Current Limiting Device for Driving a Loudspeaker

Abstract

A method for use with an acoustic system (referred to as a plant in control theory) (125) including a loudspeaker set (120), the method comprising obtaining an input audio sample (r n ) and a measured current (m n-d ) drawn by the loudspeaker set, and for a current time step, using a state space model of the loudspeaker set to generate a state vector (x n ) and a model-based estimated current (y n ), generating a predicted current (y n ) for a next time step based on the state vector (x e,n+1 ), generating a replacement audio sample (u n ) based on the state vector (x L,n ) for the current time step, generating a feedback signal (f n-d ) that contributes to the generation of the state vector (x n-d ) for a next time step based on the measured current (m n+1 ) and a time-aligned model-based estimated current (y n ), and generating an output audio sample (u n ) for the current time step, wherein when the predicted current (y e,n+1 ) is higher in amplitude than a threshold (I max ), the output audio sample (u n ) is either the input audio sample (r n ) or the replacement audio sample (u L,n ) for the current time step.

Description

Technical Field

[0001] Various exemplary embodiments generally relate to current limiting devices and related methods for driving a loudspeaker.

Background Art

[0002] Most audio power amplifiers have a maximum output current limit beyond which the output stage may be damaged.

[0003] A common solution for linear amplifiers with push - pull output stages is to have an additional control loop that measures the output current in the emitter or source resistor of the output stage of the linear amplifier, disables the normal control signal, and controls the output device to a constant maximum current.

[0004] In a PWM (Pulse Width Modulation) amplifier or inverter, a protection circuit may be implemented within the driver IC (Integrated Circuit) that controls the switching output device. The output current is detected in various ways. When the threshold of the output current is reached, the driver IC is configured to turn off the output stage completely and restart after a recovery time. During that time, there is no output audio signal sent to the loudspeaker, which is unacceptable during normal operation of an audible amplifier.

[0005] To prevent this, an additional control loop with fast current measurement may be used within the driver IC to perform per - pulse current limiting to obtain a constant maximum output current.

[0006] There appears to be a need for an improved solution for limiting the current drawn by a loudspeaker.

Summary of the Invention

[0007] The scope of protection is indicated by the independent claims. Embodiments, examples, and features described herein that do not fall within the scope of protection, if any, should be construed as useful examples for understanding the various embodiments or examples that fall within the scope of protection.

[0008] According to a first aspect, a device for use with an acoustic system (referred to as a plant in control theory) including a loudspeaker set is disclosed. The device is configured to receive an input audio sample and a measured current drawn by the loudspeaker set and generate an output audio sample for a current time step. The device includes a modeling device configured to generate, for the current time step, a state vector of the current drawn by the loudspeaker set and a model-based estimated current from the output audio sample using a state-space model of the loudspeaker set, a prediction device configured to generate a predicted current for a next time step based on the state vector, a limiting device configured to generate, for the current time step, a replacement audio sample that is a replacement audio sample based on the state vector and in which the amplitude of the current drawn by the loudspeaker is limited to a maximum value, and a state feedback controller configured to generate a feedback signal for contribution to the generation of the state vector for a next time step, the feedback signal being based on a comparison between the measured current and a time-aligned model-based estimated current. When the amplitude of the predicted current is higher than a threshold value, the output audio sample is either the input audio sample or the replacement audio sample for the current time step. The prediction device may be configured to generate a predicted current based on one or more input audio samples.

[0009]

[0010] ​The prediction device may be configured to generate a predicted current based on an estimated audio sample for the next time step or an input audio sample for the next time step.

[0011] The limiting device may be configured to generate a replacement audio sample based on a model derived from a state space model.

[0012] The limiting device may be configured to generate a replacement audio sample based on a threshold corresponding to a maximum current.

[0013] The replacement audio sample may be generated such that the amplitude of the predicted current equals the threshold.

[0014] The replacement audio sample may be generated based on the sign of the predicted current.

[0015] The replacement audio sample may be generated based on an output sample for the previous time step.

