] Furthermore in some embodiments a distortion measurement for the integrated microphone could be implemented using the embodiments as described herein, but in such embodiments the noise floor orSNR measurement would require a very low noise environment (or preferably a silent environment), for example by eliminating background noise.

[0204] In some embodiments the echo path between an integrated loudspeaker and an integrated microphone could be characterized in part using the process described.

[0205] The embodiments as described herein are suitable for measuring microphones integrated in a wall or some other construction, as it is not possible to ‘locate’ such an integration within a test lab.

[0206] Another suitable real world case would be an automotive scenario for measuring 10 microphones in a car or vehicle interior with different integration mechanics. In some embodiments it is possible to measure each microphone one by one as it is difficult to simulate otherwise because the sound field inside a car is very sensitive to position inside the car.

[0207] The embodiments can furthermore be applied to quality control or maintenance of integrated microphones for devices in the field or returned for servicing or for repair.

[0208] With respect to Fig.11 an example electronic device which may be used as the apparatus 341 or any of the functional blocks described herein is shown. The device may be any suitable electronics device or apparatus. For example in some embodiments the device 1900 / 341 is a mobile device, user equipment, tablet computer, computer, audio playback apparatus, car or other vehicle, loT device, etc.

[0209] In some embodiments the device 1900 comprises at least one processor or central processing unit 1907. The processor 1907 can be configured to execute various program codes such as the methods such as described herein.

[0210] In some embodiments the device 1900 comprises a memory 1911. In some embodiments the at least one processor 1907 is coupled to the memory 1911. The memory 1911 can be any suitable storage means. In some embodiments the memory 1911 comprises a program code section for storing program codes implementable upon the processor 1907. Furthermore in some embodiments the memory 1911 can further comprise a stored data section for storing data, for example data that has been processed or to be processed in accordance with the embodiments as described herein. The implemented program code stored within the program code section and the data stored within the stored data section can be retrieved by the processor 1907 whenever needed via the memory-processor coupling.

[0211] In some embodiments the device 1900 comprises a user interface 1905. The user interface 1905 can be coupled in some embodiments to the processor 1907. In some embodiments the processor 1907 can control the operation of the user interface 1905 and receive inputs from the user interface 1905. In some embodiments the user interface 1905 can enable a user to input commands to the device 1900, for example via a keypad. In some embodiments the user interface 1905 can enable the user to obtain information from the device 1600. For example the user interface 1905 may comprise a display configured to display information from the device 1900 to the user. The user interface 1905 can in some embodiments comprise atouch screen or touch interface capable of both enabling information to be entered to the device 1900 and further displaying information to the user of the device 1900.

[0212] In some embodiments the device 1900 comprises an input / output port 1901. The input / output port 1901 in some embodiments comprises a digital to analogue converter for receiving or outputting audio signals, for example receiving the microphone audio signals from the probe microphone 303 or integrated microphone 311 and / or outputting the loudspeaker audio signal to the loudspeaker 301. In some embodiments this can be a wired or wireless (for example Bluetooth) connection.

[0213] Additionally in some embodiments the device 1900 comprises a transceiver 1909. The transceiver 1909 and input / output port 1901 in such embodiments can be coupled to the processor 1907.

[0214] The transceiver 1909 in some embodiments can be configured to enable a communication with other apparatus or electronic devices, for example via a wireless communications network. The transceiver or any suitable transceiver or transmitter and / or receiver means can in some embodiments be configured to communicate with other electronic devices or apparatus via a wire or wired coupling.

[0215] The transceiver can communicate with further apparatus by any suitable known communications protocol.

[0216] It should be understood that the apparatuses may comprise or be coupled to other units or modules used in or for transmission and / or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

[0217] It is noted that whilst some embodiments have been described in relation to 5G networks, similar principles can be applied in relation to other networks and communication systems. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

[0218] It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

[0219] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0220] In general, the various embodiments may be implemented in hardware or special purpose circuitry, software, logic or any combination thereof. Some aspects of the disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While variousaspects of the disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0221] As used in this application, the term “circuitry” may refer to one or more or all of the following:(a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and(b) combinations of hardware circuits and software, such as (as applicable):(c) a combination of analog and / or digital hardware circuit(s) with software / firmware and (i) any portions of hardware processor(s) with 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(ii) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0222] 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 also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0223] The embodiments of this disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and / or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer-executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

[0224] Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memorychips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as DVD and the data variants thereof, CD. The physical media is a non-transitory media.

[0225] The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0226] The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

[0227] Embodiments of the disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

[0228] The scope of protection sought for various embodiments of the disclosure is set out by the independent claims. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the disclosure.

