AUDIO SYSTEM AND SIGNAL PROCESSING METHOD FOR AN EAR MOUNTABLE PLAYBACK DEVICE

Abstract

An audio system for an ear mountable playback device comprises a speaker and an error microphone that is configured to sense sound being output from the speaker and ambient sound. The audio system further comprises a detection engine that is configured to determine a driver response between the speaker and the error microphone, and to estimate a leakage condition from the determined driver response.

Claims

1. An audio system for an ear mountable playback device comprising a speaker; an error microphone configured to sense sound being output from the speaker and ambient sound; and a detection engine configured to determine a driver response between the speaker and the error microphone; and estimate a leakage condition from the determined driver response.

2. The audio system according to claim 1, wherein determining the driver response comprises measuring a property of a first signal that is applied to the speaker; measuring a property of a second signal that is detected by the error microphone; and calculating the driver response from the first and the second property.

3. The audio system according to claim 2, wherein the property of the first and the second signal is an amplitude of the respective signal.

4. The audio system according to claim 2, wherein for calculating the driver response, the first and the second signal are bandpass filtered with a predetermined bandpass frequency range.

5. The audio system according to claim 2, wherein the driver response is calculated as a ratio of energy levels of the first and the second signal.

6. The audio systems according to claim 2, wherein the driver response is calculated from response values determined at predetermined frequencies or frequency ranges of the first and the second signal, respectively.

7. The audio system according to claim 2, wherein the driver response is calculated by applying to the first and the second signal a process which differentiates energy into at least two frequency bands, such as a frequency transformation.

8. The audio system according to claim 7, wherein calculating the driver response further comprises determining a first value from applying the process to the first signal; determining a second value from applying the process to the second signal, and comparing the first value to the second value.

9. The audio system according to claim 8, wherein the first and the second value are determined for predetermined frequencies or frequency ranges after applying the process to the first and the second signal.

10. The audio system according to claim 1, wherein estimating the leakage condition comprises determining a leakage value from the determined driver response.

11. The audio system according to claim 10, wherein the leakage value is determined by comparing the determined driver response with reference values in a lookup table.

12. The audio system according to claim 1, wherein the audio system further comprises a further microphone and the leakage condition is used to adjust a feedforward filter and/or a feedback filter and/or a compensation filter of the audio system.

13. The audio system according to claim 1, wherein the leakage condition is estimated when a ratio of a wanted signal to a disturbance signal.

14. The audio system according to claim 1, wherein the driver response is determined without adapting and monitoring a filter that matches the driver response.

15. An ear mountable playback device comprising an audio system according to claim 1.

16. A signal processing method for an ear mountable playback device comprising a speaker and an error microphone that senses sound being output from the speaker and ambient sound, the method comprising generating by means of the error microphone an error signal; determining from the error signal and from a signal applied to the speaker a driver response; and estimating a leakage condition from the determined driver response.

17. The audio system according to claim 1, wherein the leakage condition is estimated when a ratio of a wanted signal to an ambient noise signal is larger than a threshold.

18. The audio system according to claim 1, wherein the detection engine is configured to determine the driver response from a first signal that is applied to the speaker and a second signal that is detected from the error microphone; and estimate the leakage condition by comparing the determined driver response to known driver responses at different leakage conditions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The improved concept will be described in more detail in the following with the aid of drawings. Elements having the same or similar function bear the same reference symbols throughout the drawings. Hence their description is not necessarily repeated in the description to the following drawings.

[0056] In the drawings:

[0057] FIG. 1 shows a schematic view of a headphone;

[0058] FIG. 2 shows a block diagram of a generic adaptive ANC system;

[0059] FIG. 3 shows an example representation of a “leaky” type earphone;

[0060] FIG. 4 shows an example headphone worn by a user with several sound paths from an ambient sound source;

[0061] FIG. 5 shows an example representation of an ANC enabled handset;

[0062] FIG. 6 shows a block diagram of an exemplary embodiment of an audio system for an ear mountable playback device according to the improved concept; and

[0063] FIG. 7 shows a signal diagram displaying the frequency dependent driver responses for different acoustic leakage conditions.

DETAILED DESCRIPTION

[0064] FIG. 1 shows a schematic view of an ANC enabled playback device in form of a headphone HP that in this example is designed as an over-ear or circumaural headphone. Only a portion of the headphone HP is shown, corresponding to a single audio channel. However, extension to a stereo headphone will be apparent to the skilled reader. The headphone HP comprises a housing HS carrying a speaker SP, a feedback noise microphone or error microphone FB_MIC and optionally an ambient noise microphone or feedforward microphone FF_MIC. The error microphone FB_MIC is particularly directed or arranged such that it records both ambient noise and sound played over the speaker SP. Optionally, the error microphone FB_MIC is arranged in close proximity to the speaker, for example close to an edge of the speaker SP or to the speaker's membrane. Alternatively, the error microphone FB_MIC may be arranged close to the ear canal of the user of the headphone HP. The optional ambient noise/feedforward microphone FF_MIC is particularly directed or arranged such that it mainly records ambient noise from outside the headphone HP.

