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

Abstract

An audio system for an ear mountable playback device comprises a compensation filter configured to generate a third compensation signal by applying filter operations to an audio signal, and an error compensation unit configured to generate a compensated error signal on the basis of the third compensation signal and a disturbed audio signal from an error microphone. The audio system further comprises a first noise filter configured to be adapted based on the compensated error signal, and a detection unit configured to estimate the acoustic leakage condition on the basis of the first noise filter or of the disturbed audio signal and an audio output signal. The compensation filter is configured to be adapted based on the acoustic leakage condition.

Claims

1. An audio system for an ear mountable playback device comprising a speaker configured to generate a speaker signal on the basis of an audio output signal; an error microphone configured to generate a disturbed audio signal on the basis of ambient noise and the speaker signal; a further microphone configured to generate a noise signal on the basis of the ambient noise; a first noise filter configured to generate a first compensation signal by applying filter operations to the noise signal; and be adapted based on a compensated error signal; a first mixer configured to generate the audio output signal by superimposing an audio signal, the first compensation signal and a second compensation signal; a compensation filter configured to generate a third compensation signal by applying filter operations to the audio signal; and be adapted based on an acoustic leakage condition; a second noise filter configured to generate the second compensation signal by applying filter operations to an intermediate compensation signal that is generated by subtracting the third compensation signal from the disturbed audio signal; an error compensation unit configured to generate the compensated error signal on the basis of the disturbed audio signal and the third compensation signal; and a detection unit configured to estimate the acoustic leakage condition on the basis of the first noise filter or of the disturbed audio signal and the audio output signal.

2. The audio system according to claim 1, wherein the compensation filter is configured to match a leakage-dependent driver response between the speaker and the error microphone.

3. The audio system according to claim 1, wherein the error compensation unit comprises a second mixer configured to generate the compensated error signal by subtracting from the disturbed audio signal a removal signal that is based on the third compensation signal.

4. The audio system according to claim 3, wherein the error compensation unit further comprises a filter element configured to generate the removal signal from the third compensation signal.

5. The audio system according to claim 4, wherein for generating the removal signal, the filter element is configured to apply filter operations to the third compensation signal.

6. The audio system according to claim 4, wherein for generating the removal signal, the error compensation unit is configured to control an adjustable gain of the filter element depending on the third compensation signal and the compensated error signal.

7. The audio system according to claim 6, wherein the error compensation unit is configured to control the adjustable gain by means of a feedback loop.

8. The audio system according to claim 6, wherein the error compensation unit is configured to control the adjustable gain by applying an error minimization algorithm to the third compensation signal and the compensated error signal.

9. The audio system according to claim 1, wherein the second noise filter is further configured to be adapted based on the leakage condition.

10. The audio system according to claim 1, wherein the detection unit is configured to estimate the leakage condition on the basis of the disturbed audio signal and the audio output signal if a ratio between the speaker signal and the ambient noise exceeds a set threshold; and on the basis of the first noise filter otherwise.

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

12. The audio system according to claim 1, wherein estimating the leakage condition comprises determining a leakage value.

13. The audio system according to claim 1, wherein the compensation filter is adapted on the basis of a comparison of the leakage condition with reference leakage conditions in a lookup table.

14. The audio system according to claim 1, wherein for generating the compensated error signal (EM), an adjustable gain is applied to the third compensation signal (CS3); and for generating the intermediate compensation signal, the adjustable gain is not applied to the third compensation signal (CS3).

15. The audio system according to claim 1, wherein the detection unit (DET) is configured to estimate the acoustic leakage condition on the basis of the first noise filter (F) and on the basis of the disturbed audio signal (E) and the audio output signal.

