CN111862924A

CN111862924A - Audio adjusting method for active noise reduction and related audio adjusting device

Info

Publication number: CN111862924A
Application number: CN201910339768.4A
Authority: CN
Inventors: 卓俊铭; 何维鸿
Original assignee: Realtek Semiconductor Corp
Current assignee: Realtek Semiconductor Corp
Priority date: 2019-04-25
Filing date: 2019-04-25
Publication date: 2020-10-30
Anticipated expiration: 2039-04-25
Also published as: CN111862924B

Abstract

The invention provides an audio frequency adjusting method for active noise reduction and a related audio frequency adjusting device, wherein the audio frequency adjusting method comprises the following steps: the playing frequency is f_kThe single-frequency sound of (a); receiving the single-frequency sound and filtering the single-frequency sound to generate M sets of filter coefficients, wherein each set of filter coefficients in the M sets of filter coefficients comprises a combination of amplitude and phase, and the M sets of filter coefficients are different values from each other; determining an M-th filter coefficient from the M filter coefficients so that the corresponding frequency f_kThe energy of (c) is minimal; and adjusting the single-frequency sound by the mth group of filter coefficients to obtain the corresponding frequency f_kThe adjusted single frequency sound.

Description

Audio adjusting method for active noise reduction and related audio adjusting device

Technical Field

The present invention relates to an audio adjusting method and related apparatus, and more particularly, to a method and related apparatus for improving a noise reduction effect of an Active Noise Cancellation (ANC) earphone.

Background

The noise reduction function is an extremely important part when using earphones to listen to music, wherein passive noise reduction is to slightly reduce the volume of the noise finally transmitted to human ears by the material or the structure of the earphones, but is not much improved for certain types of sound (such as certain unpleasant sounds or sounds of certain frequencies). Compared with passive noise reduction, the active noise reduction effect is more remarkable than the passive noise reduction effect, and therefore more and more earphone products adopt the active noise reduction technology.

However, in the development of active noise reduction earphones, the first problem is that accurate adjustment of the noise reduction degree is required, which needs to consider the response of the earphone structure, the components, the earplugs/ear cups and other materials to the environmental noise, these responses are also often called Primary path responses (Primary path responses), and the processing method in the prior art needs to consider the influence of all the above factors, and the required operations and measurements inevitably need to be implemented by expensive precision instruments (e.g., audio analyzer).

Disclosure of Invention

In view of the high cost of the above precision instruments, the present invention provides a solution with low cost and high noise reduction effect, which can solve the problems faced by the prior art without side effects or with only low side effects.

An embodiment of the present invention provides an audio tuning method for active noise reduction, including: the playing frequency is f_kThe single-frequency sound of (a); receiving the single-frequency sound, and filtering the single-frequency sound to generate M sets of filter coefficients (filtering coefficients), wherein each set of filter coefficients in the M sets of filter coefficients comprises a combination of amplitude and phase, and the M sets of filter coefficients are different values from each other; determining an M-th filter coefficient from the M filter coefficients so that the corresponding frequency f _kThe energy of (c) is minimal; and adjusting the single-frequency sound by the mth group of filter coefficients to obtain the corresponding frequency f_kThe adjusted single frequency sound.

An embodiment of the present invention provides an audio tuning apparatus for active noise reduction, which includes an external sound source, an earphone, an artificial head device, and an audio tuning circuit. The external sound source is used for playing the sound with the frequency f_kThe single-frequency sound of (a); the artificial head device comprises a sound source receiver for receiving the single-frequency sound, wherein the earphone is arranged on the artificial head device; the audio frequency adjusting circuit is coupled with the artificial head device and used for carrying out the following operations: receiving the single-frequency sound and filtering the single-frequency sound to generate M sets of filter coefficientsWherein each of the M sets of filter coefficients comprises a combination of amplitude and phase, and the M sets of filter coefficients are different values from each other; determining an M-th filter coefficient from the M filter coefficients so that the corresponding frequency f_kThe energy of (c) is minimal; and adjusting the single-frequency sound by the mth group of filter coefficients to obtain the corresponding frequency f_kThe adjusted single-frequency sound is provided for the earphone to play.

In summary, the audio adjusting method and the related audio adjusting apparatus of the present invention can improve the noise reduction effect of the active noise reduction earphone in a manner of high fault tolerance and low cost.

