NOISE CANCELLATION SYSTEM, NOISE CANCELLATION HEADPHONE AND NOISE CANCELLATION METHOD

Abstract

A noise cancellation system for a noise cancellation enabled audio device comprises a first noise filter and a second noise filter, each being designed to process a noise signal, a combiner and an adaptation engine. The first noise filter has a first fixed frequency response matched to a high leakage condition of the audio device. The second noise filter has a second fixed frequency response matched to a low leakage condition of the audio device. The combiner is configured to provide a compensation signal based on a combination of an output of the first noise filter amplified with a first adjustable gain factor and an output of the second noise filter amplified with a second adjustable gain factor. The adaptation engine is configured to estimate a leakage condition of the audio device based on an error noise signal and to adjust at least one of the first and the second adjustable gain factors based on the estimated leakage condition.

Claims

1. A noise cancellation system for a noise cancellation enabled audio device, in particular headphone, the system comprising a first noise filter having a first fixed frequency response matched to a high leakage condition of the audio device and being designed to process a noise signal; a second noise filter having a second fixed frequency response matched to a low leakage condition of the audio device and being designed to process the noise signal; a combiner configured to provide a compensation signal based on a combination of an output of the first noise filter amplified with a first adjustable gain factor and an output of the second noise filter amplified with a second adjustable gain factor; and an adaptation engine configured to estimate a leakage condition of the audio device based on an error noise signal and to adjust at least one of the first and the second adjustable gain factors based on the estimated leakage condition.

2. The noise cancellation system according to claim 1, wherein the adaptation engine is configured to adjust the at least one of the first and the second adjustable gain factors during operation of the noise cancellation system.

3. The noise cancellation system according to claim 1, wherein the adaptation engine is configured to estimate the leakage condition based on a noise evaluation of the error noise signal at one or more distinct frequencies or frequency ranges.

4. The noise cancellation system according to claim 1, wherein the adaptation engine is configured to estimate the leakage condition based on a filtered version of the error noise signal.

5. The noise cancellation system according to claim 1, wherein the adaptation engine is configured to adjust the first and the second adjustable gain factor using a mapping function, in particular polynomial mapping function, between the estimated leakage condition and the first and the second adjustable gain factor.

6. The noise cancellation system according to claim 1, wherein the adaptation engine is configured to adjust the first and the second adjustable gain factor further based on an external input, in particular a user input.

7. The noise cancellation system according to claim 1, wherein the combiner is further configured to provide the compensation signal based on the combination amplified with a supplementary adjustable gain factor and wherein the adaptation engine is further configured to adjust the supplementary adjustable gain factor based on the estimated leakage condition.

8. The noise cancellation system according to claim 1, wherein the error noise signal is a feedback noise signal recorded by a feedback noise microphone located in proximity to a speaker of the audio device.

9. The noise cancellation system according to claim 1, wherein the first noise filter and the second noise filter are each of a feedforward noise cancellation type; the noise signal is an ambient noise signal, in particular recorded by an ambient noise microphone of the audio device; and the error noise signal is a feedback noise signal, in particular recorded by a feedback noise microphone located in proximity to a speaker of the audio device.

10. The noise cancellation system according to claim 9, wherein the adaptation engine is configured to estimate the leakage condition based on a ratio between the error noise signal and the noise signal at one or more distinct frequencies or frequency ranges.

11. The noise cancellation system according to claim 1, wherein the first noise filter and the second noise filter are each of a feedback noise cancellation type; and the noise signal is the error noise signal, which is a feedback noise signal, in particular recorded by a feedback noise microphone located in proximity to a speaker of the audio device.

12. The noise cancellation system according to claim 9, the system further comprising a third noise filter being of a feedback noise cancellation type, having a third fixed frequency response matched to the high leakage condition of the audio device and being designed to process the error noise signal; a fourth noise filter being of a feedback noise cancellation type, having a fourth fixed frequency response matched to the low leakage condition of the audio device and being designed to process the error noise signal; wherein the compensation signal is a feedforward compensation signal; the combiner is configured to provide a feedback compensation signal based on a combination of an output of the third noise filter amplified with a third adjustable gain factor and an output of the fourth noise filter amplified with a fourth adjustable gain factor; and the adaptation engine is further configured to adjust the third and fourth adjustable gain factors based on the estimated leakage condition.