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

17. A signal processing method for an ear mountable playback device with a speaker generating a speaker signal based on an audio output signal, with a further microphone configured to generate a noise signal on the basis of ambient noise, and with an error microphone configured to generate a disturbed audio signal on the basis of the speaker signal and the ambient noise, the method comprising generating a first compensation signal by applying filter operations of a first noise filter to the noise signal; generating the audio output signal by superimposing an audio signal, the first compensation signal and a second compensation signal; generating a third compensation signal by applying filter operations of a compensation filter to the audio signal; and generating the second compensation signal by applying filter operations of a second noise filter to an intermediate compensation signal that is generated by subtracting the third compensation signal from the disturbed audio signal; generating a compensated error signal based on the disturbed audio signal and the third compensation signal; estimating a leakage condition on the basis of the first noise filter or of the disturbed audio signal and the audio output signal; adapting the first noise filter based on the compensated error signal; and adapting the compensation filter based on the leakage condition.

18. The audio system according to claim 6, wherein the error compensation unit is configured to control the adjustable gain by applying a least mean squares algorithm to the third compensation signal and the compensated error signal.

19. The audio system according to claim 1, wherein the detection unit is configured to estimate the leakage condition on the basis of the disturbed audio signal and the audio output signal if a ratio between the speaker signal and the ambient noise exceeds a set threshold; and on the basis of filter parameters of the first noise filter otherwise.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] 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.

[0054] In the drawings:

[0055] FIG. 1 shows a schematic view of a headphone;

[0056] FIG. 2 shows a block diagram of a generic adaptive ANC system;

[0057] FIG. 3 shows an example representation of a “leaky” type earphone;

[0058] FIG. 4 shows an example headphone worn by a user with several sound paths from an ambient sound source;

[0059] FIG. 5 shows an example representation of an ANC enabled handset; and

[0060] 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.

DETAILED DESCRIPTION

[0061] 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. 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 ambient noise/feedforward microphone FF_MIC is particularly directed or arranged such that it mainly records ambient noise from outside the headphone HP.

[0062] 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 acoustic leakage condition, of the headphone HP, when the headphone HP is worn by a user.

[0063] In the embodiment of FIG. 1, an adaptation unit ADP that may comprise a detection unit DET, a tuning unit TU and/or an error compensation unit ECU according to the improved concept 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 tuning unit TU, the detection unit DET and the error compensation unit ECU may be arranged as a single unit or separately. They 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.

[0064] 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 unit 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 unit ADP for adjusting a filter response of the feedforward filter.

[0065] 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.

[0066] 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 AS 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.

[0067] 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.

[0068] 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 and the fourth acoustic transfer function AFBM, i.e. the total sound signal detected by the error microphone FB_MIC.

[0069] Concerning the ambient noise microphone FF_MIC, 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.

[0070] 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.

[0071] 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 unit. If the processing unit is integrated into the playback device, the playback device itself may form a noise cancellation enabled audio system AS. If processing is performed externally, the external device or processor together with the playback device may form the noise cancellation enabled audio system AS. 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.

[0072] 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.

[0073] Referring now to FIG. 5, another example of a noise cancellation enabled audio system AS 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 unit ADP for performing inter alia ANC and/or other signal processing during operation.

[0074] 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.

[0075] 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.

[0076] FIG. 6 shows a block diagram of a hybrid ANC audio system AS according to the improved concept. The audio system AS comprises the error microphone FB_MIC and the feedforward microphone FF_MIC. The noise signal N from the feedforward microphone FF_MIC is provided to a feedforward type first noise filter F for generating the first compensation signal CS1 as an anti-noise signal which is provided to the first mixer M1. At the error microphone FB_MIC, the speaker signal SPS combines with ambient noise NOISE and is recorded as a disturbed audio signal E that includes the remaining portion of the ambient noise after ANC.

[0077] The disturbed audio signal E is provided to the third mixer M3 which performs a music compensation process, i.e. subtracts the third compensation signal CS3 from said disturbed audio signal E and provides the resulting intermediate compensation signal to the feedback type second noise filter B for generating a further anti-noise signal, the second compensation signal CS2. For the subtraction, the third mixer M3 may be an additive mixer that comprises a signal inverter on one of its inputs, for instance. The second compensation signal CS2 is superimposed with the audio signal IN, e.g. a music signal, and the first compensation signal CS1 by means of the first mixer M1 for generating the audio output signal, which is converted to the speaker signal SPS by means of the speaker SP.