Drawings

Fig. 1 is a schematic diagram of an audio tuning device according to an embodiment of the invention.

Fig. 2 is a flow chart of a method of testing an earphone according to an embodiment of the present invention.

Detailed Description

Certain terms are used throughout the description and following claims to refer to particular components. As one of ordinary skill in the art will appreciate, manufacturers may refer to a component by different names. This specification and the claims that follow do not intend to distinguish between components that differ in name but not function. The terms "including" and "comprising" as used throughout this specification and the appended claims are intended to be open-ended and should be interpreted to mean "including, but not limited to. Also, the term "coupled" is used herein to encompass any direct or indirect electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.

The invention provides an active noise reduction circuit comprising a feed-forward filter (filter), which is designed to make the sound played by a speaker as free from surrounding noise as possible, and can obtain the best noise reduction effect by using a simple filter (such as an all-pass filter (APF)) and a plurality of groups of different frequencies through repeated tests (trial and error).

Referring to fig. 1, fig. 1 is a schematic diagram of an audio tuning device 100 according to an embodiment of the present invention, and as shown in fig. 1, the audio tuning device 100 includes a headphone 120 to be tested, an artificial head device 190, an audio tuning circuit 130, and an external sound source 170. The headset 120 may be a wired or wireless headset (e.g., a bluetooth headset) and includes

earmuffs

120L, 120R (where an "earmuff" is understood to be appropriate as an "earbud" if an in-the-canal headset is used); the artificial head device 190 comprises

artificial ears

150L, 150R and an in-ear microphone 160; the audio tuning circuit 130 includes an active noise reduction (ANC) circuit 132, a measurement circuit 134, and an acoustic card 136. The sound card 136 and the in-ear microphone 160 are connected by a sound wire 140, the sound card 136 and the sound source 170 are connected by a sound wire 180, and the in-ear microphone 160 is used for sound reception to simulate the situation of actual human ears hearing sound. It should be noted that the

artificial ears

150L, 150R are structures simulating the structure of human ears, and are suitable for adjustment of ear muff earphones or in-ear earphones. The shape of the artificial head device 190 may approach the true head shape or simply be a column, however, in the case of earmuff style headphones, the headphones should actually span over an object with a sound insulation effect when tested; if in-ear (or in-canal) headphones are tested, the actual head shape or post is not necessarily required, but rather a device that simulates two ear canals is required instead of the artificial head device 190. The external sound source 170 may be implemented using a general speaker, as opposed to the expensive equipment used in the prior art. It should be noted that the effect of the measurement circuit 134 and the sound card 136 can be realized by a software tool (software tool), that is, the present invention is not limited to the measurement circuit and the sound card which need to be provided with hardware, and the same purpose can be achieved by executing a program by a computer.

In the present embodiment, the response of active noise reduction is measured when the user wears the earphone 120 in a state of being assembled, but the present invention is not limited thereto. The artificial head 190 (or

artificial ears

150L, 150R) is used on the basis of the measured environment, and the interior thereof is picked up by the in-ear microphone 160. The above operation is preferably performed in an anechoic chamber (anechoic chamber) which can be further insulated from the outside to ensure the accuracy of the measurement. The present invention is not limited to measuring only one of the

artificial ears

150L, 150R at a time, and the present invention can measure both at the same time. In addition, although the above examples include testing of the left and right ears, the present invention can also be used to test the earphone only on one side, and the method of the present invention can be applied to a single-ear earphone.

The active noise reduction circuit 132 may be a digital circuit including a filter function, and the external measurement circuit 134 may modify the filter coefficient through a control interface, such as a control interface conforming to Universal asynchronous receiver Transmitter/Transmitter (UART), an integrated circuit bus (I2C), or a Bluetooth (BT) specification. The sound card 136 may be built-in or external, and may implement broadcast and recording functions. The circuit 132 may be regarded as a filter including a variable filter coefficient, and the filtering effect may be different due to different filter coefficients.

Referring to fig. 2, fig. 2 is a flowchart of a method 200 for testing the earphone 120 according to an embodiment of the invention. It should be noted that the steps do not necessarily have to be performed in the order of execution shown in fig. 2 if substantially the same results are obtained. The method shown in fig. 2 can be used by the audio tuning apparatus 100 shown in fig. 1, and can be briefly summarized as follows:

step 202: and starting.