13. The noise cancellation system according to claim 1, the system further comprising one or more further noise filters, each having a further fixed frequency response matched to a distinct medium leakage condition of the audio device and being designed to process the noise signal; wherein the combiner is configured to provide the compensation signal based on a combination of the output of the first noise filter amplified with the first adjustable gain factor, the output of the second noise filter amplified with the second adjustable gain factor and respective outputs of the one or more further noise filters, each amplified with a respective further adjustable gain factor; and the adaptation engine is further configured to adjust the respective further adjustable gain factors based on the estimated leakage condition.

14. A noise cancellation enabled audio device, in particular headphone or handset, comprising a noise cancellation system according to claim 1, a speaker and a feedback noise microphone located in proximity to the speaker for providing the error noise signal.

15. An audio player comprising a noise cancellation system according to claim 1.

16. A noise cancellation method for a noise cancellation enabled audio device, in particular headphone, the method comprising processing a noise signal with a first noise filter having a first fixed frequency response matched to a high leakage condition of the audio device; processing the noise signal with a second noise filter having a second fixed frequency response matched to a low leakage condition of the audio device; generating a compensation signal based on a combination of an output of the first noise filter amplified with a first adjustable gain factor and an output of the second noise filter amplified with a second adjustable gain factor; estimating a leakage condition of the audio device based on an error noise signal; and adjusting at least one of the first and the second adjustable gain factors based on the estimated leakage condition.

17. The method according to claim 16, wherein the error noise signal is a feedback noise signal recorded by a feedback noise microphone located in proximity to a speaker of the audio device.

18. The method according to claim 17, wherein the first noise filter and the second noise filter are each of a feedforward noise cancellation type; and the noise signal is an ambient noise signal recorded by an ambient noise microphone of the audio device.

19. The method according to claim 17, wherein the first noise filter and the second noise filter are each of a feedback noise cancellation type; and the noise signal is the error noise signal.

20. The method according to claim 16, wherein the at least one of the first and the second adjustable gain factors is adjusted during operation of the noise cancellation audio device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The improved signal processing 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.

[0038] In the drawings:

[0039] FIG. 1 shows a schematic view of a headphone; and

[0040] FIGS. 2 to 6 show different implementation examples of a noise cancellation system.

DETAILED DESCRIPTION

[0041] FIG. 1 shows a schematic view of an ANC enabled 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 FB_MIC and an ambient noise microphone FF_MIC. The feedback noise microphone FB_MIC is particularly directed or arranged such that it records both ambient noise and sound played over the speaker SP. Preferably the feedback noise 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 microphone FF_MIC is particularly directed or arranged such that it mainly records ambient noise from outside the headphone HP.

[0042] 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 feedback noise microphone FB_MIC may be used according to the improved signal processing concept to provide an error noise 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.

[0043] ANC performance usually depends on this wearing condition because the filter characteristics of an ANC filter are conventionally trimmed to a specific condition. For example, this condition determines how tight or sealed the headphone HP, taken as an example for audio devices, is positioned against the user. If the headphone HP is moved, this condition changes and so do the acoustic properties. For instance, the headphone can be worn in a low leakage condition, where only a small amount of ambient noise can enter the headphone and reach the feedback microphone FB_MIC. In another wearing condition, a high leakage condition, ambient noise can reach inside the headphone and the feedback microphone FB_MIC. Various conditions exist in between these two extremes.

[0044] Referring now to FIG. 2, a schematic block diagram of an example implementation of the improved signal processing concept is shown. The implementation comprises a first noise filter HLF and a second noise filter LLF, which are both input with a noise signal n0, such that both filters process the same signal. A first noise filter HLF has a first fixed frequency response that is matched to the high leakage condition of the audio device, for example the headphone HP. The second noise filter has a second fixed frequency response that is matched to the low leakage condition of the audio device. Accordingly, the output of the first noise filter HLF alone could be used for ANC processing if the audio device is in the high leakage condition. Similarly, if the audio device is in the low leakage condition, the output of the second noise filter LLF could be used for ANC processing alone.

