Low-complexity feedback suppression for portable karaoke

Abstract

A low-complexity feedback suppression system and method for a portable karaoke system is provided. The feedback suppression system includes at least one microphone for capturing an input signal including a source signal and acoustic feedback propagated through the environment, an electrical acoustic path for compressing and equalizing the input signal and providing it to an output signal after amplification, and a loudspeaker for reproducing the output signal. In the feedback suppression, at least one infinite impulse response (IIR) filter is introduced to estimate the acoustic feedback picked up by the microphone from the real environment, thereby canceling the acoustic feedback from the microphone input signal.

Description

[Technical field]

[0001] The present invention relates generally to acoustic feedback cancellation techniques, and more particularly to a low-complexity feedback suppression method and system for portable karaoke systems. [Background technology]

[0002] Karaoke has become more and more popular as an interactive entertainment activity in East Asia. Anyone can sing with friends at a karaoke club using a karaoke machine. Recently, people are not satisfied with just singing at clubs, but are singing everywhere with portable all-in-one karaoke machines and other devices. For this reason, many portable karaoke products have entered the market. However, the sound quality of most of these products is not as good as expected. Many of these products have "acoustic feedback" or do not have enough volume due to this feedback problem.

[0003] In fact, feedback is a common problem in karaoke or public address systems. Karaoke systems usually consist of at least one microphone and a loudspeaker. When an audio signal is picked up by the microphone and subsequently amplified and fed to the loudspeaker, the sound of the loudspeaker is usually picked up by the microphone via a direct acoustic path or some reflected paths. The acoustic coupling between the loudspeaker and the microphone results in a closed signal loop, which may result in acoustic feedback in the form of unwanted feedback. In this case, it may cause feedback problems, damage the loudspeaker, or limit the performance of the public address system by limiting the amount of amplification that can be applied if the karaoke system needs to be stable.

[0004] Therefore, various measures are taken to prevent this problem. There are four main categories of feedback suppression methods. The first is the frequency shift method, which can vary the microphone input signal with a frequency shift of a few Hz per loop. Larger shift frequencies, for example 20 Hz, are more effective, but the side effects on the sound quality are too severe to be acceptable. Therefore, not much modification can usually be made and the suppression performance must be compromised. The second is notch filter-based feedback suppression (NFS), which uses a notch filter to suppress the problematic frequencies where feedback is detected. A notch filter is a stopband filter with a very narrow stopband, which can significantly reduce the gain of certain frequency bands and thus suppress those frequencies from the microphone input signal. However, NFS methods usually include a detection and suppression phase, in the sense that the feedback sound must be detected first, and therefore the feedback sound can often be heard before it is suppressed. The third is the beamforming method, which uses a microphone array or a loudspeaker array to modify the directivity and reduce the direct sound propagation between the microphone and the loudspeaker. However, this method requires additional hardware and more computation, which often limits the number of microphones and loudspeakers. The fourth method is Acoustic Echo Cancellation (AEC), which uses an adaptive filter to approximate the transfer function between the microphone and the loudspeaker, and filters the output signal from the loudspeaker to cancel the approximated feedback signal picked up by the microphone. If the transfer function is perfectly approximated by the adaptive filter, no feedback will occur. Although AEC methods usually perform well thanks to their adaptation mechanism, they require high computation and power consumption, as well as long system processing time, making them unsuitable for portable karaoke systems that require constant playback and delay times.

[0005] However, most of these measures focus on typical large karaoke systems, where the distance between the loudspeaker and the microphone is usually much farther than in portable all-in-one karaoke systems. On the other hand, users will still want to sing as loud as possible even with such small karaoke machines. Therefore, if karaoke products want to exceed users' expectations, they need to develop better technologies to suppress feedback. Summary of the Invention [Means for solving the problem]

[0006] The present invention overcomes some of the above-mentioned drawbacks by providing a low-complexity feedback suppression system for a portable karaoke system. The feedback suppression system comprises at least one microphone for capturing an input signal including a source signal and acoustic feedback propagated through the environment, an electrical acoustic path for compressing and equalizing the input signal and providing it to an output signal after amplification, and a loudspeaker for reproducing the output signal. The feedback suppression system further comprises at least one infinite impulse response (IIR) filter for estimating the acoustic feedback, thereby canceling the acoustic feedback from the input signal.