[0016] According to a second aspect, a method for use with an acoustic system (referred to as a plant in control theory) including a loudspeaker set is disclosed. The method includes obtaining an input audio sample and a measured current drawn by the loudspeaker set, generating an output audio sample for a current time step, using a state space model of the loudspeaker set for the current time step to generate a state vector of the current drawn by the loudspeaker set and a model-based estimated current from the output audio sample, generating a predicted current for a next time step based on the state vector, generating a replacement audio sample for the current time step based on the state vector, the replacement audio sample being such that the amplitude of the current drawn by the loudspeaker set is limited to a maximum value, generating a feedback signal for the next time step to be supplied to the state space model to contribute to the generation of the state vector, the feedback signal being based on a comparison between the measured current and the time-integrated model-based estimated current, and when the amplitude of the predicted current is higher than a threshold value, the output audio sample is either the input audio sample or the replacement audio sample for the current time step.

[0017] According to another aspect, a computer program is disclosed. The computer program includes computer-executable instructions that, when executed by at least one processor, cause a device to perform the method according to the second aspect.

[0018] According to a third aspect, a device for use with an acoustic system (referred to as a plant in control theory) including a loudspeaker set is disclosed. The device obtains an input audio sample and a measured current drawn by the loudspeaker set, generates an output audio sample for a current time step, and for the current time step, using a state space model of the loudspeaker set, generates a state vector of the current drawn by the loudspeaker set and a model-based estimated current from the output audio sample, and generates a predicted current for a next time step based on the state vector. For the current time step, generates a replacement audio sample based on the state vector, where the replacement audio sample is such that the amplitude of the current drawn by the loudspeaker set is limited to a maximum value, and for the next time step, generates a feedback signal supplied to the state space model to contribute to the generation of the state vector, where the feedback signal is based on a comparison between the measured current and the time-integrated model-based estimated current, and includes a signal processing means (e.g., a signal processor) for performing a method including: when the amplitude of the predicted current is higher than a threshold value, the output audio sample is either the input audio sample or the replacement audio sample for the current time step.

[0019] The signal processing means may comprise at least one processor and at least one memory including computer program instructions, and the at least one memory and the computer program instructions are configured to cause the device to perform one or more or all steps of the method using the at least one processor. The signal processing means may comprise a circuit configured to cause the device to perform at least one or more or all steps of the method. The signal processing means may comprise a digital signal processor configured to cause the device to perform one or more or all steps of the method.

[0020] The signal processing means may include a modeling device, a prediction device, a restriction device and a state feedback controller defined for the device according to the first aspect.

[0021] According to a fourth aspect, a system including a device according to the first aspect or the third aspect is disclosed. The system includes a database configured to store model coefficients of a state space model for several loudspeaker sets, and means for loading the model coefficients corresponding to a loudspeaker set. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Exemplary embodiments will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and thus are not limiting of the present disclosure. It should be noted that these drawings are intended to show various aspects of the devices, methods, and structures used in the exemplary embodiments described herein. The use of like or identical reference numbers in the various drawings is intended to indicate the presence of like or identical elements or features.

[0023]

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[0024] Next, various exemplary embodiments will be described in more detail with reference to the accompanying drawings that show some exemplary embodiments. However, the specific structural and / or functional details disclosed herein are merely representative examples for the purpose of describing the exemplary embodiments. Accordingly, these embodiments are shown as exemplary examples in the drawings and are described in detail herein to provide a complete understanding of the various aspects. However, it will be understood by those skilled in the art that the exemplary embodiments are capable of various modifications and alternative forms and can be implemented without all of the specific details. In some cases, the systems and processes are shown in block diagrams to avoid obscuring the exemplary embodiments with unnecessary details. In other cases, well-known processes, structures, and techniques may be shown without unnecessary details to avoid obscuring the embodiments of the examples.

[0025] A voice system including a current limiting device will be described in detail. The current limiting device executes a prediction algorithm that predicts the current drawn by a loudspeaker set (e.g., including one or more loudspeakers) based on the model of the loudspeaker set. A replacement output voltage (corresponding to the sample value generated by the limiting device, also referred to herein as a replacement audio sample) is generated such that the amplitude of the drawn current does not exceed a specified threshold. The replacement output voltage (i.e., the replacement audio sample) is output to the plant instead of the output voltage of the sound source when the amplitude of the predicted current is higher than the specified threshold. The current drawn by the loudspeaker is limited to a maximum value, and the replacement output voltage is determined based on the limited current.