[0045] The implementation further includes a combiner CMB that combines the outputs of the first and the second noise filter HLF, LLF amplified with a first adjustable gain factor G1 and a second adjustable gain factor G2, respectively. For example, the combination is performed by summing up the amplified versions of the filter output signals. This sum can be directly used as a compensation signal cm or optionally be amplified with a supplementary gain factor GS. The compensation signal cm may then be used by an audio processor AUD that combines the compensation signal cm with a useful audio signal s0 according to the implemented ANC structure. The output of the audio processor AUD, which may also include amplifiers etc., is then output to the speaker SP of the audio device.

[0046] The gain factors G1 and G2 and, optionally, GS, are adjusted by an adaptation engine ADP that is configured to estimate a leakage condition of the audio device based on an error noise signal nerr provided by the feedback microphone FB_MIC. The adaptation engine ADP adjusts the first and the second adjustable gain factor G1, G2 and, optionally, GS, based on the estimated leakage condition. For example, the adjustment of the at least one of the adjustable gain factors G1, G2 and, optionally, GS, is made during operation of the noise cancellation arrangement or the audio device including the arrangement.

[0047] As mentioned above, there is a relationship between an actual leakage condition and the amount of noise, in particular ambient noise that is able to enter the audio device and reach the feedback microphone FB_MIC. Hence, the adaptation engine e.g. performs a noise evaluation of the error noise signal nerr, for example at one or more frequencies or frequency ranges. For example, the selected frequencies are significant for ambient noise. As described above, the evaluation can be performed in the time domain as well as in the frequency domain with respective signal processing approaches.

[0048] The adaptation engine ADP may use a mapping function, e.g. a polynomial mapping function between the estimated leakage condition and the adjustable gain factors G1, G2 and GS. For example, the higher the leakage condition, the higher the gain factor G1 for the first noise filter while the second gain factor G2 for the second noise filter will decrease accordingly. Similarly, the lower the leakage condition is estimated to be, the greater the second gain factor G2 will be while decreasing the first gain factor G1.

[0049] The adaptation engine ADP may optionally be configured to adjust the first and the second adjustable gain factors G1, G2 further based on an external input extu, which may be a user input. For example, the external input extu determines or manipulates the mapping function between leakage condition and gain factors G1, G2 and GS. However, the external input extu may also affect the evaluation of the error noise signal nerr. For example, the external input extu may select the way of estimating the leakage condition, thereby having influence on e.g. the speed of estimation and setting of the gain factors G1, G2 and GS.

[0050] Accordingly, by controlling the mix of the two filters HLF, LLF, a resultant filter is produced which is a mix of the two filters HLF, LLF. As the actual leakage condition will continually change due to movement of a user's head, for the headphone example, so too does the resultant filter response. At any one time, the resulting filter response is a linear interpolation of the two noise filters.

[0051] The general concept for improved signal processing which has been described in conjunction with FIG. 2, will now be explained in more detail for feedforward noise cancellation systems in FIG. 3, a feedback noise cancellation system in FIG. 4 and a hybrid noise cancellation system in FIG. 6. FIG. 5 shows a general extension of the concept shown in FIG. 2. In conjunction with these figures, only the differences to the implementation of FIG. 2 may be explained. Features from FIG. 2 left out in the following Figures may nevertheless be used in these Figures.

[0052] Referring now to FIG. 3, which shows a feedforward noise cancellation system, the noise signal n0 is provided by a feedforward microphone FF_MIC, as for example shown in FIG. 1 and serving the general purpose of providing a sole ambient noise signal. The audio processor AUD is therefore adapted accordingly in order to perform feedforward ANC.