[0007] The present invention further provides a low-complexity feedback suppression method for a portable karaoke system, comprising the steps of capturing an input signal including a source signal and acoustic feedback via at least one microphone, compressing and equalizing the input signal in an electrical acoustic path, and then amplifying and then feeding an output signal to a loudspeaker, where the output signal is reproduced on the loudspeaker and propagates through an environment. The feedback suppression method further comprises estimating the acoustic feedback via at least one infinite impulse response (IIR) filter, thereby cancelling the acoustic feedback from the input signal. The present specification also provides, for example, the following: (Item 1) 1. A low-complexity feedback suppression method for a portable karaoke system, comprising: capturing, by at least one microphone, an input signal including a source signal and acoustic feedback; in an electrical acoustic path, compressing and equalizing said input signal and then amplifying it before providing it to an output signal; reproducing, by a loudspeaker, said output signal for propagation through an environment; Including, The method further comprises estimating the acoustic feedback by at least one infinite impulse response (IIR) filter, thereby canceling the acoustic feedback from the input signal. The low-complexity howling suppression method. (Item 2) 2. The method of claim 1, wherein the acoustic feedback comprises feedback generated in a closed signal loop caused by acoustic coupling between the loudspeaker and the at least one microphone. (Item 3) 2. The method of claim 1, further comprising the step of modeling an environmental transfer function by the at least one IIR filter. (Item 4) 4. The method of claim 3, wherein a relative position of the at least one microphone and the loudspeaker is fixed. (Item 5) 4. The method of claim 3, wherein modeling the environmental transfer function includes measuring and estimating it offline and approximating it. (Item 6) 6. The method of claim 5, wherein approximating the environmental transfer function can be performed by a multi-band IIR filter. (Item 7) 4. The method of claim 3, further comprising decorrelating the output signal from the input signal. (Item 8) 8. The method of claim 7, wherein decorrelating the output signal from the input signal can be performed by frequency shifting the input signal. (Item 9) 2. The method of claim 1, further comprising arranging the at least one microphone with different directionality as a microphone array for beamforming. (Item 10) 10. The method of claim 9, wherein the microphone array forms a cardioid directional pattern. (Item 11) 1. A portable karaoke system with low complexity feedback suppression, comprising: at least one microphone for capturing an input signal including a source signal and acoustic feedback propagating through the environment; an electroacoustic path for compressing and equalizing said input signal and then amplifying it before providing an output signal; a loudspeaker for reproducing said output signal; Equipped with the system further comprising at least one infinite impulse response (IIR) filter for estimating the acoustic feedback and thereby cancelling the acoustic feedback from the input signal. The portable karaoke system. (Item 12) 12. The system of claim 11, wherein the acoustic feedback comprises feedback generated in a closed signal loop caused by acoustic coupling between the loudspeaker and the at least one microphone. (Item 13) Item 12. The system of item 11, wherein the at least one IIR filter further models an environmental transfer function. (Item 14) Item 14. The system of item 13, wherein the relative positions of the at least one microphone and the loudspeaker are fixed. (Item 15) 14. The system of claim 13, wherein the at least one IIR filter further measures and estimates the environmental transfer function offline and approximates it. (Item 16) Item 16. The system of item 15, wherein the environmental transfer function can be approximated by a multi-band IIR filter. (Item 17) Item 14. The system of item 13, further comprising decorrelating the output signal from the input signal. (Item 18) Item 18. The system of item 17, wherein decorrelating the output signal from the input signal can be performed by frequency shifting the input signal. (Item 19) Item 12. The system of item 11, wherein the at least one microphone is further arranged with different directivities as a microphone array for beamforming. (Item 20) 20. The system of claim 19, wherein the microphone array forms a cardioid directional pattern.

[0008] The invention may be better understood from reading the following description of non-limiting embodiments, with reference to the accompanying drawings, in which like reference numbers indicate corresponding parts, and in which: [Brief description of the drawings]

[0009] [Figure 1] 1 shows an example of a feedback scenario in a karaoke system with one microphone and one loudspeaker. [Figure 2A] 1 shows an exemplary system diagram for feedback suppression in a karaoke system in accordance with the present invention; [Figure 2B] 1 shows an exemplary system diagram for feedback suppression in a karaoke system in accordance with the present invention; [Diagram 3] 2 shows an exemplary flow chart illustrating a feedback suppression method according to the present invention. [Figure 4] 1 illustrates an exemplary hardware system for a portable all-in-one karaoke system according to the present invention. [Figure 5A] FIG. 1 illustrates some simulated comparative results relevant to the present invention, showing spectrograms of loudspeaker signals. [Figure 5B]FIG. 1 illustrates some simulated comparative results relevant to the present invention, showing spectrograms of a loudspeaker signal containing feedback sounds around 2 kHz and 9.3 kHz. [Figure 5C] FIG. 1 shows some simulated comparative results related to the present invention, showing spectrograms obtained with the frequency shifting method. [Figure 5D] FIG. 1 shows some simulated comparative results related to the present invention, showing spectrograms obtained with the NFS method. [Figure 5E] FIG. 1 shows some simulated comparative results related to the present invention, FIG. 2 shows a spectrogram obtained with the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Although a detailed description of one or more embodiments of the present invention is disclosed below, it should be understood that the disclosed embodiments are merely exemplary of the present invention, which may be embodied in various and alternative forms. The figures are not necessarily to scale, and some features may be exaggerated or minimized to show details of specific components. Therefore, specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for teaching those skilled in the art to variously use the present invention.