[0026] FIG. 1 shows a block diagram of a current limiting device 100 according to an embodiment. The current limiting device 100 is connected to a sound source 110, and its output is connected via a selector 160 to an acoustic system 125 including a loudspeaker set 120 for reproducing an analog audio signal. This acoustic system 125 is referred to as a plant in control theory.

[0027] The acoustic system or plant 125 includes, following a digital-to-analog converter (DAC) and an amplifier stage 119, a loudspeaker set 120, a current measurement device 121 that generates a measured current, and an analog-to-digital converter (ADC) that supplies the measured current to the current limiting device 100, and may itself include a signal chain for. The loudspeaker set 120 includes a horn. The loudspeaker set 120 may include one or more loudspeakers, for example, the same type of loudspeakers connected in parallel that can be modeled using a single model. The loudspeaker set 120 may alternately include at least one low-frequency loudspeaker connected to the output of the amplifier by a passive cross-over network and at least one high-frequency loudspeaker (for example, a woofer and a tweeter). For a better understanding of the time alignment aspect, the schematic diagram of FIG. 1 includes a delay element 122 that represents the delay introduced by a digital-to-analog converter (DAC) and an analog-to-digital converter (ADC) here.

[0028] In the embodiment of FIG. 1, the current limiting device 100 includes means (for example, software means and / or hardware means) configured to implement a loudspeaker set model (modeling device 130), a limiter (limiting device 140), a prediction algorithm (prediction device 150), a selector 160, and a related threshold determination function (threshold determination device 155). The current limiting device 100 may further include a delay element 132, an adder 133, and a state feedback controller 135 whose output is connected to the modeling device 130 within a feedback loop. The delay signal y from the delay element 132 n-d is added to the current measurement value m n-d with a negative sign.

[0029] The sound source 110 generates an audio signal that can be an analog audio signal or a digital audio signal. When the audio signal is an analog audio signal, this analog audio signal is converted (for example, by an analog-to-digital converter not shown) into digital samples called input audio samples r n , where n = 1 to N. When the audio signal is a digital audio signal, here it is assumed to include the input audio samples r n , where n = 1 to N.

[0030] The current limiting device 100 receives input audio samples r n , n = 1 to N as an input signal from the sound source 110, and generates output audio samples u n , n = 1 to N, which are converted into analog signals to be reproduced by the loudspeaker set 120 (e.g., by a digital-to-analog converter included in the amplification stage represented as 119). The input audio sample r n represents the output voltage at the output of the sound source. The output audio sample represents the output voltage applied into the plant 125 to drive the loudspeaker set 120 such that the loudspeaker set 120 draws a current, which is referred to herein as the drawn current.

[0031] The current limiting device 100 may be implemented by a signal processing circuit configured to perform one or more or all of the steps and / or functions disclosed herein for the current limiting device 100. The current limiting device 100 may include or be subdivided into one or more devices and / or signal processing circuits.

[0032] The signal processing circuit may include at least one DSP (Digital Signal Processing) circuit. The signal processing circuit may include at least one processor and at least one memory including computer program code, and the at least one memory and the computer program code are configured to cause the device to perform one or more or all of the steps and / or functions disclosed herein for the current limiting device 100, in conjunction with the at least one processor.

[0033] In the solution described herein, a prediction algorithm is used to predict and limit the current drawn by the loudspeaker set 120, using a replacement output voltage that is converted to a voltage, amplified by the amplification stage 119, and applied to the loudspeaker set 120, instead of the output signal at the output of the sound source 110.

[0034] ​The prediction algorithm is based on a loudspeaker set model that is executed by a modeling device 130 connected to the output of the sound source 110 via a selector 160. The loudspeaker set model is a model of the driven loudspeaker set 120. A state space model corresponding to the electrical equivalent circuit of the loudspeaker set may be used as the loudspeaker set model, for example, as described in detail.

