Devices and methods for determining an acoustic response of a human ear canal

Abstract

A control device (100) is disclosed for controlling a set of earphones. The control device (100) is configured to determine a transfer function between a loudspeaker of an earphone of the set of earphones and a microphone of the earphone. Moreover, the control device (100) is configured to determine a plurality of ratios of the transfer function in a plurality of frequency bands and to determine, based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets one or more quality criteria.

Description

[0001] Devices and methods for determining an acoustic response of a human ear canal

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to audio technology. More specifically, the present disclosure relates to devices and methods for determining an acoustic response of a human ear canal.

[0004] BACKGROUND

[0005] The ear canal, or external auditory canal, is a tube-like structure that connects the outer ear to the middle ear. It plays a crucial role in the auditory system. As it guides the sound towards the ear drum, the shape and length of the ear canal can enhance certain frequencies of sound, contributing to the overall perception of sound quality. Individual variations of the ear canal properties (shape, length, diameter) influence individual differences in the sound pressure at the ear drum and makes hearing sound a highly individual experience.

[0006] When listening to sound using insert-ear earphones (also referred to as earbuds, in-ears, hearing aids, and the like) it is important to understand the acoustic properties of the ear canal of the user of that device to be able to achieve an optimal listening experience. Therefore, it is desired to obtain acoustic measurements in the ear canal by emitting sound from the acoustic transducer (loudspeaker) of an earphone and recording the acoustic response using a microphone mounted to the earphone within the acoustic volume formed by the ear canal.

[0007] Measuring acoustic responses is well known in controlled laboratory settings, but in vivo measurements of earphones within human ear canals pose significant challenges due to several factors. For instance, variations of the acoustic coupling between the earphone and the ear canal caused by fitting variations lead to strong degradations of the sound pressure which can be measured in the ear canal. The individual variations of the ear canal shape and the insertion depth which adds resonances and can create strong variations of the measured responses. The ear canal is a dynamic environment where factors such as movement, changes in pressure, and the presence of earwax can influence acoustic measurements. An unpredictable behaviour or movement of the user can add strong air-conducted noise, bone-conducted interferences or other noises resulting from the activity of the user.

[0008] Therefore, there is a need for providing means to obtain reliable acoustic measurements of an earphone inserted into the ear canal of users which are robust to a wide variety of factors which can lead to degradations of the quality of the measurement.

[0009] US11722809B2 discloses an approach for detecting a non-optimum fitting of earphones based on acoustic measurements. If the fitting is not well (e.g. due to using too small ear tips) air leaks allow acoustic pressure to equalize. This results in a strong attenuation of the measured low frequency response in the ear canal. The approach disclosed in US11722809B2 uses this observation to detect if the seal provided by the current ear tip is good enough or not. To this end, two frequency ranges are defined (high and low) and acoustic responses (intensities) are compared with defined thresholds (target response). The approach disclosed in US11722809B2 is relying on an absolute target function which needs to be defined beforehand. However, as the acoustic response in the ear-canal depends on the physical parameters of the individual human ear canal, it is difficult to define an absolute target. In particular for mid and high frequencies, the individual variations are affecting the measured response significantly.

[0010] SUMMARY OF THE INVENTION

[0011] It is an objective of the present disclosure to provide improved devices and methods for determining an acoustic response of a human ear canal.The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

[0012] According to a first aspect a control device is provided for controlling a set of earphones (also referred to as in-ear headphones). The control device according to the first aspect is configured to determine a transfer function of a signal path between a loudspeaker of an earphone of the set of earphones and a microphone of the earphone. Moreover, the control device according to the first aspect is configured to determine a plurality of ratios of the transfer function in a plurality of different frequency bands and to determine, based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets one or more quality criteria. In other words, the control device according to the first aspect uses the plurality of ratios of the transfer function in a plurality of different frequency bands as quality measures for determining the quality of the transfer function. Thus, the control device according to the first aspect allows determining the quality of an acoustic response of the human ear canal in a robust manner.

[0013] In a further possible implementation form, the control device according to the first aspect is configured to determine, based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets one or more quality criteria, for determining whether the transfer function is of sufficient quality for adjusting an audio signal to be rendered by the earphone and / or for identifying a wearer of the set of earphones.