[0065] Depending on the type of ANC to be performed, the optional ambient noise microphone FF_MIC may be omitted, if only feedback ANC is performed. The error microphone FB_MIC may be used according to the improved concept to provide an error signal being the basis for a determination of the wearing condition, respectively leakage condition, of the headphone HP, when the headphone HP is worn by a user.

[0066] In the embodiment of FIG. 1, a detection engine DET is located within the headphone HP for performing various kinds of signal processing operations, examples of which will be described within the disclosure below. The detection engine DET may also be placed outside the headphone HP, e.g. in an external device located in a mobile handset or phone or within a cable of the headphone HP.

[0067] FIG. 2 shows a block diagram of a generic adaptive ANC system. The system comprises the error microphone FB_MIC and the feedforward microphone FF_MIC, both providing their output signals to an adaptation engine ADP. The noise signal recorded with the feedforward microphone FF_MIC is further provided to a feedforward filter F for generating an anti-noise signal being output via the speaker SP. At the error microphone FB_MIC, the sound being output from the speaker SP combines with ambient noise and is recorded as an error signal that includes the remaining portion of the ambient noise after ANC. This error signal is used by the sound adaptation engine ADP for adjusting a filter response of the feedforward filter.

[0068] FIG. 3 shows an example representation of a “leaky” type earphone, i.e. an earphone featuring some leakage between the ambient environment and the ear canal EC. In particular, a sound path between the ambient environment and the ear canal EC exists, denoted as “acoustic leakage” in the drawing.

[0069] FIG. 4 shows an example configuration of a headphone HP worn by a user with several sound paths. The headphone HP shown in FIG. 4 stands as an example for any ear mountable playback device of a noise cancellation enabled audio system and can e.g. include in-ear headphones or earphones, on-ear headphones or over-ear headphones. Instead of a headphone, the ear mountable playback device could also be a mobile phone or a similar device.

[0070] The headphone HP in this example features a loudspeaker SP, a feedback noise microphone FB_MIC and, optionally, an ambient noise microphone FF_MIC, which e.g. is designed as a feedforward noise cancellation microphone. Internal processing details of the headphone HP are not shown here for reasons of a better overview.

[0071] In the configuration shown in FIG. 4, several sound paths exist, of which each can be represented by a respective acoustic response function or acoustic transfer function. For example, a first acoustic transfer function DFBM represents a sound path between the speaker SP and the feedback noise microphone FB_MIC, and may be called a driver-to-feedback response function. The first acoustic transfer function DFBM may include the response of the speaker SP itself. A second acoustic transfer function DE represents the acoustic sound path between the headphone's speaker SP, potentially including the response of the speaker SP itself, and a user's eardrum ED being exposed to the speaker SP, and may be called a driver-to-ear response function. A third acoustic transfer function AE represents the acoustic sound path between the ambient sound source and the eardrum ED through the user's ear canal EC, and may be called an ambient-to-ear response function. A fourth acoustic transfer function AFBM represents the acoustic sound path between the ambient sound source and the feedback noise microphone FB_MIC, and may be called an ambient-to-feedback response function. The driver response that is subject to this disclosure results from the first acoustic transfer function DFBM, i.e. the ratio of the total sound signal detected by the error microphone FB_MIC to the total signal driving the speaker SP.

[0072] If the ambient noise microphone FF_MIC is present, a fifth acoustic transfer function AFFM represents the acoustic sound path between the ambient sound source and the ambient noise microphone FF_MIC, and may be called an ambient-to-feedforward microphone response function.

[0073] Response functions or transfer functions of the headphone HP, in particular between the microphones FB_MIC and FF_MIC and the speaker SP, can be used with a feedback filter function B and feedforward filter function F, which may be parameterized as noise cancellation filters during operation.

[0074] The headphone HP as an example of the ear-mountable playback device may be embodied with both the microphones FB_MIC and FF_MIC being active or enabled such that hybrid ANC can be performed, or as a FB ANC device, where only the feedback noise microphone FB_MIC is active and an ambient noise microphone FF_MIC is not present or at least not active. Hence, in the following, if signals or acoustic transfer functions are used that refer to the ambient noise microphone FF_MIC, this microphone is to be assumed as present, while it is otherwise assumed to be optional.