[0229] The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this disclosure will still fall within the scope of this invention as defined in the appended claims. Indeed, there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

39CLAIMS1. An apparatus for determining an integrated microphone characteristic, the apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the system at least to:obtain at least one audio signal from an integrated microphone based on a measurement audio signal;obtain at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone;determine a first property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal;determine a second property based on the at least one measurement microphone audio signal and the measurement audio signal; anddetermine the integrated microphone characteristic based on the first property and the second property.

2. The apparatus as claimed in claim 1, wherein the integrated microphone characteristic comprises at least one of:an integrated microphone signal total harmonic distortion;an integrated microphone acoustic overloading point;an integrated microphone signal to noise ratio;an integrated microphone noise floor;an integrated microphone spectral distortion;an integrated microphone signal cross-correlation;an integrated microphone signal coherence;an integrated microphone pressure frequency response; andan integrated microphone pressure time domain impulse response.

3. The apparatus as claimed in any of claims 1 or 2, wherein the first property comprises at least one of:a total harmonic distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal;40an acoustic overloading point of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal;a signal to noise ratio of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal;an integrated microphone noise floor of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal;an integrated microphone spectral distortion of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal;an integrated microphone signal cross-correlation of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal;an integrated microphone signal coherence of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio si g nal ; a transfer function of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal;a frequency response of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal; anda time domain impulse response of the integrated microphone with respect to the measurement audio signal and / or at least one measurement microphone audio signal.

4. The apparatus as claimed in any of claims 1 to 3, wherein the second property comprises at least one of:a total harmonic distortion of the measurement microphone with respect to the measurement audio signal;an acoustic overloading point of the measurement microphone with respect to the measurement audio signal;a signal to noise ratio of the measurement microphone with respect to the measurement audio signal; an integrated microphone noise floor of the measurement microphone with respect to the measurement audio signal;an integrated microphone spectral distortion of the measurement microphone with respect to the measurement audio signal;an integrated microphone signal cross-correlation of the measurement microphone with respect to the measurement audio signal;an integrated microphone signal coherence of the measurement microphone with respect to the measurement audio signal;41a transfer function of the measurement microphone with respect to the measurement audio signal; a frequency response of the measurement microphone with respect to the measurement audio signal; anda time domain impulse response of the measurement microphone with respect to the measurement audio signal.

5. The apparatus as claimed in any of claims 1 to 4, wherein the measurement microphone sound-inlet is located relative to the sound inlet of the integrated microphone with a gap based on a physical size and / or geometry of the measurement microphone sound-inlet, the gap preventing the measurement microphone sound-inlet blocking or acoustic shadowing the sound inlet of the integrated microphone.

6. The apparatus as claimed in any of claims 1 to 5, wherein the measurement microphone sound-inlet is positioned such that the sound inlet of the integrated microphone and a center of the measurement microphone sound-inlet are coincident.

7. The apparatus as claimed in claim 6, wherein the measurement microphone sound-inlet is positioned such that the sound inlet of the integrated microphone and the center of the measurement microphone soundinlet are aligned to an outward surface normal of the sound inlet of the integrated microphone.

8. The apparatus as claimed in any of claims 1 to 7, further comprising:the integrated microphone;the measurement microphone; anda support structure configured to support the integrated microphone and the measurement microphone such that the measurement microphone sound-inlet is located substantially close to a sound inlet of the integrated microphone and with axes of the measurement microphone sound-inlet and sound inlet of the integrated microphone substantially aligned.

9. The apparatus as claimed in any of claims 1 to 8, further comprising the measurement source.

10. The apparatus as claimed in claim 9, wherein the measurement source comprises a loudspeaker, wherein the axes of the measurement microphone sound-inlet and sound inlet of the integrated microphone are substantially aligned with an output axis of the loudspeaker.

11. The apparatus as claimed in any of claims 1 to 10, further caused to:obtain at least one audio signal from a reference microphone, the at least one audio signal from the reference microphone based on a calibration sound source audio signal;obtain at least one further measurement microphone audio signal from the measurement microphone based on the calibration sound source audio signal, the measurement microphone sound-inlet configured to be substantially aligned and located relative;determine a first calibration property based on the at least one audio signal from the reference microphone and the calibration sound source audio signal;determine a second calibration property based on the at least one further measurement microphone audio signal and the calibration sound source audio signal;determine a measurement microphone calibration response based on the first calibration property and the second calibration characteristic, wherein the apparatus caused to determine the integrated microphone characteristic based on the first property and the second property is caused to determine the integrated microphone characteristic based on the measurement microphone calibration response.

12. The apparatus as claimed in claim 11, wherein the at least one audio signal from the reference microphone is based on a transduction of an acoustic wave generated from a calibration sound source; and the at least one further measurement microphone audio signal is based on a transduction of an acoustic wave generated from the calibration sound source.