[0014] In a further possible implementation form, the control device according to the first aspect is configured to determine the transfer function based on an in-vivo measurement of an acoustic response. Thus, the control device according to the first aspect may be used for obtaining an acoustic response of the set of earphones in a human ear canal.

[0015] In a further possible implementation form, the control device according to the first aspect is configured to continuously or periodically determine the transfer function of a signal path based on an in-vivo measurement of an acoustic response to an audio signal rendered by the earphone and to continuously or periodically adjust the audio signal rendered by the earphone based on the transfer function, if the transfer function meets one or more quality criteria for adjusting the audio signal rendered by the earphone. Thus, the control device according to the first aspect may be used for determining changes of the acoustic response of the human ear canal over time.

[0016] In a further possible implementation form, the control device according to the first aspect is configured to signal to a wearer of the set of earphones to adjust the fitting of the set of earphones and / or to avoid interferences, i.e. external noise sources, when obtaining the transfer function, if the transfer function does not meet the one or more quality criteria. Thus, the wearer is able to react and perform necessary actions for improving the quality of the transfer function in subsequent measurements.

[0017] In a further possible implementation form, if the transfer function does not meet the one or more quality criteria, the control device is configured to:

[0018] determine a further transfer function of a signal path between the loudspeaker of the earphone of the set of earphones and the microphone of the earphone;

[0019] determine a plurality of further ratios, i.e. quality measures of the further transfer function in the plurality of frequency bands; and

[0020] determine, based on the plurality of further ratios of the further transfer function in the plurality of frequency bands, whether the further transfer function meets the one or more quality criteria. Thus, the control device according to the first aspect allows determining a transfer function response of the human ear canal in a robust manner even when degradations and interferences affect the quality of the transfer function.In a further possible implementation form, the control device is configured to determine, based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets the one or more quality criteria by comparing the plurality of ratios with a plurality of ratio thresholds. Thus, an absolute threshold of the transfer function is not required and the robustness to individual variations and degradations is improved.

[0021] In a further possible implementation form, the plurality of ratios of the transfer function in the plurality of frequency bands comprises a first ratio between the transfer function in a high frequency band and the transfer function in a mid frequency band and a second ratio between the transfer function in the high frequency band and the transfer function in a low frequency band. Thus, by considering multiple ratios in different frequency bands more robust quality criteria may be achieved.

[0022] In a further possible implementation form, the control device according to the first aspect is configured to determine whether the first ratio is larger than the second ratio for determining whether the transfer function meets the one or more quality criteria. Thus, degradations influencing the quality of the transfer function may be effectively detected.

[0023] In a further possible implementation form, the control device according to the first aspect is further configured to determine a standard deviation of the transfer function in at least one of the plurality of frequency bands and to determine, based on the plurality of ratios of the transfer function in the plurality of frequency bands and based on the standard deviation of the transfer function in at least one of the plurality of frequency bands, whether the transfer function meets the one or more quality criteria. Thus, variations of the transfer function caused by movements of the user are effectively detected.

[0024] In a further possible implementation form, the plurality of frequency bands comprises a low frequency band, e.g. 200 to 500 Hz, a mid frequency band, e.g. 500 to 1000 Hz, a high frequency band, e.g. 2000 to 6000 Hz, and or a low-mid frequency band, e.g. 200 to 1000 Hz.

[0025] In a further possible implementation form, the control device according to the first aspect is a smartphone, smartwatch, or audio player.

[0026] According to a second aspect a set of earphones is provided, wherein at least one earphone of the set of earphones comprises a control device according to the first aspect.

[0027] According to a third aspect an audio assembly is provided, comprising a set of earphones and a control device according to the first aspect.

[0028] According to a fourth aspect a method is provided for controlling a set of earphones, i.e. in-ear headphones, wherein the method according to the fourth aspect comprises the steps of:

[0029] determining a transfer function of a signal path between a loudspeaker of an earphone of the set of earphones and a microphone of the earphone;

[0030] determining a plurality of ratios of the transfer function in a plurality of different frequency bands; and

[0031] determining, based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets one or more quality criteria.

[0032] The method according to the fourth aspect can be performed by the control device according to the first aspect. Thus, further features of the method according to the fourth aspect result directly from the functionality of the control device according to the first aspect, as well as its different implementation forms described above and below.According to a fifth aspect a computer program product is provided, comprising program code which causes a computer or a processor to perform the method according to the fourth aspect, when the program code is executed by the computer or the processor.