[0035] The prediction device 150 is configured to implement a prediction algorithm to generate a predicted current y e,n+1 The prediction device 150 receives, as inputs, one or more input audio samples r n where n = 1 to N, and the index n represents, for example, a time step index with respect to a clock signal. The prediction algorithm may use available input audio samples (e.g., the current sample r n and the previous sample r n-1 ). The prediction algorithm may use the next input audio sample if available, or at least one predicted sample r n+1 for the next time step obtained from one or more input audio samples. The predicted r n+1 samples may be generated, for example, by using two or more input audio samples (e.g., r n-1 and r n , n = 1 to N). The prediction device 150 receives the state vector x n from the modeling device 130 as an input and generates a predicted current y e,n+1 for the next time step at a given time step.

[0036] The state space model is synchronized with the plant 125 by using the feedback error e n-d supplied to the state feedback controller 135 of the state space model 130. The feedback error e n-d is generated based on the measured current (m n-d ) and the time - aligned model - based estimated current (y n-d ). The feedback error en-d may be generated as the difference between the measured current (m n-d ) and the model-based estimated current (y n-d ) that is time-aligned. The state feedback controller 135 is configured to generate a feedback signal (f n ) that contributes to the generation of the state vector for the next time step. This feedback signal may be a feedback vector that is added to the state vector at the current time step to generate the state vector for the next time step based on the state space model.

[0037] The limiting device 140 is configured to implement a limiter function. The limiting device 140 receives the state vector x n from the modeling device 130 and generates replacement audio samples u L,n , n = 1 to N, based on a derived model obtained from a mathematical transformation of the loudspeaker set model. The coefficients of the derived model are based on the coefficients of the loudspeaker set model. The replacement audio sample u L,n represents a replacement audio signal that is different from the input audio signal (i.e., the input audio sample r n ) that represents the audio content to be reproduced and may be used in the replacement of the corresponding input audio sample r n to avoid the amplitude of the current drawn by the loudspeaker set 120 from exceeding a threshold.

[0038] Also, the amplitude of the current drawn by the loudspeaker set 120 to which the replacement output sample u L,n is applied is lower than the amplitude of the current drawn by the loudspeaker set 120 for the corresponding input audio sample r n , provided that it is applied to the amplifier stage 119. As used herein, the term "magnitude" refers to the absolute value of the instantaneous amplitude of a time-varying signal (e.g., a current signal). By convention, the amplitude is always a positive or null value.

[0039] The replacement audio signal uL,n keeps the amplitude of the pull-in current y at the maximum value l until the input audio signal again results in a lower pull-in current. The replacement audio signal is also supplied to the amplifier stage 119, where it is converted into a voltage for driving the loudspeaker set 120, so that the current drawn by the loudspeaker set is also limited to the maximum value I within the audio system or plant 125. n of the pull-in current y max Note that the sign of the pull-in current y can be positive or negative so that the pull-in current y can be maintained at + / -I. max is limited to. The pull-in current y n is limited to. The pull-in current y n is maintained at + / -I max be maintained at.

[0040] The threshold determination device 155 receives the predicted current y e,n+1 and compares its amplitude (or absolute value) with a threshold I max (i.e., the maximum value) to generate a control signal for the selector 160. At each time step n, in response to the control signal generated based on the predicted current y e,n+1 , the selector 160 sends out u n as the output of the current limiting device 100, where u n is either - the replacement audio sample u e,n+1 received from the limiting device 140 when the amplitude of the predicted current y max is higher than the current threshold I L,n , or - or the input audio sample r e,n+1 received from the sound source when the amplitude of the predicted current y max is lower than the threshold I n . When the amplitude of the predicted current y e,n+1 is equal to the threshold I max , either the replacement audio sample u L,n or the input audio sample r n may be used.

[0041] Based on the above characteristics, the current limiting device 100 can predict an increase in the amplitude of the drawn current exceeding the maximum value and correct the output signal u supplied to the plant before reaching this maximum value. n It is possible to correct.

[0042] The reason for using prediction is (in contrast to simply using the measured current m n and directly supplying it to the limiting algorithm), that it takes time (one or more time steps) for the sampling of the drawn current and its transfer to the current limiting device 100, and such a delay limits the ability to react in a timely manner. Furthermore, the state space model allows predicting the next sample in advance (even when using block processing as described herein), which is at least one sample before the current sample.

[0043] The state space model is a fixed linear model. Even if this model slightly differs from the loudspeaker set in the plant, the feedback signal enables the model state to continue to be synchronized with the actual state of the loudspeaker set.