[0075] Any processing of the microphone signals or any signal transmission are left out in FIG. 4 for reasons of a better overview. However, processing of the microphone signals in order to perform ANC may be implemented in a processor located within the headphone or other ear-mountable playback device or externally from the headphone in a dedicated processing unit. The processor or processing unit may be called an adaptation engine. If the processing unit is integrated into the playback device, the playback device itself may form a noise cancellation enabled audio system. If processing is performed externally, the external device or processor together with the playback device may form the noise cancellation enabled audio system. For example, processing may be performed in a mobile device like a mobile phone or a mobile audio player, to which the headphone is connected with or without wires.

[0076] In the various embodiments, the FB or error microphone FB_MIC may be located in a dedicated cavity, as for example detailed in ams application EP17208972.4.

[0077] Referring now to FIG. 5, another example of a noise cancellation enabled audio system is presented. In this example implementation, the system is formed by a mobile device like a mobile phone MP that includes the playback device with speaker SP, feedback or error microphone FB_MIC, ambient noise or feedforward microphone FF_MIC and an adaptation engine ADP for performing inter alia ANC and/or other signal processing during operation.

[0078] In a further implementation, not shown, a headphone HP, e.g. like that shown in FIG. 1 or FIG. 4, can be connected to the mobile phone MP wherein signals from the microphones FB_MIC, FF_MIC are transmitted from the headphone to the mobile phone MP, in particular the mobile phone's processor PROC for generating the audio signal to be played over the headphone's speaker. For example, depending on whether the headphone is connected to the mobile phone or not, ANC is performed with the internal components, i.e. speaker and microphones, of the mobile phone or with the speaker and microphones of the headphone, thereby using different sets of filter parameters in each case.

[0079] In the following, several implementations of the improved concept will be described in conjunction with a specific use case. It should however be apparent to the skilled person that details described for the implementation may still be applied to other implementations.

[0080] FIG. 6 shows a block diagram of a hybrid ANC audio system according to the improved concept. The system comprises the error microphone FB_MIC and the feedforward microphone FF_MIC. The noise signal recorded with the feedforward microphone FF_MIC is provided to a feedforward type first noise filter F for generating an anti-noise signal being output via the speaker SP together with a wanted signal, e.g. music. At the error microphone FB_MIC, the sound being output from the speaker SP combines with ambient noise and is recorded as an error signal that includes the remaining portion of the ambient noise after ANC. This error signal is output to a feedback type second noise filter B for generating a further anti-noise signal being summed to the anti-noise signal and the wanted signal and also output via the speaker SP.

[0081] The total signal applied to the speaker SP and the error signal from the error microphone FB_MIC are further provided to the detection engine DET for determining the driver response and a subsequent estimation of the leakage condition. For example, the driver response is calculated from the two signals and subsequently evaluated and compared to known driver responses at different leakage conditions, e.g. stored in a lookup table, in order to determine a leakage value quantifying the actual leakage condition of the earphone. Consequently, the leakage value is used by the adaptation engine ADP to adjust a filter response of the feedforward filter F and/or the of the feedback filter B.

[0082] The hybrid system in this implementation further comprises an optional music compensation filter C as detailed in ams patent U.S. Pat. No. 9,779,718 B2. The wanted signal, e.g. music, in this case is provided to the music compensation filter C in order to compensate for the wanted signal being attenuated by the feedback noise cancellation, for instance.

[0083] FIG. 7 shows a signal diagram displaying the amplitude of the frequency dependent driver responses for different acoustic leakage conditions. For example, the marked low leak driver response corresponds to no leak, i.e. an on-ear state with no or insignificant acoustic leakage between the ear canal and the ambient environment, and the marked high leak driver response corresponds to a maximum, i.e. a state with a large acoustic leakage between the ear canal and the ambient environment. An intermediate leakage condition then results in a driver response amplitude in between aforementioned high and low leak conditions, indicated as three exemplary driver responses in the FIG. 7. For example, the typical range of possible amplitudes for the driver response between minimum and maximum is in the order of 30 dB, which again may be highly frequency dependent. For example, the driver response shows a significant, i.e. the largest, leakage dependence at low frequencies. Hence, the detection engine may be configured to only evaluate the signal applied to the speaker SP and the error signal from the error microphone FB_MIC in this frequency range, e.g. between 10 Hz and 200 Hz. This can be realized via bandpass filtering or via fast Fourier transformation of said signals, for example.

[0084] The detection engine DET may be configured to evaluate the determined driver response and to compare it to the predetermined minimum and maximum driver responses at a frequency range or at several distinct frequencies. From this, a leakage value quantifying the leakage condition may be determined, for example as a normalized value between 0 and 1, with 0 indicating the minimum and 1 corresponding to the maximum leakage condition.