[0033] Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

[0036] Fig. la shows a schematic diagram illustrating processing stages implemented by a control device according to an embodiment for processing a transfer function obtained with a set of earphones;

[0037] Fig. lb shows a diagram illustrating an earphone of a set of earphones according to an embodiment for obtaining a transfer function;

[0038] Fig. 2a shows a schematic diagram illustrating a spectral shape analysis stage of a control device according to an embodiment for processing a transfer function obtained with a set of earphones;

[0039] Fig. 2b shows a schematic diagram illustrating a low frequency leakage analysis stage of a control device according to an embodiment for processing a transfer function obtained with a set of earphones;

[0040] Fig. 2c shows a schematic diagram illustrating a spectral flatness analysis stage of a control device according to an embodiment for processing a transfer function obtained with a set of earphones;

[0041] Fig. 3 shows a diagram illustrating a low leakage transfer function and a high leakage transfer function obtained by a set of earphones according to an embodiment;

[0042] Figs. 4a-c show diagrams illustrating a plurality of different transfer functions obtained by a set of earphones according to an embodiment;

[0043] Fig. 5a shows a flow diagram illustrating processing steps implemented by a control device according to an embodiment for analysing a transfer function obtained by a set of earphones according to an embodiment;

[0044] Fig. 5b shows a flow diagram illustrating processing steps implemented by a control device according to an embodiment for analysing a transfer function obtained by a set of earphones according to an embodiment; and

[0045] Fig. 6 shows a flow diagram illustrating a method for operating a control device according to an embodiment for analysing a transfer function obtained by a set of earphones according to an embodiment.

[0046] In the following, identical reference signs refer to identical or at least functionally equivalent features.

[0047] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In the following description, reference is made to the accompanying figures, which form part of the disclosure, which illustrates specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

[0049] For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated inthe figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and / or aspects described herein may be combined with each other, unless specifically noted otherwise.

[0050] Figure la shows a schematic diagram illustrating processing stages implemented by a control device 100 according to an embodiment for processing a transfer function obtained with a set of earphones. Figure lb shows a diagram illustrating an earphone 160 of a set of earphones according to an embodiment for obtaining such a transfer function. In an embodiment, the control device 100 may be implemented as a smartphone, smartwatch, or audio player. According to a further embodiment, the earphone 160 may comprise the control device 100. In a further embodiment, an audio assembly may comprise the control device 100 and a set of earphones, including the earphone illustrated in figure lb.

[0051] As will be described in more detail in the following, the control device 100 is configured to use acoustic measurements obtained by a microphone 164 of the earphone 160 for estimating the acoustic transfer function between a transducer, i.e. loudspeaker 162 of the earphone 160 and the eardrum of the listener. As indicated in figure lb, the loudspeaker 162 is arranged within a body 161 of the earphone and configured to emit sound waves along a canal 163a defined by an ear tip 163 of the earphone 160, which also houses the microphone 164. The information obtained by the control device 100 may be used, for instance, for individual equalisation for improving sound quality or an improved performance of active noise cancellation systems.

[0052] As will be described in more detail in the following, the control device 100 aims to resolve technical problems related to obtaining robust measurements of a frequency response of the earphone in the human ear canal. More specifically, the control device 100 allows detecting typical measurement errors that occur when acoustic measurements are obtained using the earphone 160 inserted into the ear canal of the listener. As will be described in more detail in the following, the control device 100 according to an embodiment is capable of dealing, for instance, with the following variations affecting the measurements: the individual variations of the ear canal shape and the insertion depth which adds resonances and can create strong variations of the measured responses and make a definition of a fixed (absolute) target curve only applicable to low frequencies but not to the entire spectrum; the ear canal is a dynamic environment where factors such as movement, changes in pressure, and the presence of earwax can influence acoustic measurements; unpredictable behaviour of the user which can add strong airconducted noise, bone-conducted interferences or other noises resulting from the activity of the user.

[0053] Moreover, the control device 100 is capable of detecting whether a measurement is affected by several conditions which degrade the accuracy of the measurement, such as poor fitting ear tips leading to low sealing and air leaks, air conducted noises, bone conducted noises, self-noise of the user, and / or structure-bome sound interferences.