[0044] Furthermore, in this prediction algorithm, a simpler hardware protection circuit (for example, a protection circuit that simply switches off and restarts the audio power amplifier) may be used, and it is acceptable because the current limiting device can prevent the triggering of this protection circuit during normal operation.

[0045] Figure 2A shows an example of the equivalent electrical circuit of a woofer loudspeaker in a double-vented box. In this equivalent electrical circuit, the loudspeaker is driven by a voltage source. For more complex loudspeakers with a crossover network and other drivers, a more complex equivalent electrical circuit may be used.

[0046] Figure 2B shows the derived model of the equivalent electrical circuit of a woofer loudspeaker in a double-vented box. In this equivalent electrical circuit, the loudspeaker is driven by a current source.

[0047] The amplitude of this current source is set to + / -I corresponding to the target maximum value for the amplitude of the drawn current y n When this is done, the output voltage u max is obtained at the drive node of the current source. The output voltage u n and the drawn current y n The relationship between and is such that the output voltage u n enables obtaining the target maximum value for the amplitude of the drawn current. The output voltage u n is given by the loudspeaker set model such that it can be determined from the loudspeaker set model and the state vector x n of the loudspeaker set model.

[0048] Figure 3 shows a state space model that can be used as a loudspeaker set model for either a single loudspeaker or a loudspeaker set within a plant. The state vector is x n and the coefficients of the model are contained in the matrices and / or vectors A, B, C, and D. The size of the state vector x n and likewise the size of the matrices and / or vectors A, B, C, and D may depend on the equivalent electrical circuit selected. The state vector x n may include all the currents of the inductors and the voltages of the capacitors of the equivalent electrical circuit of the loudspeaker set model.

[0049] In the example of Figure 3, it is as follows: -u n represents the input sample (e.g., input voltage), and also -y n represents the output sample (e.g., model-based estimated current).

[0050] The audio input r n is copied to the input u n of the device as long as no current limit occurs. The following calculations are performed at each time step: · Output y: y n =C·x n +D·u n · Next state x: x n+1 =A·x n+B·u n · The next input r: r e,n+1 =2·r n -r n-1 (r e,n+1 's prediction is based on linear extrapolation in this example) · The next output y: y e,n+1 =C·(A·x n +B·r n )+D·r e、n+1 · |y e、n+1 |>i max In the case of: y e,n+1 =C·(A·x n +B·u L 、n )+D·u L,n+1 =±i max · Smooth transition: u L,n+1 =(1+λ)·u L,n -λ·u n-1 (λ may be set to 0.5). · Solution: u L,n =(C·B+(1+λ)·D) -1 ·(±i max -C·A·x n +λ·D·u n-1 )

[0051] Note that the sign of ±i max is the same as the sign of y e,n+1 . It should be noted that the index "e" indicates that the related parameter is the estimated value at the next time step n+1.

[0052] To improve the accuracy of the loudspeaker set model, the measured value m n-d of the current drawn by the loudspeaker set is available, and the current y n-d generated by the loudspeaker set model is compared to generate the feedback error e n-d . A closed-loop control model may be used. The feedback error may be obtained after a delay d represented by the number of time steps. This delay may correspond to several time steps, and then the measured current m n-dis obtained: The corresponding delay line for the d time step is then applied to the current y n to yield a time - aligned model - based estimated current y n-d and a feedback error e n-d is generated. The vector state x n of the loudspeaker set model is updated based on the feedback error e n-d This closed loop is illustrated in the block diagram of FIG. 1 by the elements represented by the dotted lines within the current - limiting device. Thus, the state - space model is synchronized with the plant 125 and the loudspeaker set.

[0053] The measured current m n is obtained, for example, by a current probe, sampled by an analog - to - digital converter (ADC) (121), and provided to the current - limiting device. The prediction algorithm enables timely reaction to possible future currents. The state - space model enables prediction of the next sample prior in time (one time step prior in time), and when this state - space model is used in a closed loop, the measured values are used to keep the model state variables synchronized with the actual loudspeaker set (see FIG. 1).