[0011] Fig. 1 shows an example of a feedback scenario in a karaoke system with one microphone and one loudspeaker. As seen in Fig. 1, the system 100 includes a microphone 110 and a loudspeaker 140, where the microphone 110 is connected to an electroacoustic path 120, which is then amplified at 130 and then connected to the loudspeaker. When the karaoke system is set up, a source signal S(z) from a user's singing voice is captured by the microphone 110, and an input signal X(z) is processed in the electroacoustic path G(z), including compression and equalization, and amplified with a gain factor K. An output signal Y(z) is fed to the loudspeaker 140 and propagated through the environment 150.

[0012] When an acoustic signal is picked up by the microphone 110 and subsequently amplified and fed to the loudspeaker 140, the sound reproduction by the loudspeaker 140 can be picked up by the microphone 110 through a direct path or a reflected path. The acoustic coupling between the loudspeaker 140 and the microphone 110 results in an output signal Y(z) propagated through the environmental transfer function F(z) to form acoustic feedback, which is then also picked up by the microphone 110, and thus the signal X(z) shown in FIG. 1 includes both the source signal S(z) and the acoustic feedback Y(z)·F(z).

[0013] Therefore, with all signals and transfer functions expressed in the frequency domain, the process in Figure 1 can be expressed as Y(z)=X(z)·G(z)·K (1) X(z)=Y(z)·F(z)+S(z) (2)

[0014] With regard to equation (2) above, it is contemplated that the input signal X(z) to the karaoke system may further include an audio stream, omitted here, such as music accompaniment to the song input via Bluetooth® or an AUX interface.

[0015] And then we can calculate the total transfer function H(z) from the source signal S(z) to the output signal Y(z):

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[0016] Many methods for feedback suppression have been discussed in the past decades. Indeed, the first precaution to be taken is to optimize the entire karaoke system, including the directivity of the loudspeakers and microphones, the distance between them, the overall gain of the system, and the amplitude of potentially problematic frequencies. However, optimization is usually limited, especially for portable all-in-one karaoke systems, because of certain requirements for their form factor and sound performance, which are as small in size and as high in sound level as possible. In these limited scenarios, it is necessary to automate the process or take other measures to avoid feedback feedback. Therefore, the present invention provides a portable all-in-one karaoke system with a low-complexity feedback suppression method.

[0017] In order to better suppress the feedback sound of the portable all-in-one karaoke machine and reduce the processing calculation, power consumption and system delay time, the present invention provides a low-complexity feedback suppression method for a portable karaoke system, in which a filter is used to cancel the unwanted components from the microphone signal.

[0018] FIG. 2A shows an exemplary system diagram for feedback suppression in a karaoke system according to the present invention. A filter 260 is introduced in this system 200, F estF(z) is the estimated transfer function established by a filter 260 designed and adapted to resemble the actual environmental transfer function F(z) in the environment 250. Many algorithms have been proposed to realize this method, such as the least mean square algorithm and the normalized least mean square algorithm. In the example of FIG. 2A, F est (z) completely converges, so F est (z) = F(z), X est If (z)=X(z), all feedback signals from the loudspeaker 240 are cancelled, so that the input signal consists only of the source signal S(z), such as from the user's singing voice, but no feedback occurs. This can be expressed as the following equation: X(z)-X est (z) = S(z) + F(z) Y(z) - F est (z)Y(z)≒S(z) (5)

[0019] Using an adaptive filter to estimate the environmental transfer function can achieve a good effect of suppressing howling. However, in practice, there are still some problems in howling suppression by an adaptive filter estimating the environmental transfer function. First, the delay time may not meet the requirements of this small karaoke machine. While the loudspeaker is very close to the microphone, the adaptive algorithm may require a long processing time, so the sound propagation time will probably be shorter than the processing time, and therefore the algorithm will be ineffective. Second, the adaptive algorithm may also consume a large amount of power, which will cause the battery to be quickly depleted, which is an obvious disadvantage for portable devices. Third, the adaptive algorithm may not converge smoothly, which will result in a large difference in the adaptive filter, which will always affect the timbre of the user's singing. In addition, there is a high correlation between the loudspeaker and microphone of the karaoke system, which will reduce the performance of this structure in this scenario.