[0054] As will be described in more detail under reference to figure 1 a and figures 2a-c, the control device 100 implements an approach for obtaining robust acoustic measurements of earphones in human ear canals by analysing the obtained acoustic response and detecting sound leakage and interfering noise. In an embodiment, the approach implemented by the control device may consists of two main phases, namely (a) a first phase of obtaining an acoustic measurement of the transfer function between the earphone transducer 162 and the microphone 164 using a suitable measurement; and (b) a second phase of performing an analysis of the measured transfer function. The second phase may comprise: detecting if the earphone 160 is worn by the user or not; determining a measure of the quality of the measurement; and / or repeating the measurement until it meets one or more predefined requirements, if the quality of the frequency response is below a defined limit. To this end, the control device 100 illustrated in figure la comprises a frequency band separation stage 110, a spectral flatness analysis stage 120, a spectral shapeanalysis stage 130, a low frequency leakage analysis stage 140, and a quality decision stage 150. As will be described in more detail in the following, the control device 100 and one or more of its stages illustrated in figure la are configured to determine a transfer function between the loudspeaker 162 of the earphone 160 of the set of earphones and the microphone 164 of the earphone 160 and to determine a plurality of ratios of, for instance, the intensity or power of the transfer function in a plurality of different frequency bands. Moreover, the control device 100 and one or more of its stages illustrated in figure la are configured to determine, based on the plurality of ratios of the transfer function in the plurality of different frequency bands, whether the transfer function meets one or more quality criteria.

[0055] Many different solutions exist for obtaining acoustic responses characterizing the ear canal. Most relevant are transfer function measurements which characterize the transfer function (a frequency domain representation of the impulse response) between the loudspeaker 162 and the microphone 164, other acoustically relevant parameters are for example the impulse response, frequency response, or the sound pressure.

[0056] For determining the transfer function between the loudspeaker 162 and the microphone 164 of the earphone 160 a known input signal, such as a sine wave, white noise, or a sweep signal (chirp) covering a range of frequencies, may be played through the loudspeaker 162 and captured by the microphone 164. Then, a Fourier transform (e.g., Fast Fourier Transform, FFT) may be applied to both the input and output signals to convert them from the time domain to the frequency domain. Finally, the transfer function may be obtained by taking the ratio of the output signal's Fourier transform to the input signal's Fourier transform for each frequency. The transfer function allows to identify key characteristics such as gain, phase shift, resonances, and frequency response.

[0057] As will be appreciated, the transfer function H(f) is defined as the ratio of the output signal Y(f) to the input signal X(f) in the frequency domain, i.e. H(f)=X(f) / Y(f), where H(f) is the transfer function, Y(f) is the Fourier transform of the output signal, and X(f) is the Fourier transform of the input signal. Given the transfer function, obtaining the frequency response, impulse response or other acoustically relevant measures is straight forward.

[0058] As illustrated in figure la, the frequency band separation stage 110 of the control device 100 is configured to separate the measured acoustic response, i.e. transfer function, for instance, by means of suitable bandpass filters into at least three, preferably four frequency bands. In an embodiment, the frequency band separation stage 110 of the control device 100 is configured to separate the measured acoustic response, i.e. transfer function into a low frequency band (referred to as “Band 1” in figure la), a mid frequency band (referred to as “Band 2” in figure la), a high frequency band (referred to as “Band 3” in figure la), and an optional low-mid frequency band (referred to as "Band 4” in figure la). In an embodiment, the low frequency band may cover the range of frequencies from 200 to 500 Hz, the mid frequency band may cover the range of frequencies from 500 to 1000 Hz, the high frequency band may cover the range from 2000 to 6000 Hz, and / or the optional low-mid frequency band may cover the range of frequencies from 200 to 1000 Hz. As will be appreciated, the frequency band separation stage 110 of the control device 100 may cover a wide frequency range in different frequency bands which allows a detailed analysis and detection of measurement errors of the acoustic response, e.g. transfer function.