[0054] Returning to FIG. 1, the audio system 190 includes - a sound source 110, - a current - limiting device 100 configured to implement a loudspeaker set model and a prediction algorithm that generates a predicted current for the next time step of a given loudspeaker set based on the loudspeaker set model, - an acoustic system 125 (e.g., a plant) including a processing chain having an amplifier (119) followed by a loudspeaker set 120 including one or more loudspeakers, - a current probe (121) that samples the current at the output of the amplifier, - (when not yet in digital audio signal r n ) the input signal r n , mn An analog-to-digital converter (not shown) that converts n to a digital format, including a current limiting device 100 and an output signal u n An analog-to-digital converter (not shown) that can be processed by a digital-to-analog converter for converting n to an analog format, and - A database (not shown) for storing pre-calculated coefficients (pre-calculated model matrix) for a list of well-known loudspeaker sets may be included.

[0055] In one or more embodiments, a loudspeaker set 120 connected to an amplifier (119) may be detected. This can be done automatically at runtime. For this purpose, the audio system 190 may include means for detecting a loudspeaker set connected to an amplifier 119 within the acoustic system (125). The means for detecting the loudspeaker set may perform the detection of the loudspeaker set based on a measured value of the impedance of the connected loudspeaker set.

[0056] The current limiting device 100 may include means for loading model coefficients corresponding to the detected loudspeaker set. The equivalent electrical circuit itself may also be selected for the detected loudspeaker set and used to calculate the coefficients of the loudspeaker set model to be implemented by the current limiting device 100. The loading of the model coefficients from the database may be performed when the audio system 190 is switched on or in response to a change in the loudspeaker.

[0057] FIG. 4 shows a block diagram of a current limiting device 500 according to an embodiment. FIG. 4 shows how the state space model of FIG. 3 can be used within a closed loop having a plant 525 within the current limiting device 500 connected to a sound source 510 and a plant 525.

[0058] In the embodiment of FIG. 4, the current limiting device 500 includes a device configured to implement a loudspeaker set model (modeling device 530), a limiter (limiting device 540), a prediction algorithm (prediction device 550), a selector 560, and a threshold determination (threshold determination device 555), respectively. The current limiting device 500 may further include a delay element 532, an adder 533, and a state feedback controller 535 whose output is connected to the modeling device 530, within the feedback loop.

[0059] The description made with reference to FIG. 1 applies to the corresponding elements of FIG. 4. Further calculation details are provided here regarding the functions of the modeling device 530, the limiting device 540, the prediction device 550, and the threshold determination device 555.

[0060] The current limiting device 500 operates as follows.

[0061] The prediction device 550 receives at least one input audio sample r n and a state vector x n Based on the coefficients of the loudspeaker set model, the prediction device 550 generates an estimated state vector x n from the input audio sample r n and the state vector x e,n+1 X e,n+1 =A·x n +B·r n Here, "·" represents a matrix product.

[0062] The prediction device 550 generates an estimated audio sample r e,n+1 from one or more input audio samples. r e,n+1 =2·r n -r n-1

[0063] The prediction device 550 generates a predicted current y e,n+1 from the estimated state vector x e,n+1 and the estimated audio sample re,n+1 Generate y e,n+1 = C·x e,n+1 + D·r e,n+1

[0064] The limiting device 540 receives the output audio sample u n and the state vector x n The limiting device 540 is configured to generate a replacement audio sample u from the sign of the current state vector x of the loudspeaker set and the predicted current y n and the predicted current y e,n+1 The replacement audio sample u is such that the amplitude of the predicted current equals the threshold I L,n : L,n The predicted current amplitude equals the threshold I max : U L,n = M·(I max ·sign{y e,n+1}- C·A·x n + λ·D·u n-1 ) The sign function can be defined as follows: [Number] Depending on the hardware and / or software platform, the function sign{0} may return 0 or 1. The methods described herein function with both options Here, the matrix M = (C·B + (1 + λ)·D) -1 where λ is a scalar such that 0 ≤ λ ≤ 1. The scalar λ is used to control the control feedback strength and voltage smoothing for the previous output sample u n-1 If λ = 0, the previous input sample u is not considered. A good trade-off between voltage smoothing and control feedback strength is achieved with λ = 0.5 n-1 :

[0065] The selector 560 selects either the replacement audio sample U L,n or the input audio sample r n to produce the output sample u nconfigured to generate.