[0078] The third compensation signal CS3 is generated from the audio signal IN by means of the compensation filter C. The third compensation signal CS3 is provided to third mixer M3, as mentioned above, and in addition to the error compensation unit ECU for a music removal process. In detail, the error compensation unit ECU is configured to adjust the third compensation signal CS3 such that it matches the speaker portion of the disturbed audio signal E. The second mixer M2 of the error compensation unit ECU generates the compensated error signal EM by subtracting the adjusted compensation signal from the disturbed audio signal E such that the compensated error signal EM only, or substantially only, comprises the noise portion of the disturbed audio signal E.

[0079] The adjusted compensation signal is generated from the third compensation signal CS3 by applying filter operations of an adjustable filter element X to the third compensation signal CS3. For example, the adjustable filter element X is an adjustable gain and is adjusted by means of a feedback loop comprising a control unit CTRL that compares the third compensation signal CS3 and the compensated error signal EM and based on this comparison adjusts the gain of the adjustable filter element X. To this end, the control unit CTRL applies an error minimization algorithm, e.g. a least mean squares algorithm, for instance.

[0080] The response of the first noise filter F is adjusted depending on the compensated error signal EM such that a residual noise portion in the disturbed audio signal E is more efficiently removed by means of the first compensation signal CS1, i.e. by means of FF ANC.

[0081] The detection unit DET is configured to estimate an acoustic leakage condition from the response of the first noise filter F or from the disturbed audio signal E and the audio output signal. If a level of the audio signal IN exceeds a predetermined threshold relative to a level of the ambient noise NOISE or noise N, the detection unit DET estimates the acoustic leakage condition from the driver response, i.e. the disturbed audio signal E and the audio output signal, for instance, and otherwise from the response of the first noise filter F. In order to determine whether said threshold is exceeded, the detection unit can be configured to measure a level of the audio portion relative to the noise portion of the disturbed audio signal E, for instance.

[0082] Regarding the estimation of the acoustic leakage condition via the driver response, the detection unit can be configured to compare the audio output signal to the disturbed audio signal and to estimate the acoustic leakage condition based on the result of the comparison, e.g. based on a deviation between the two signals.

[0083] Concerning the estimation of the acoustic leakage condition via the response of the first noise filter F, the detection unit can be configured to monitor the adjustable response of the first noise filter F and to estimate the acoustic leakage condition based on said response. For example, the detection unit is configured to compare the response of the first noise filter F to predetermined responses for estimating the acoustic leakage condition

[0084] The detection engine DET can be configured to generate a leakage value for quantifying the actual leakage condition of the earphone. Consequently, the leakage value is provided to the tuning unit TU for adjusting the response of the compensation filter C such that it matches the driver response, i.e. the transfer function from the speaker SP to the error microphone FB_MIC. For example, the tuning unit TU comprises a memory with a lookup table that comprises a number of reference leakage values and respective associated filter responses. The tuning unit TU is then configured to adjust the response of the compensation filter C by setting one of the associated filter responses depending on the leakage value received from the detection unit DET. The tuning unit TU can further be configured to interpolate the adaptation of the compensation filter C if the leakage value received from the detection unit DET is between two of the reference leakage values.

[0085] In addition, the tuning unit TU can be further configured to adjust the response of the second noise filter B depending on the leakage value received from the detection unit DET, e.g. based on a second lookup table.

[0086] The tuning unit TU, the detection unit DET and the error compensation unit ECU combined essentially constitute the adaptation unit ADP illustrated in FIGS. 1, 2 and 5 and can be arranged as a combined ASIC in a single package, for instance.

[0087] The embodiment of the audio system AS illustrated in FIG. 6 realizes ANC comprising FB ANC and adaptive FF ANC in combination with matching a compensation filter C to the driver response such that both a music compensation and a music removal process can be performed for achieving enhanced ANC taking into account an acoustic leakage without attenuating the wanted input signal IN. Optionally, the FB ANC can likewise be adaptive based on the leakage condition.