[0053] The ambient noise signal n0 may optionally be provided to the adaptation engine ADP, which in such a configuration may be configured to estimate the leakage condition based on a ratio between the error noise signal nerr and the noise signal n0 at one or more distinct frequencies or frequency ranges. This allows to determine how much of the ambient noise recorded with the feedforward microphone FF_MIC, which can also be called an ambient noise microphone, is also present in the error noise signal nerr. Accordingly, the leakage condition can be estimated based on a relative value instead of an absolute value at the distinct frequencies, resulting in an improved estimation performance.

[0054] Referring now to FIG. 4, a feedback ANC system is shown, where the error noise signal nerr is also used as an input for the first and the second noise filters HLF, LFF. The audio processor AUD in this implementation is adapted accordingly to perform the feedback ANC based on the combined filter output. To this end, also the feedback error signal nerr provided to the feedback filters may be pre-processed by the audio processor AUD based on the useful audio signal s0, in order to take into account the portions of the useful audio signal s0 in the feedback error signal nerr.

[0055] Even if only feedback ANC is performed, but an ambient noise microphone like the microphone FF_MIC is present, the estimation on the leakage condition could also be performed using noise ratios between the error noise signal nerr and the noise signal provided by the ambient noise microphone, as described above for FIG. 3.

[0056] Referring now to FIG. 5, the basic concept shown in FIG. 2 is extended by using a further noise filter MLF having a further fixed frequency response that is matched to a medium leakage condition of the audio device. The medium leakage condition is particularly somewhere in between the high leakage condition and the low leakage condition. Accordingly, the compensation signal cm is formed in the combiner CMB by additionally summing up the output of the further noise filter MLF amplified with an adjustable gain factor GM.

[0057] The adaptation engine ADP in this implementation is hence further configured to adjust not only the first and the second gain factor G1, G2, but also the gain factor GM based on the estimated leakage condition. For example, one of the gain factors G1 and G2 can be set to zero if the estimated leakage condition is between the leakage condition associated with the further noise filter MLF and the respective other extreme leakage condition, such that it is only interpolated between two of the noise filters being matched closest to the actual leakage condition.

[0058] Further noise filters are matched to respective distinct leakage conditions. Moreover, the extension to three or more noise filters can both be applied to feedforward ANC and feedback ANC.

[0059] Referring now to FIG. 6, the general concept described in conjunction with FIG. 2 is applied to a hybrid ANC implementation employing both feedforward and feedback ANC. Accordingly in this implementation, two filter pairs are present, one for the feedforward part and one for the feedback part. In particular, the feedforward part includes a first feedforward noise filter HLF FF matched to the high leakage condition and a second feedforward filter LLF FF matched to the low leakage condition. Similarly, for the feedback part, there is one filter HLF_FB matched to the high leakage condition and a filter LLF_FB matched to the low leakage condition. Each of the four filters is associated with a respective adjustable gain factor G1, G2 for the feedforward part and G3, G4 for the feedback part, each adjusted by the adaptation engine ADP according to the concept described above. The audio processor AUD uses the compensation signal cmff produced by the feedforward part and the feedback compensation signal cmfb for implementing the hybrid ANC. As explained above for FIG. 4, also the feedback error signal nerr provided to the feedback filters may be pre-processed by the audio processor AUD based on the useful audio signal s0, in order to take into account the portions of the useful audio signal s0 in the feedback error signal nerr.

[0060] A supplementary gain factor GS, shown in the previous implementations, has been left out of the example implementation of FIG. 6. However, one or both of the feedforward part and the feedback part can use a respective supplementary gain factor as well.

[0061] It should be noted that in all of the implementations described above, neither of the microphones FF_MIC, FB_MIC nor the speaker SP are essential parts of a noise cancellation system according to the improved signal processing concept. Even the audio processor AUD could be provided externally. For example, such a noise cancellation system could be implemented both in hardware and software, for example in a signal processor. The noise cancellation system can be located in any kind of audio player, like a mobile phone, an MP3 player, a tablet computer or the like. However, the noise cancellation system could also be located within the audio device, e.g. a mobile handset or a headphone, earphone or the like.