[0066] The threshold determination device 555 compares the predicted current y e,n+1 with a threshold I max and, when the predicted current y e,n+1 is higher than the threshold I max (i.e., |y e,n+1 | > I max ), configures the selector 560 to control the output sample u n to be replaced by the replacement audio sample u L,n . When the predicted current y e,n+1 is lower than the threshold I max , the output sample u n is equal to the input audio sample r n . In the case of equality, either the replacement audio sample u L,n or the input audio sample r n may be used.

[0067] The modeling device 530 is configured to update the state vector x n+1 and calculate the current y n drawn by the loudspeaker set. The drawn current is calculated as follows: y n = C·x n + D·u n

[0068] In the feedback loop, the feedback error may be calculated as follows: e n-d = m n-d - y n-d where m n-d is the measured current at time step n - d, y n-d is the time-aligned version of the model-based estimated current y n at time step n - d, and d is the measurement delay at the time step.

[0069] Finally, the state vector is updated for the next time step by considering the feedback signal generated by the state feedback controller (here, the feedback vector L·e n-d ): The next state vector x n+1 may be calculated as follows: X n+1 =A·x n +B·u n +L·e n-d

[0070] The coefficients of the vectors I matrices A, B, C, D, M, L may be pre-calculated for each loudspeaker set model. The equivalent electrical circuit shown by FIG. 2B is represented by the matrix M. This matrix M corresponds to the inverse matrix that enables calculating the replacement input sample u n based on the state vector x max , the threshold I n-1 , the previous audio sample u e,n+1 , and the predicted current y L,n .

[0071] Note that in this embodiment, the equivalent electrical circuit of FIG. 2B is used. When this current source is set to ±I max corresponding to the threshold, the output voltage u n is obtained at the driving node of the current source. Next, this voltage u n can be used as the input voltage to the loudspeaker set model 130 or 530 and can also be applied to the plants 125, 525 including the loudspeaker sets 120, 520.

[0072] The above method aims to limit the current drawn using one-time-step look-ahead. By estimating the predicted current y e,n+1 and then calculating the output voltage u n , rapid voltage changes and unwanted frequency content are reduced.

[0073] FIG. 5 shows curves representing the variation of the amplitude (FIG. 5A) and phase (FIG. 5B) of admittance over frequency for a typical loudspeaker set according to an embodiment. Each dotted curve corresponds to a curve obtained based on current measurement values and voltage measurement values respectively, and each solid curve corresponds to a curve obtained based on current values and voltage values generated by a model of the loudspeaker set respectively. The minimum value 51 of the curve appears at 28 Hz, which corresponds to a situation with low admittance and a low current is expected when a voltage is applied. The maximum peak 52 of the curve appears at 47 Hz, which corresponds to a situation with high admittance and a high current is expected when a voltage is applied. By comparing the dotted curves with the solid curves in each figure, both the phase and amplitude of the admittance appear to match exactly by the model.

[0074] FIG. 6 shows a burst signal having a sine wave of 28 Hz. In FIG. 6A, the input voltage corresponding to the input sample (r n ) from the sound source is represented by a solid line, while the replacement output voltage (u L,n ) is represented by a dotted line: this replacement output voltage replaces the input voltage and is generated by the limiter devices 140, 540 to generate the voltage (u n ) supplied to the plant, which is also the voltage at the input of the loudspeaker set model 130. FIG. 6B represents the output current (y n ) at the output of the loudspeaker set models 130, 530. FIG. 6B shows the effect of the current limit applied by the current limiting device. By replacing the input voltage with the replacement output voltage during the first peak 61 in FIG. 6A, the output current is limited and clipped to I max = 24 A during the same period as shown by the peak 62 in FIG. 6B. Since the signal is at 28 Hz, the admittance is low and it is in a situation where a low current is expected, but this is a transient state where current limiting is required and clipping is observed to occur.

[0075] Figure 7 shows the same curve as in Figure 6 but has a 47 Hz sine wave with high admittance and high current expected. However, here, during switch - on (transient state), there is little voltage limiting for the first voltage peaks 71, 72, but clipping to I max = 24 A is observed to occur between the corresponding current peaks 75, 76. Strong voltage limiting occurs for the next voltage peaks 73, 74, and clipping to I max = 24 A also occurs for the corresponding current peaks 77, 78.