[0020] Therefore, in the example system, several second-order infinite impulse response (IIR) filters 260′ are used to model the transfer function F(z), as shown in FIG. 2B. Since the form factor of the portable all-in-one karaoke system dictates a fixed distance between the loudspeaker 240 and the microphone 210, the transfer function F iir (z) can be measured and estimated offline and approximated by a multi-band IIR filter. In addition, in certain situations such as integrated karaoke machines, the relative positions of the loudspeaker and microphone are relatively fixed, so even if no adaptation process is required, 80-90% of the feedback suppression effect can be achieved, and the IIR filter can have a fixed suppression effect. Using an IIR filter in this system not only saves power consumption, but also saves the computing resources of the chip.

[0021] Additionally, decorrelation 215 can be further introduced into the example system 200 to reduce correlation between the loudspeaker signals and the microphone signals. In the model shown in FIG. 2B, the loudspeaker signals are decorrelated from the microphone signals by frequency shifting the input signals before compression and equalization. This means that in decorrelation 215, the total input signal X(z)-X iir (z) is frequency shifted to Y(z) and X(z)-X iir The result in (z) is decorrelated. Thus, the output signal is decorrelated from the input signal. For example, a frequency-shifted output signal x shift (t) can be obtained in the time domain as follows:

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[0022] The full advantage of frequency shifting can be taken in the present method. In the proposed model using several IIR filters to model the environmental transfer function, no adaptive processing is required due to the time delay problem and high power consumption. Furthermore, since the loudspeaker output signal returns to the input microphone through some acoustic coupling in the air, which creates the acoustic feedback problem, the frequency shift is used to decorrelate the reference and error signals, which can be used to mitigate the biased filter estimation.

[0023] FIG. 3 shows an exemplary flow chart illustrating a feedback suppression method according to the present invention.

[0024] In step 310, an input signal including a source signal, such as a user's singing voice, and acoustic feedback is provided to the portable karaoke system. This portion of the input signal is captured by at least one microphone. Furthermore, the input signal may further include an audio stream, such as music accompanying the song, and this portion of the input signal may be uploaded to the karaoke system in a wired or wireless manner, such as via Bluetooth or an AUX interface.

[0025] In step 315, decorrelation is introduced into the provided system to decorrelate the input signal. In this step, the loudspeaker signals of the loudspeakers are decorrelated from the input signal by frequency shifting the input signal.

[0026] In step 320, the frequency shifted input signal is processed in an electroacoustic path, including compression and equalization, and then amplified by a gain factor K to obtain an output signal.

[0027] In step 340, the output signal is fed to loudspeakers for reproduction and propagation through the environment.

[0028] In this step, the output signal reproduced from the loudspeaker, after propagating in the environment, is picked up by the microphones either directly or via several reflected paths as acoustic feedback, which enters the microphones as another part of the input signal received by at least one microphone, as described above in step 310.

[0029] Next, in step 360, the environmental transfer function is modeled using several IIR filters to cancel undesired components from the microphone signal. This step involves measuring and estimating the environmental transfer function offline, approximating the function, such as by a multi-band IIR filter. The resulting estimated signal is approximately equal to the acoustic feedback portion of the input signal entering the microphone in step 350. Thus, by subtracting the estimated acoustic feedback from the input signal captured by the microphone, the acoustic feedback that may generate howling in the system can be cancelled.

[0030] 4 shows an exemplary hardware system for a portable all-in-one karaoke system according to the present invention, in which the low-complexity feedback suppression method provided herein is implemented. As shown in FIG. 4, the feedback suppression method additionally uses beamforming techniques to change the directivity using a microphone array or loudspeaker array.

[0031] As an example, two microphones with different directivities are used as the microphone array 410 to form a cardioid directional pattern as shown in Fig. 4. This can also be considered as a special beamforming arrangement to suppress more feedback components. It can be understood that more microphones can be used to arrange the microphone array.

[0032] Beamforming Output X beam (z) is written as: X beam(z)=Σ k W k (z)·X k (z) (7) Here, W k (z) and X k (z) is the kth beamforming filter and the kth microphone input signal, respectively.

[0033] Additionally, in a real portable karaoke product, the microphone 410 may be wrapped in sound absorbing cotton 480 to further reduce the acoustic energy from the loudspeaker 440. As shown diagrammatically in Figure 4, it can be seen that a passive radiator 470 is used instead in this example machine.