Step 204: for frequency f_kAnd playing a single tone sound (single tone).

Step 206: for frequency f_kGenerating M sets of filter coefficients, wherein each set of filter coefficients is H_m[k]Involving a frequency f_kDifferent amplitude (volume) ofCombinations of phases, M being 1 to M (in the case of unknown response, H is generated_m[k]Is high enough so that preferred coefficients are not easily missed), wherein this step can be performed by the active noise reduction circuit 132.

Step 208: respectively calculating and temporarily storing corresponding frequencies f corresponding to the filter coefficients_kTo be compared and to obtain from these filter coefficients the mth set of filter coefficients as the optimum coefficient for the corresponding frequency f_kEnergy P of_m＝E(|c_k*r_m|²) Is at a minimum, where r_mSound signals received for the m-th set of coefficients, c_kTo aim at f _kBand-pass filter (BPF) parameter, E is the sign of the function.

Step 210: checking whether all the coefficients have been calculated (i.e. determining whether the current mth group of coefficients is the last group of coefficients, i.e. mth group of coefficients), if yes, proceeding to step 212; if not, go back to step 208.

Step 212: using the m-th set of filter coefficients as the corresponding frequency f_kWherein the amplitude and phase corresponding to the m-th set of filter coefficients represent f_kThe frequency response of (c).

Step 214: judging whether a next group of tests for other frequencies are needed, if so, returning to the step 204; if not, the process ends.

Frequency f_kMay for example range from 20Hz to 3kHz (the main range for active noise reduction), but the invention is not limited thereto. In step 208, the function symbol E may represent the desired value, i.e. the sound signal r_mThe band-pass filtered signals can be averaged (but the invention is not limited thereto and other methods can be used to average). In addition, the process shown in fig. 2 may be repeatedly executed to calculate the noise reduction coefficients corresponding to the frequencies, so as to obtain the optimal noise reduction response of all the test frequencies, and then determine the filter coefficients of the active noise reduction circuit after obtaining the optimal noise reduction response. The optimal noise reduction response of each frequency feedforward estimated by the method can be used for generating a set of filters with noise reduction effect Wave coefficient. For example, the present invention can use the invfreqz, fitfrd function of MATLAB to generate coefficients, and such coefficients can be applied to various chips of filter circuit with the same function (or directly implemented by Digital Signal Processing (DSP)) to achieve noise reduction effect. In addition, the present invention is not limited to the manner of generating the plurality of sets of coefficients in step 206, and may be implemented by various algorithms, except that the magnitudes and/or phases of the coefficients should be different from each other, otherwise there is no substantial help in solving if repeated values are calculated.

The optimum coefficient described in relation to the process step 208 can be understood as the frequency f to be measured in the process_kThe best performing one of the tried sets of filter coefficients, but because the set of coefficients is only for the frequency f_kPreferably, the other frequencies are not, so that the amplitude and phase corresponding to the m-th set of filter coefficients are recorded as the frequency f_kThe frequency response of (c). Finally, the active noise reduction coefficients to be used by the active noise reduction circuit 132 are a set of coefficients designed for all measured frequency responses to approximate the response of that frequency at each frequency as closely as possible. For example, it can be for frequency f _kThe other N frequencies respectively obtain N specific filter coefficients which can make the energy of the N frequencies minimum, and a final active noise reduction coefficient is determined according to the N specific filter coefficients and the frequency response corresponding to the m group of filter coefficients so as to carry out overall audio frequency adjustment, and the final active noise reduction coefficient can be stored in a chip of the earphone.

In one embodiment, the present invention can be implemented in a laboratory (e.g., anechoic room), so that the audio tuning circuit 130 does not need to be disposed in the headset 120 after the coefficients of the headset 120 are obtained; in another embodiment, the audio tuning circuit 130 can be physically operated in the earphone 120 to match the operation of the user for personal tuning, thereby realizing more diversified applications.