[0059] In the embodiment shown in figure la the spectral shape analysis stage 130 (which is illustrated in more detail in figure 2a) of the control device 100 takes as input the low (Band 1), mid (Band 2) and high (Band 3) frequency band portion of the measured acoustic response, i.e. transfer function. In each of these frequency bands, the spectral shape analysis stage 130 is configured to determine a measure of sound intensity (or magnitude or power or sound pressure level) of the acoustic response, i.e. transfer function, for instance, by forming an average (or sum) over the frequency coefficients in the respective frequency band. Furthermore, as illustrated in figure 2a, the spectral shape analysis stage 130 of the control device 100 is configured to determine a plurality of ratios of the transfer function in the different frequency bands. More specifically, a processing block 134 of thespectral shape analysis stage 130 of the control device 100 is configured to determine a first ratio between, for instance, the sound intensity of the transfer function in the high (Band 3) frequency band portion and the sound intensity of the transfer function in the low (Band 1) frequency band portion. Moreover, a processing block 132 of the spectral shape analysis stage 130 of the control device 100 is configured to determine a second ratio between, for instance, the sound intensity of the transfer function in the high (Band 3) frequency band portion and the sound intensity of the transfer function in the mid (Band 2) frequency band portion. As will be appreciated, using a logarithmic representation, such as the sound pressure level of the transfer function in the different frequency bands, a ratio may be determined as a difference.

[0060] As further illustrated in figure 2a, a processing block 136 of the spectral shape analysis stage 130 of the control device 100 is configured to determine based on the first ratio computed by the processing block 134 and the second ratio computed by the processing block 132 whether the measured transfer function meets one or more quality criteria, i.e. requirements. In an embodiment, these one or more quality criteria comprise: (a) that the first ratio is larger than the second ratio; (b) the first ratio is between 8 and 16 dB; and / or (c) the second ratio is larger than 0 dB. As will be appreciated, using relative differences between different frequency bands avoids defining absolute target functions and provides robust analysis of the spectral shape of the measurement result.

[0061] In the embodiment shown in figure lathe low frequency leakage analysis stage 140 (which is illustrated in more detail in figure 2b) of the control device 100 takes as input the low (Band 1), and mid (Band 2) frequency band portion of the measured acoustic response, i.e. transfer function. As in the case of the spectral shape analysis stage 130 described above, the low frequency leakage analysis stage 140 is configured to determine a measure of sound intensity (or magnitude or sound pressure level) of the acoustic response, i.e. transfer function, for instance, by forming an average (or sum) over the frequency coefficients in the respective frequency band. Furthermore, as illustrated in figure 2b, a processing block 142 of the low frequency leakage analysis stage 140 of the control device 100 is configured to determine a ratio (or equivalently a logarithmic difference) between, for instance, the sound intensity of the transfer function in the mid (Band 2) frequency band portion and the sound intensity of the transfer function in the low (Band 1 ) frequency band portion.

[0062] As further illustrated in figure 2b, a processing block 144 of the low frequency leakage analysis stage 140 of the control device 100 is configured to determine based on the ratio computed by the processing block 142 whether the measured transfer function meets one or more quality criteria, i.e. requirements. In an embodiment, these one or more quality criteria comprise: (a) that the ratio (i.e. logarithmic difference) is about 0 dB; and / or that the absolute value of the ratio (i.e. logarithmic difference) is smaller than 4.5 dB. As will be appreciated, because the decision implemented by the processing block 144 of the low frequency leakage analysis stage 140 is based on a relative comparison between mid and low frequency intensities, an absolute target definition may be avoided. Thus, a robust scheme for detecting low frequency measurements errors is provided which is independent of individual variations of the ear canal acoustics and robust to additive noise.

[0063] In the embodiment shown in figure la the spectral flatness analysis stage 120 (which is illustrated in more detail in figure 2c) of the control device 100 takes as input the low-mid (Band 4) frequency band portion of the measured acoustic response, i.e. transfer function and is configured to analyse the spectral variation within this low-mid band. To this end, a processing block 122 of the spectral flatness analysis stage 120 is configured to determine a spectral variability measure, for instance, a standard deviation of the intensities of the frequency coefficients of the transfer function in the low-mid frequency band. As further illustrated in figure 2c, a processing block 124 of the spectra flatness analysis stage 120 is configured to determine based on the spectral variability measure computed by the processing block 122 whether the measured transfer function meets one or more quality criteria, i.e. requirements. In an embodiment, these one or more quality criteria comprise whether the spectral variability measure, e.g. standard deviation, is smaller than a predefined threshold, in particular smaller than 3 dB. As will be appreciated, using spectral variability as a condition allows detecting self noises and structural noises caused by the userwearing the earphones 160. Opposed to typical noises which feature low spectral variability such as white noise, such noises are characterised by large spectral variability. Therefore, the defined threshold provides an effective means to detect such kind of noises and therefore increases the robustness.