[0034] Figures 5A-5E show some simulated comparison results. Figure 5A shows the spectrogram of the loudspeaker signal, and Figure 5B shows the howling sounds around 2kHz and 9.3kHz. The howling sounds increase dramatically and continue to the end. In the frequency shift method of Figure 5C, the howling frequencies are shifted down for each loop and their power is suppressed at a lower level, but the howling is still noticeable. Figure 5D shows that the NFS method can suppress the howling well, but it only starts to work after the howling is heard and detected. The spectrogram obtained with the low-complexity howling suppression method provided by the present invention, shown in Figure 5E, does not show an obvious increase in acoustic energy at the problematic frequencies, meaning that the method provided can successfully suppress the howling feedback to a large extent and perform best among these methods.

[0035] For portable karaoke machines, people always want to enjoy it for a long time, but still expect good sound quality, such as less feedback problems at high volume. In the present invention, a low-complexity feedback suppression method is provided that adopts an IIR filter structure to reduce power consumption and system delay time. Nonlinear algorithms such as frequency shifting are also combined with the microphone beamforming method to further suppress feedback.

[0036] The low-complexity feedback suppression method and system provided in the present invention is suitable for applications where the system includes both a loudspeaker and a microphone, with the condition that their relative positions are fixed, and the loudspeaker reproduces the input signal of the microphone in real time, such as, but not limited to, portable karaoke machines, built-in speakers, conference systems, etc.

[0037] As used in this application, an element or step preceded by the word "a" or "an" in the singular is to be understood as not excluding a plurality of such elements or steps, unless the exclusion is expressly stated. Furthermore, references to "one embodiment" or "one example" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. The terms "first," "second," and "third," etc. are used merely as labels and are not intended to impose numerical requirements or a particular positional order on their objects.

[0038] Although exemplary embodiments have been described above, it is not intended that these embodiments describe all possible forms of the present invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the present invention. In addition, features of various implementations can be combined to form further embodiments of the present invention.

Claims

1. 1. A low-complexity feedback suppression method for a portable karaoke system, comprising: capturing, by at least one microphone, an input signal including a source signal and acoustic feedback; in an electrical acoustic path, compressing and equalizing said input signal and then amplifying it before providing it to an output signal; reproducing, by a loudspeaker, said output signal for propagation through an environment; Including, The method includes estimating the acoustic feedback by at least one infinite impulse response (IIR) filter, thereby canceling the acoustic feedback from the input signal; modeling an environmental transfer function with said at least one IIR filter; decorrelating the output signal from the input signal by frequency shifting the input signal; The low-complexity howling suppression method further comprises:

2. The method of claim 1 , wherein the acoustic feedback comprises feedback generated in a closed signal loop caused by acoustic coupling between the loudspeaker and the at least one microphone.

3. The method of claim 1 , wherein the relative positions of the at least one microphone and the loudspeaker are fixed.

4. The method of claim 1 , wherein modeling the environmental transfer function includes measuring and estimating it offline and approximating it.

5. The method of claim 4 , wherein approximating the environmental transfer function is performed by a multi-band IIR filter.

6. The method of claim 1 , further comprising arranging the at least one microphone with different directionality as a microphone array for beamforming.

7. The method of claim 6 , wherein the microphone array forms a cardioid directional pattern.

8. 1. A portable karaoke system with low complexity feedback suppression, comprising: at least one microphone for capturing an input signal including a source signal and acoustic feedback propagating through the environment; an electroacoustic path for compressing and equalizing said input signal and then amplifying it before providing an output signal; a loudspeaker for reproducing said output signal; Equipped with the system further comprising at least one infinite impulse response (IIR) filter for estimating the acoustic feedback and thereby cancelling the acoustic feedback from the input signal; the at least one IIR filter further models an environmental transfer function; A portable karaoke system that decorrelates the output signal from the input signal by frequency shifting the input signal.

9. The system of claim 8 , wherein the acoustic feedback comprises feedback generated in a closed signal loop caused by acoustic coupling between the loudspeaker and the at least one microphone.

10. The system of claim 8 , wherein the relative positions of the at least one microphone and the loudspeaker are fixed.

11. The system of claim 8 , wherein the at least one IIR filter further measures and estimates the environmental transfer function offline and approximates it.

12. The system of claim 11 , wherein the environmental transfer function can be approximated by a multi-band IIR filter.

13. The system of claim 8 , wherein the at least one microphone is further arranged with different directivities as a microphone array for beamforming.

14. The system of claim 13 , wherein the microphone array forms a cardioid directional pattern.

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