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, an error microphone configured to predominantly sense sound being output from the speaker and a further microphone configured to predominantly sense ambient sound. The system further comprises a first noise filter coupling the further microphone to the speaker, a second noise filter coupling the error microphone to the speaker and an adaptation engine. The adaptation engine is configured to adapt a response of the first noise filter depending on error signals from at least the error microphone, estimate a leakage condition from the response of the first noise filter, and adapt a response of the second noise filter depending on the estimated leakage condition.

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; a further microphone configured to predominantly sense ambient sound; a first noise filter coupling the further microphone to the speaker; a second noise filter coupling the error microphone to the speaker; and an adaptation engine configured to adapt a response of the first noise filter depending on error signals from at least the error microphone; estimate a leakage condition from the response of the first noise filter; and adapt a response of the second noise filter depending on the estimated leakage condition.

2. The audio system according to claim 1, wherein the adaptation engine is configured to estimate the leakage condition by comparing the adapted response of the first noise filter to a predetermined minimum and/or maximum response.

3. The audio system according to claim 2, wherein comparing the adapted response of the first noise filter to the predetermined minimum and/or maximum response is performed in the frequency domain.

4. The audio system according to claim 1, wherein the adaptation engine is configured to estimate the leakage condition at one or more distinct frequencies or frequency ranges.

5. The audio system according to claim 1, wherein the adaptation engine is configured to estimate the leakage condition by determining a leakage value.

6. The audio system according to claim 5, wherein the adaptation engine is further configured to estimate the leakage condition by estimating at each of a set of distinct frequencies or frequency ranges an interim leakage value based on an amplitude value of the response of the first noise filter within a range that is defined by predetermined minimum and maximum responses at the respective distinct frequency or frequency range; and calculating the leakage value from the interim leakage values.

7. (canceled)

8. The audio system according to claim 1, wherein the adaptation engine is configured to adapt the response of the second noise filter by setting one of a set of predefined filters as the second noise filter.

9. (canceled)

10. (canceled)

11. (canceled)

12. (canceled)

13. (canceled)

14. The audio system according to claim 1, further comprising a combiner configured to generate the response of the second noise filter based on a combination of an output of a first interpolation filter amplified with a first adjustable gain factor and an output of a second interpolation filter amplified with a second adjustable gain factor; and wherein the adaptation engine is further configured to adapt the response of the second noise filter by adjusting at least one of the first and the second adjustable gain factors.

15. (canceled)

16. The audio system according to claim 1, which is configured to perform noise cancellation.

17. (canceled)

18. The audio system according to claim 1, wherein the further microphone is a feedforward error microphone and the first noise filter is of a feedforward noise cancellation type; and the error microphone is a feedback error microphone and the second noise filter is of a feedback noise cancellation type.

19. The audio system according to claim 1, wherein the adaptation engine is further configured to compare a signal level of the further microphone to a signal level of the error microphone; and based on the comparison of the signal levels evaluate an accuracy of the estimated leakage condition.

20. The audio system according to claim 19, wherein the adaptation engine is further configured to activate and deactivate the second noise filter depending on the accuracy of the estimated leakage condition.

21. The audio system according to claim 1 wherein the leakage condition characterizes a leak between an ambient of the audio system and a volume which is defined by an ear canal of a user and a cavity of the audio system, wherein the cavity is arranged at a preferential side for sound emission of the speaker.

22. The audio system according to claim 1, further comprising a proximity sensor configured to detect a proximity between the audio system and an ear canal of a user; wherein the adaptation engine is further configured to estimate the leakage condition from the response of the first noise filter and the proximity.

23. The audio system according to claim 1, which includes the playback device.

24. (canceled)

25. The audio system according to claim 1, wherein the playback device is a headphone or an earphone.

26. The audio system according to claim 1, wherein the adaptation engine is configured to adapt the response of the second noise filter such that a stable operation of the response of the second noise filter is maintained.

27. The audio system according to claim 1, wherein the further microphone detects a negligible level of the sound output from the speaker.

28. The audio system according to claim 1, wherein the error microphone detects a negligible level of the ambient sound.

29. A signal processing method for an ear mountable playback device comprising a speaker, an error microphone that predominantly senses sound being output from the speaker, and a further microphone that predominantly senses ambient sound, the method comprising generating by means of the error microphone an error signal; adapting a response of a first noise filter coupled between the further microphone and the speaker depending on at least the error signal; estimating a leakage condition from the response of the first noise filter; and adapting a response of a second noise filter coupled between the error microphone and the speaker depending on the leakage condition.

30. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] 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 numerals throughout the drawings. Hence their description is not necessarily repeated in following drawings.

[0072] In the drawings:

[0073] FIG. 1 shows a schematic view of a headphone;

[0074] FIG. 2 shows a block diagram of a generic adaptive ANC system;

[0075] FIG. 3 shows an example representation of a “leaky” type earphone;

[0076] FIG. 4 shows an example headphone worn by a user with several sound paths from an ambient sound source;

[0077] FIG. 5 shows an example representation of an ANC enabled handset;

[0078] FIG. 6 shows a block diagram of an adaptive hybrid ANC system according to the improved concept; and

[0079] FIG. 7 shows a signal diagram displaying the amplitude responses of an adapted noise filter.

DETAILED DESCRIPTION

[0080] 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 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. Preferably 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. The ambient noise/feedforward microphone FF_MIC is particularly directed or arranged such that it mainly records ambient noise from outside the headphone HP.

[0081] Depending on the type of ANC to be performed, the 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.

[0082] In the embodiment of FIG. 1, an adaptation engine ADP 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 adaptation engine ADP 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.

[0083] 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 the adaptation engine ADP. The noise signal recorded with the feedforward microphone FF_MIC is further provided to a feedforward filter FNF 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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 response function.

[0089] 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 FNF, which may be parameterized as noise cancellation filters during operation.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] In the following, several implementations of the improved concept will be described in conjunction with specific use cases. It should however be apparent to the skilled person that details described for one implementation may still be applied to one or more of the other implementations.

[0096] FIG. 6 shows a block diagram of an adaptive hybrid ANC system according to the improved concept. The system comprises the error microphone FB_MIC and the feedforward microphone FF_MIC, both providing their output signals to the adaptation engine ADP. The noise signal recorded with the feedforward microphone FF_MIC is further provided to a feedforward type first noise filter FNF 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 output to a feedback type second noise filter SNF for generating a further anti-noise signal being summed to the anti-noise signal and also output via the speaker SP. The error signal is further provided to the sound adaptation engine ADP for adjusting a filter response of the feedforward filter FNF.

[0097] Furthermore, the adjusting of the feedforward filter FNF is further used to determine a leakage condition. For example, a response of the feedforward filter FNF is evaluated and compared to a known leakage condition in order to determine a leakage value quantifying the leakage condition of the earphone. Consequently, the leakage value is used by the adaptation engine ADP to adjust a filter response of the feedback filter SNF.

[0098] FIG. 7 shows a signal diagram displaying the amplitude of the response of an adapted FF filter together with a predetermined or precalculated low leak, i.e. minimum, and high leak, i.e. maximum, filter response in dependence of frequency. For example, the low leak FF filter response corresponds to no leak, i.e. an on-ear state with no acoustic leakage between the ear canal and the ambient environment, and the high leak FF filter response corresponds to a maximum, i.e. a state with a large acoustic leakage between the ear canal and the ambient environment. An adaptation of the FF filter for intermediate leakage condition then results in a filter response in between these two predetermined responses, as shown for an exemplary response of an adapted FF filter. For example, the typical range of possible amplitudes for the FF filter response between minimum and maximum is in the order of 15 dB.

[0099] The adaptation engine ADP may be configured to evaluate the response of the adapted FF filter and to compare it to the predetermined minimum and maximum responses at three distinct frequencies that are marked as the bold vertical lines in FIG. 8. In this example, the adapted FF filter is closer to the low leak response, indicating a leakage condition that is slightly above the minimum. From this, a leakage value quantifying the leakage condition may be determined, for example as a value between 0 and 1, with 0 indicating the minimum and 1 corresponding to the maximum leakage condition.

[0100] Moreover, the adaptation engine ADP may be configured to detect and evaluate a ratio of the energy at the FB microphone FB_MIC relative to the energy at the FF microphone FF_MIC, and to determine an accuracy of the estimated leakage value from this ratio. Typical error margins of the leakage value are in the order of 5%, which constitutes sufficient accuracy for setting an FB filter based on the leakage value. If the leakage value's accuracy is below a certain threshold, the adaptation engine ADP may be configured to suspend the FB ANC, for example.