[0064] As illustrated in figure la, a quality decision stage 150 of the control device 100 may aggregate the results, i.e. decisions provided by the spectral flatness analysis stage 120, the spectral shape analysis stage 130, and the low frequency leakage analysis stage 140 and make the final decision whether the transfer function meets one more quality criteria. In an embodiment, the final decision made by the quality decision stage 150, whether the measured transfer function is of good quality or not, may depend on any subset of the conditions, i.e. results provided by the stages 120, 130, 140 and may depend on different use cases. As will be appreciated, by combining several threshold based on different statistical properties of the measured acoustic response, a robust decision may be made. It is possible to reliably detect several different measurement errors, such as loose fitting, noise, and interferences.

[0065] Figure 3 shows a diagram illustrating two different transfer functions obtained by a set of earphones 160 according to an embodiment. The low leakage transfer function indicates a high quality result. The high leakage transfer function indicates a typically result obtained when the earphones have a loose fitting. The obvious loss in low frequency response and characteristic boost in mid frequencies between the sound intensity of the transfer function in the mid frequency band portion and the sound intensity of the transfer function in the low frequency band portion is well illustrated in figure 3.

[0066] Figures 4a-c show diagrams illustrating a plurality of different transfer functions obtained by a set of earphones 160 according to an embodiment. The dashed lines show a desired high quality transfer function (meeting the quality criteria), while the solid lines show for different types of interferences obtained in the same ear canal transfer functions which are not meeting the quality criteria.

[0067] Figure 4a illustrates an example of a strong interference in low frequency which is caused by a self noise of the user swallowing during the measurement of the transfer function. Characteristic interferences in the low and mid frequencies are obvious. Figure 4b indicates the obvious loss in low frequency response and characteristic boost in mid frequencies which results from a loose fitting earphone. Figure 4c illustrates an example of a strong interference caused by the user of the earphone talking during the measurement of the transfer function. All these different cases of transfer functions can be detected by the different quality criteria and the final decision made by the quality decision stage 150 of the control device 100 according to an embodiment provides an effective means to detect such kind of noises and therefore increases the robustness of the acoustic measurements in the ear canal.

[0068] The control device 100 described above may be used for obtaining robust acoustic measurements in the ear canal in different scenarios, such as for static measurements or adaptive measurements. Figure 5a shows a flow diagram illustrating processing steps implemented by the control device 100 according to an embodiment for a one-time measurement, for instance, for performing a calibration of the earphones 160. In an embodiment, at least some of the steps illustrated in figure 5a may be performed using a user interface for guiding the user, i.e. the wearer of the earphones 160.

[0069] In step 501 of figure 5a, a measurement of the acoustic response, i.e. transfer function of the earphone 160 inside the ear canal of a listener, i.e. the wearer of the earphone 160 is obtained by the control device 100.

[0070] In step 502 of figure 5a, the control device 100 is configured to analyse the acoustic response and determine a first quality measure of the acoustic response, i.e. a first ratio of the acoustic response.In step 503 of figure 5a, the control device 100 is configured to check whether the first quality measure, i.e. the first ratio of the response meets one or more quality requirements. If this is not the case, the control device 100 is configured in step 504 of figure 5a to notify the user, i.e. the wearer of the set of earphones 160 to avoid interferences, when the response is measured once more in step 501 of figure 5a.

[0071] If the first quality measure of the response, i.e. the first ratio determined in step 503 of figure 5a meets the one or more quality requirements, the control device 100 is configured in step 505 of figure 5a to analyse the acoustic response and determine a second quality measure of the response, i.e. a second ratio of the response.

[0072] In step 506 of figure 5a, the control device 100 is configured to check whether the second quality measure, i.e. the second ratio of the response meets one or more quality requirements. If this is not the case, the control device 100 is configured in step 508 of figure 5a to notify the user, i.e. the wearer of the set of earphones 160 to ensure a better fit of the set of earphones 160, when the response is measured once more in step 501 of figure 5a.