For the earphone manufacturer, how to design the filter coefficients to match the own earphone is the key to influence the noise reduction effect. In the prior art, the material, circuit configuration and the like of each component of the earphone and the influence of the components and the circuit on each other after assembly must be considered when designing the filter coefficient, so that an ideal noise reduction effect cannot be obtained once one parameter is omitted, and an expensive and precise instrument is required for high-precision measurement. By means of the above-described trial and error (trial and error) of the present invention, an ideal noise reduction effect can be achieved with only a simple structure, without requiring expensive, precise instruments. Moreover, the invention is superior to the prior art in that the sound actually heard by human ears is simulated in a forward feedback mode, and then a reverse noise is generated by utilizing a circuit, so that the reverse sound wave can counteract the original noise.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the present invention.

[ notation ] to show

100 audio frequency adjusting device

120 earphone

190 artificial head device

130 audio frequency adjusting circuit

170 external sound source

120L, 120R ear muff (earplug)

150L, 150R artificial ear

160 ear microphone

130 audio frequency adjusting circuit

132 active noise reduction circuit

134 measurement circuit

136 sound card

140. 180 sound source line

170 sound source

200 method

202 to 214.

Claims

1. An audio tuning method for active noise reduction, comprising:

the playing frequency is f_kThe single-frequency sound of (a);

receiving the single-frequency sound and filtering the single-frequency sound to generate M sets of filter coefficients, wherein each set of filter coefficients in the M sets of filter coefficients comprises a combination of amplitude and phase, and the M sets of filter coefficients are different values from each other;

determining an M-th filter coefficient from the M filter coefficients so that the corresponding frequency f_kThe energy of (c) is minimal; and

adjusting the single-frequency sound by the mth group of filter coefficients to obtain the corresponding frequency f_kThe adjusted single frequency sound.

2. The audio tuning method of claim 1, further comprising:

For frequency f_kAcquiring N specific filter coefficients for the N frequencies, respectively, which minimize energy of the N frequencies; and

determining a final active noise reduction coefficient according to the N specific filter coefficients and the frequency response corresponding to the m-th group of filter coefficients, so as to perform overall audio tuning.

3. The audio adjusting method of claim 1, wherein the single-frequency sound is adjusted by the mth set of filter coefficients to obtain the corresponding frequency f_kThe step of adjusting the adjusted single frequency sound comprises:

using the amplitude and phase corresponding to the m-th set of filter coefficients as the frequency f_kThe frequency response of (a); and

according to frequency f_kThe adjusted single frequency sound is determined according to the frequency response.

4. The audio tuning method of claim 1, wherein the corresponding frequency f_kIs of energy P_m＝E(|c_k*r_m|²) Wherein E is a functionSymbol, r_mSound signals received for the m-th set of coefficients, c_kTo aim at f_kThe band-pass filtering parameters of (1).

5. The audio tuning method of claim 1, wherein the operating environment of the audio tuning method is a muffled environment.

6. An audio tuning device for active noise reduction, comprising:

an external sound source for playing the audio signal with frequency f _kThe single-frequency sound of (a);

an earphone;

an artificial head device including a sound source receiver for receiving the single frequency sound, wherein the earphone is disposed on the artificial head device; and

an audio tuning circuit, coupled to the artificial head device, for performing the following operations:

receiving the single-frequency sound, and filtering the single-frequency sound to generate M sets of filter coefficients, wherein each set of filter coefficients in the M sets of filter coefficients comprises a combination of amplitude and phase, and the M sets of filter coefficients are different values from each other;

adjusting the single-frequency sound by the mth group of filter coefficients to obtain the corresponding frequency f_kThe adjusted single-frequency sound is provided for the earphone to play.

7. The audio tuning apparatus of claim 6, wherein the artificial head device comprises an ear structure, and the audio source receiver is disposed in the ear structure.

8. The audio tuning device of claim 6, wherein the operation of the audio tuning circuit further comprises:

for frequency f_kThe other N frequencies respectively obtain the energy of the N frequencies N specific filter coefficients of minimum magnitude; and

9. The audio tuning device of claim 6, wherein the operation of the audio tuning circuit further comprises: using the amplitude and phase corresponding to the m-th set of filter coefficients as the frequency f_kThe frequency response of (a); and

10. The audio tuning device of claim 6, wherein the corresponding frequency f_kIs of energy P_m＝E(|c_k*r_m|²) Wherein E is a function symbol, r_mSound signals received for the m-th set of coefficients, c_kTo aim at f_kThe band-pass filtering parameters of (1).