Audio processing device and associated audio processing method

Abstract

An audio processing device is disclosed. The audio processing device includes a filter and an output circuit. The filter is configured to receive an audio signal to generate a filtered audio signal, wherein the filter includes a plurality of parameters that are adjustable for changing a bandwidth, a center frequency or a gain of response of the filter. The output circuit is configured to receive the filtered audio signal to generate an output audio signal to a speaker. When the parameters of the filter are changed, the filter reduces changes in the audio signal caused by the parameters, and the output circuit continuously receives the filtered audio signal to generate the output audio signal for the speaker to play without interruption.

Claims

1. An audio processing device, comprising: a filter, configured to receive an audio signal to generate a filtered audio signal, wherein transfer function of the filter is H(z)=1+H0*(1−A(z)), H0 is an adjustable gain value, A(z) is a multi-order function controlled by a plurality of parameters, and z is a frequency parameter; and an output circuit, coupled to the filter, configured to receive the filtered audio signal to generate an output audio signal to a speaker; wherein when the transfer function of the filter is changed, the filter reduces the adjustable gain value before the parameters are changed, and the output circuit continuously receives the filtered audio signal to generate the output audio signal for the speaker to play the output audio signal without interruption.

2. The audio processing device of claim 1, wherein before the parameters are changed, the filter gradually reduces the adjustable gain value, to make the transfer function approach a value of one.

3. The audio processing device of claim 2, wherein before the parameters are changed, the filter gradually reduces the adjustable gain value, to make the transfer function be equal to one.

4. The audio processing device of claim 2, wherein during a period after the transfer function approaches one, the filter gradually increases the adjustable gain value to a target value.

5. An audio processing method, comprising: utilizing a filter to receive an audio signal to generate a filtered audio signal, wherein a transfer function of the filter is H(z)=1+H0*(1−A(z)), H0 is an adjustable gain value, A(z) is a multi-order function controlled by a plurality of parameters, and z is a frequency parameter; when the transfer function of the filter is changed, reducing the adjustable gain value before the parameters are changed; and continuously receiving the filtered audio signal to generate an output audio signal, for a speaker to play the output audio signal without interruption during the process of changing the parameters.

6. The audio processing method of claim 5, wherein when the transfer function is changed, the step of reducing the adjustable gain value before the parameters are changed comprises: before the parameters are changed, gradually reducing the adjustable gain value, to make the transfer function approach a value of one.

7. The audio processing method of claim 6, wherein when the transfer function is changed, the step of reducing the adjustable gain value before the parameters are changed comprises: before the parameters are changed, gradually reducing the adjustable gain value, to make the transfer function be equal to one.

8. The audio processing method of claim 6, further comprising: during a period after the transfer function approaches one, gradually increasing the adjustable gain value to a target value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram illustrating an audio processing device according to an embodiment of the present invention.

(2) FIG. 2 is a diagram illustrating that frequency response of a filter is changed.

(3) FIG. 3 illustrates architecture of a filter according to an embodiment of the present invention.

(4) FIG. 4 is a flowchart illustrating an audio processing method according to an embodiment of the present invention.

(5) FIG. 5 is a diagram illustrating that frequency response of a filter is changed according to an embodiment of the present invention.

DETAILED DESCRIPTION

(6) FIG. 1 is a diagram illustrating an audio processing device 100 according to an embodiment of the present invention. As shown in FIG. 1, the audio processing device 100 comprises a filter 110, an output circuit 120 and a control circuit 130, and the audio processing device 100 is configured to process an audio signal Din to generate an output audio signal Dout, which is transmitted to a speaker 104 for playback after being processed by a backend processing circuit 102. In particular, the filter 110 within the audio processing device 100 may be an infinite impulse response (IIR) filter or other types of digital filters, and is configured to perform a filtering operation upon the audio signal Din to generate a filtered audio signal Din′. The output circuit 120 then processes the filtered audio signal Din′ to generate the output audio signal Dout, and the backend processing circuit 102 further performs backend processing upon the output audio signal Dout to generate a signal Vout to the speaker for playback. In one embodiment, the output audio signal Dout may be a digital signal, and the backend processing circuit 102 comprises components such as a digital-to-analog converter and an analog amplifier. In another embodiment, the output circuit 120 comprises a digital-to-analog converter, which means the output audio signal Dout is an analog signal, and the backend processing circuit 102 may comprise an analog amplifier and associated interface circuits. Furthermore, in this embodiment, the audio processing device 100 may be applied to any electronic device that has an audio playback function, such as earphones, loudspeakers, laptop computers, desktop computers, tablets, mobile phones, televisions, etc.