[0073] If the second quality measure of the response, i.e. the second ratio determined in step 505 of figure 5a meets the one or more quality requirements, the control device 100 is configured in step 507 of figure 5a to allow further use of the acoustic response, such as for adapting an audio signal to be rendered by the set of earphones or for identifying the wearer of the set earphones.

[0074] Figure 5a shows a flow diagram illustrating processing steps implemented by the control device 100 according to an embodiment for measurements of the acoustic response, i.e. transfer function in an adaptive manner without any user interaction. In an embodiment, the control device 100 may be configured to perform the steps illustrated in figure 5b continuously or periodically.

[0075] In step 511 of figure 5b, the control device 100 is configured to analyse the frequency content of an audio signal being currently played over the set of earphones 160.

[0076] In step 512 of figure 5b, the control device 100 is configured to check whether the current frequency content of the audio signal played by the set of earphones 160 meets one or more requirements. If this is not the case, i.e. if the current frequency content of the audio signal does not meet the one or more requirements, the control device 100 waits for a pre-defined amount of time, such as 10 seconds, in step 512a of figure 5b before returning to step 511 of figure 5b.

[0077] If the current frequency content of the audio signal meets the one or more requirements, the control device 100 is configured in step 513 of figure 5b to obtain a measurement of the acoustic response, i.e. transfer function of the earphone 160 inside the ear canal of a listener, i.e. the wearer of the earphone 160.

[0078] In step 514 of figure 5b, the control device 100 is configured to analyse the acoustic response and determine a first quality measure of the acoustic response, i.e. a first ratio of the acoustic response.

[0079] In step 515 of figure 5b, the control device 100 is configured to check whether the first quality measure, i.e. the first ratio of the response meets one or more quality requirements. If this is not the case, the control device 100 is configured in step 515a of figure 5b to wait for a pre-defined amount of time, such as 10 seconds, before returning to step 511 of figure 5b.

[0080] If the first quality measure of the response, i.e. the first ratio determined in step 514 of figure 5b meets the one or more quality requirements, the control device 100 is configured in step 516 of figure 5b to analyse the acoustic response and determine a second quality measure of the response, i.e. a second ratio of the response.In step 517 of figure 5b, the control device 100 is configured to check whether the second quality measure, i.e. the second ratio of the response meets one or more quality requirements. If this is not the case, the control device 100 is configured in step 512a of figure 5b to wait for a pre-defined amount of time, such as 10 seconds, before returning to step 511 of figure 5b.

[0081] If the second quality measure of the response, i.e. the second ratio determined in step 516 of figure 5b meets the one or more quality requirements, the control device 100 is configured in step 518 of figure 5b to allow further use of the acoustic response, such as for adapting the audio signal currently rendered by the set of earphones 160.

[0082] Figure 6 shows a flow diagram illustrating a method 600 for controlling a set of earphones, including, for instance, the earphone 160 illustrated in figure lb. The method 600 comprises a step 601 of determining a transfer function between the loudspeaker 162 of the earphone 160 of the set of earphones and the microphone 164 of the earphone 160. Moreover, the method 600 comprises a step 603 of determining a plurality of ratios of the transfer function in a plurality of frequency bands. The method 600 comprises further a step 605 of determining, based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets one or more quality criteria. As already described above, if this is the case, i.e. in case the transfer function meets the one or more quality criteria, the transfer function may be used for adapting an audio signal to be rendered by the set of earphones or for identifying the wearer of the set earphones.

[0083] Embodiments of the control device 100 disclosed herein provide an approach which can deal with the different variations of influences affecting acoustic measurements in the ear canal. More specifically, embodiments of the control device 100 disclosed herein allow to deal with the individual variations of the ear canal shape and the insertion depth which adds resonances and can create strong variations of the measured responses and make a definition of a fixed (absolute) target curve only applicable to low frequencies but not to the entire spectrum. Moreover, embodiments of the control device 100 disclosed herein allow to deal with the following variations and / or interferences: air conducted noises (depending on the environment of the user, the noise level is affecting the measurement result); bone conducted noises (jaw, teeth and head movements from the user result in strong bone-conducted noise interferences in the microphone 164 embedded in the earphone 160); self-noise of the user such as caused by talking or coughing which is an additive component; structure-bome sound interferences which can be caused e.g. , when the user touches the earphone 160 during the measurement; the ear canal being a dynamic environment where factors such as movement, changes in pressure, and the presence of earwax can influence acoustic measurements; and / or unpredictable behaviour of the user which can add strong air-conducted noise, bone-conducted interferences or other noises resulting from the activity of the user.