13. The apparatus as claimed in any of claims 11 or 12, wherein the measurement microphone calibration property comprises at least one of:a measurement microphone calibration signal total harmonic distortion;a measurement microphone calibration acoustic overloading point;a measurement microphone calibration signal to noise ratio;a measurement microphone calibration noise floor;a measurement microphone calibration spectral distortion;a measurement microphone calibration signal cross-correlation;a measurement microphone calibration signal coherence;a measurement microphone calibration transfer function;a measurement microphone calibration frequency response; anda measurement microphone calibration time domain impulse response.

14. The apparatus as claimed in any of claims 11 to 13, wherein the first calibration property comprises at least one of:a total harmonic distortion of the reference microphone with respect to the calibration source audio signal;an acoustic overloading point of the reference microphone with respect to the calibration source audio signal;a signal to noise ratio of the reference microphone with respect to the calibration source audio signal; an integrated microphone noise floor of the reference microphone with respect to the calibration source audio signal;an integrated microphone spectral distortion of the reference microphone with respect to the calibration source audio signal;an integrated microphone signal cross-correlation of the reference microphone with respect to the calibration source audio signal;an integrated microphone signal coherence of the of the reference microphone with respect to the calibration source audio signal;a transfer function of the reference microphone with respect to the calibration source audio signal; a frequency response of the reference microphone with respect to the reference source audio signal; anda time domain impulse response of the reference microphone with respect to the measurement audio signal.

15. The apparatus as claimed in any of claims 11 to 14, wherein the second calibration property comprises at least one of:a total harmonic distortion of the measurement microphone with respect to the calibration source audio signal;an acoustic overloading point of the measurement microphone with respect to the calibration source audio signal;a signal to noise ratio of the measurement microphone with respect to the calibration source audio signal;an integrated microphone noise floor of the measurement microphone with respect to the calibration source audio signal;an integrated microphone spectral distortion of the measurement microphone with respect to the calibration source audio signal;an integrated microphone signal cross-correlation of the measurement microphone with respect to the calibration source audio signal;44an integrated microphone signal coherence of the measurement microphone with respect to the calibration source audio signal;a transfer function of the measurement microphone with respect to the calibration source audio signal;a frequency response of the measurement microphone with respect to the calibration source audio signal; anda time domain impulse response of the measurement microphone with respect to the calibration source audio signal.

16. The apparatus as claimed in any of claims 1 to 15, further caused to at least one of:align the second property based on the at least one measurement microphoneaudio signal and the measurement audio signal with the first property function based on the at least one audio signal from the integrated microphone and the measurement audio signal;align the at least one audio signal from the integrated microphone with the at least one measurement microphone audio signal based on a comparison between the first property based on the at least one audio signal from the integrated microphone and the second property based on the at least one measurement microphone audio signal;align the at least one audio signal from the integrated microphone with the at least one measurement microphone audio signal based on a comparison between the first property; the at least one audio signal from the integrated microphone and the at least one measurement microphone audio signal; andalign the measurement audio signal, the at least one audio signal from the integrated microphone, and the at least one measurement microphone audio signal based on an obtained synchronization signal, wherein the synchronization signal is obtained from one of: the measurement source; and a synchronization source.

17. The apparatus as claimed in claim 16 when dependent on claim 11, wherein the synchronization signal further synchronizes the at least one audio signal from the reference microphone and the at least one further measurement microphone audio signal.

18. The apparatus as claimed in any of claims 1 to 17, wherein the at least one audio signal from the integrated microphone is based on a transduction of an acoustic wave generated from the measurement source; and the at least one measurement microphone audio signal is based on a transduction of the acoustic wave from the measurement source.4519. The apparatus as claimed in any of claims 1 to 18, wherein the measurement microphone is a probe microphone, wherein the probe microphone comprises one of:a probe-tip located substantially close to the sound inlet of the integrated microphone and with axes of a sound-inlet of the probe-tip and the sound inlet of the integrated microphone substantially aligned; and no probe-tip located substantially close to the sound inlet of the integrated microphone and with axes of a sound-inlet of the probe microphone and the sound inlet of the integrated microphone substantially aligned.

20. A method for an apparatus for determining an integrated microphone characteristic, the method comprising:obtaining at least one audio signal from an integrated microphone based on a measurement audio signal;obtaining at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone;determining a first property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal;determining a second property based on the at least one measurement microphone audio signal and the measurement audio signal; anddetermining the integrated microphone characteristic based on the first property and the second property.

21. An apparatus for determining an integrated microphone characteristic, the apparatus comprising means configured to:obtain at least one audio signal from an integrated microphone based on a measurement audio signal;obtain at least one measurement microphone audio signal from a measurement microphone based on the measurement audio signal, the measurement microphone comprising a sound inlet configured to be substantially aligned and located relative to a sound inlet of the integrated microphone;determine a first property based on the at least one audio signal from the integrated microphone and the measurement audio signal and / or at least one measurement microphone audio signal;determine a second property based on the at least one measurement microphone audio signal and the measurement audio signal; and46determine the integrated microphone characteristic based on the first property and the second property.

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