(7) In this embodiment, for the purpose of allowing a user to control the wanted audio quality or audio features, the control circuit 130 within the audio processing device 100 may generate a plurality of control signals Vc according to commands of other components or input signals of the user, to thereby change a bandwidth, a center frequency and/or a gain of response of the filter 110 (e.g. filter response) via changing a plurality of parameters of the filter 110. Taking FIG. 2 as an example for illustration, assuming that an original response of the filter 110 has a bandwidth BW1, a center frequency Fc1 and a gain G1 through parameter setting of the filter 110, the control circuit 130 may change the parameters of the filter 110 according to input signals from the user, to make the response of the filter 110 have a different bandwidth BW2, center frequency Fc2 and gain G2. As there is a need for a stable time period to change the parameters of the filter 110, a mute mechanism may be required to prevent the speaker 104 from playing sound while changing the parameters of the filter 110, in order to prevent the user from hearing abnormal sounds. Adopting this mute mechanism may interrupt audio playback, however, thereby impacting audio quality. This in mind, a transfer function of the filter 110 has a different design, and the control signals Vc generated by the control circuit 130 may be configured to further control the filter 110 in order to prevent abnormal sound during the process of changing the parameters while allowing the speaker 104 to play the audio signal without interruption, to solve the aforementioned problem.

(8) In particular, FIG. 3 illustrates an architecture of the filter 110 according to an embodiment of the present invention, where the architecture shown in FIG. 3 is illustrated using a mathematical form, and the filter 110 comprises a multi-order function A(z), two adders 320 and 340, and a multiplier 330. A transfer function H(z) of the filter 110 may be expressed as H(z)=1+H0*(1−A(z)), where H0 is an adjustable gain value. The multi-order function A(x) may be expressed as b0+b1z.sup.−1+b2z.sup.−2/1+a1z.sup.−+a2z.sup.−2 or other types of multi-order functions, where b0, b1, a1 and a2 are the parameters of the filter 110.

(9) Refer to the flow shown in FIG. 4. In Step 400, the flow starts, and the control circuit 130 receives commands of other components or input signals from the user, which are requests to change the frequency response (i.e. the bandwidth, the center frequency and/or the gain) of the filter 110. In Step 402, the control circuit 130 generates the control signals Vc to gradually reduce (e.g. reduce in a stepwise manner) the adjustable gain value H0 shown in FIG. 3, meaning the filter is controlled to gradually reduce changes in the audio signal Din, making the filtered audio signal Din′ gradually approach the audio signal Din. In detail, when the adjustable gain value H0 is reduced, as the changes H0*A(z) in the audio signal Din caused by the parameters are reduced, the transfer function H(z) of the filter 110 may gradually approach “1”, which makes the filtered audio signal Din′ gradually approach the audio signal Din. In one embodiment, the adjustable gain value may eventually be reduced to zero, so that the filtered audio signal Din′ is substantially equal to the audio signal Din.

(10) In one embodiment, by reducing the adjustable gain value H0 in a stepwise manner, the amount the adjustable gain value H0 is reduced each time may be designed as a gain change amount that is unable to be heard by the user.

(11) In Step 404, in consideration of some timing errors or circuit delay, the control circuit 130 may temporarily stop controlling the filter 110, i.e. wait/delay for a period of time.

(12) In Step 406, the control circuit 130 generates the control signals Vc to directly change the parameters of the filter 110, i.e. change the parameters in the multi-order function A(z). In one embodiment, the parameters of the filter 110 are directly replaced (e.g. with final target values) to accelerate setting and operations of the filter 110, meaning there is no need for indirectly changing or sequentially changing the filter parameters.

(13) In Step 408, in consideration of some timing errors or circuit delay, the control circuit 130 may temporarily stop controlling the filter 110, i.e. wait/delay for a period of time.

(14) In Step 410, the control circuit 130 generates the control signals Vc to gradually increase (e.g. increase in a stepwise manner) the adjustable gain value H0 to a target value, i.e. the filter is controlled to gradually increase changes in the audio signal Din caused by the parameters, to complete the whole flow of changing the parameters of the filter 110. In one embodiment, in the aforementioned process of increasing the adjustable gain value H0 in a stepwise manner, the amount of increasing the adjustable gain value H0 each time may be designed as a gain change amount that is unable to be heard by the user.

(15) It should be noted that Steps 404 and 408 are optional steps; i.e. Steps 404 and 408 may be removed from the flow without affecting main operations of the present invention.

(16) FIG. 5 is a diagram illustrating the flow of changing the parameters of the filter 110 shown in FIG. 4. In FIG. 5, the frequency response of the filter 110 originally has the bandwidth BW1, the center frequency Fc1 and the gain G1. Before the parameters of the filter 110 need to be changed, the adjustable gain value H0 may be gradually reduced to make the frequency response thereof approach “1”. After setting of the filter parameters is completed, the adjustable gain value H0 may be gradually increased, to make the frequency response of the filter 110 have the bandwidth BW2, the center frequency Fc2 and the gain G2.

(17) In the above process of changing the parameters of the filter 110, the output circuit 120 may keep generating the output audio signal Dout to the backend processing circuit 102 in order to generate the signal Vout to the speaker 104 for playback without interruption. As the filtered audio signal Din′ is substantially equal to the audio signal Din when the parameters are being changed and the filter is in an unstable state, during the whole process of changing the parameters, normal audio quality can be provided for the user without any mute mechanism, so the problem mentioned in the related art can be effectively solved.

(18) Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.