[0084] The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

[0085] In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

[0086] In addition, functional units in the embodiments of the invention may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

Claims

CLAIMS1. A control device (100) for controlling a set of earphones, wherein the control device (100) is configured: determine a transfer function between a loudspeaker (162) of an earphone (160) of the set of earphones and a microphone (164) of the earphone (160);determine a plurality of ratios of the transfer function in a plurality of frequency bands; anddetermine, based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets one or more quality criteria.

2. The control device (100) of claim 1, wherein the control device (100) is configured to determine, based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets one or more quality criteria, for determining whether the transfer function is of sufficient quality for adjusting an audio signal to be rendered by the earphone (160) and / or for identifying a wearer of the set of earphones.

3. The control device (100) of claim 1 or 2, wherein the control device (100) is configured to determine the transfer function based on an in-vivo measurement of an acoustic response.

4. The control device (100) of claim 3, wherein the control device (1009 is configured to continuously or periodically determine the transfer function based on an in-vivo measurement of an acoustic response to an audio signal rendered by the earphone (160) and to continuously or periodically adjust the audio signal rendered by the earphone (160) based on the transfer function, if the transfer function meets one or more quality criteria for adjusting the audio signal rendered by the earphone (160).

5. The control device (100) of any one of the preceding claims, wherein the control device (100) is configured to signal to a wearer of the set of earphones to adjust the fitting of the set of earphones and / or to avoid interferences, if the transfer function does not meet the one or more quality criteria.

6. The control device (100) of any one of the preceding claims, wherein, if the transfer function does not meet the one or more quality criteria, the control device (100) is configured to:determine a further transfer function between the loudspeaker (162) of the earphone (160) of the set of earphones and the microphone (164) of the earphone (160);determine a plurality of further ratios of the further transfer function in the plurality of frequency bands; and determine, based on the plurality of further ratios of the further transfer function in the plurality of frequency bands, whether the further transfer function meets the one or more quality criteria.

7. The control device (100) of any one of the preceding claims, wherein the control device (100) is configured to determine, based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets the one or more quality criteria by comparing the plurality of ratios with a plurality of ratio thresholds.

8. The control device (100) of claim 7, wherein the plurality of ratios of the transfer function in the plurality of frequency bands comprises a first ratio between the transfer function in a high frequency band and the transfer function in a mid frequency band and a second ratio between the transfer function in the high frequency band and the transfer function in a low frequency band.

9. The control device (100) of claim 8, wherein the control device (100) is configured to determine whether the first ratio is larger than the second ratio for determining whether the transfer function meets the one or more quality criteria.

10. The control device (100) of any one of the preceding claims, wherein the control device (100) is further configured to determine a standard deviation of the transfer function in at least one of the plurality of frequency bands and to determine, based on the plurality of ratios of the transfer function in the plurality of frequency bands and based on the standard deviation of the transfer function in the at least one of the plurality of frequency bands, whether the transfer function meets the one or more quality criteria.

11. The control device (100) of any one of the preceding claims, wherein the plurality of frequency bands comprises a low frequency band, a mid frequency band, a high frequency band, and / or a low-mid frequency band.

12. The control device (100) of any one of the preceding claims, wherein the control device (100) is a smartphone, smartwatch, or audio player.

13. A set of earphones, wherein at least one earphone (160) of the set of earphones comprises a control device (100) according to any one of the preceding claims.

14. An audio assembly, comprising:a set of earphones; anda control device (100) according to any one of claims 1 to 12.

15. A method (600) for controlling a set of earphones, wherein the method (600) comprises:determining (601) a transfer function between a loudspeaker (162) of an earphone (160) of the set of earphones and a microphone (164) of the earphone (160);determining (603) a plurality of ratios of the transfer function in a plurality of frequency bands; anddetermining (605), based on the plurality of ratios of the transfer function in the plurality of frequency bands, whether the transfer function meets one or more quality criteria.

16. A computer program product comprising a computer-readable storage medium for storing program code which causes a computer or a processor to perform the method (600) of claim 15 when the program code is executed by the computer or the processor.

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