[0076] In an embodiment, the device is configured to receive an input audio sample and a measured current drawn by a loudspeaker set. The device includes a modeling device configured to generate a state vector and a model - based estimated current for the current time step using a state - space model of the loudspeaker set, a prediction device configured to generate a predicted current for the next time step based on the state vector, a limiting device configured to generate a limited audio sample for the current time step based on the state vector, and a state feedback controller configured to generate a feedback signal for the generation of the state vector for the next time step based on the measured current and the time - aligned model - based estimated current. The device is configured to generate an output audio sample for the current time step, and the output audio sample is either the input audio sample for the current time step or the limited audio sample if the amplitude of the predicted current is higher than a threshold.

[0077] Any functions, engines, block diagrams, flowcharts, state transition diagrams, flow diagrams, and / or data structures described herein should be understood by those skilled in the art to represent conceptual diagrams of exemplary circuits embodying the principles of the present invention. Similarly, any flowchart, flow diagram, state transition diagram, pseudocode, etc. is substantially represented in a computer-readable medium, and thus, whether or not a computer or processing device is explicitly shown, it should be understood to represent various processes that can be executed by such a computer or processing device.

[0078] A flowchart may describe operations as sequential processes, but many of the operations may be executed in parallel, concurrently, or simultaneously. Also, some operations may be omitted, combined, or executed in a different order. A process may end when its operations are completed, but may also have additional steps not disclosed in the figure or description. A process may correspond to a method, function, procedure, subroutine, subprogram, etc. When a process corresponds to a function, its end may also correspond to the return of the function to the calling function or main function.

[0079] Each of the described functions, engines, blocks, steps described herein can be executed in hardware, software, firmware, middleware, microcode, or any suitable combination thereof.

[0080] In this description, "means for performing a function" or "machine The expression "means configured to perform a function" may correspondingly refer to one or more functional blocks comprising a circuit adapted or configured to perform this function. The block may perform this function by itself or may cooperate and / or communicate with one or more other blocks to perform this function. "Means" may correspond to or be implemented as "one or more modules", "one or more devices", "one or more units", etc., and may include at least one processor and at least one memory storing instructions configured to cause the processor to perform functions related to a target device / target system.

[0081] The current limiting device may be implemented by software and / or hardware.

[0082] When implemented in software, the current limiting device may be implemented by a circuit (e.g., one or more circuits). The following types of circuits may be used: digital signal processing (DSP) hardware, a processor or microprocessor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc. The circuit may be, for example, programmable logic that executes hardware, software, or firmware, a programmable processor, and / or any combination of these (e.g., a processor, a control unit / entity, a controller) that executes instructions or software and controls the transmission and reception of signals, and a memory for storing data and / or instructions, or may include these.

[0083] ​When implemented in software, firmware, middleware, or microcode, the instructions for performing the required tasks may be stored on a computer-readable medium that may or may not be included in the target device or system. The instructions may be transmitted via the computer-readable medium and loaded into the target device or system. The instructions are configured to cause the target device / target system to perform one or more of the functions disclosed herein. For example, as described above, according to one or more embodiments, at least one memory may contain or store the instructions, and at least one memory and the instructions may be configured to cause the target device / target system to perform one or more functions using at least one processor. Note that the processor, memory, and instructions act as means for providing or causing the execution of one or more of the functions disclosed herein by the target device / target system. For example, as described above, according to one or more embodiments, at least one memory may contain or store the instructions, and at least one memory and the instructions may be configured to cause the target device / target system to perform one or more functions using at least one processor. Note that the processor, memory, and instructions act as means for providing or causing the execution of one or more of the functions disclosed herein by the target device / target system.

[0084] The instructions may correspond to computer program instructions, computer program code, and may include one or more code segments. The code segments may represent any combination of processing procedures, functions, subprograms, programs, routines, subroutines, modules, software packages, classes, or instructions, data structures, or program states.

[0085] When provided by a processor, the functionality may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors that may share some parts. The term "processor" refers to executing software It should not be construed as exclusively referring to hardware that is capable, and may implicitly include one or more processing circuits, whether programmable or not. Processing circuits may correspond to a digital signal processor (DSP), network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), system-on-chip (SoC), central processing unit (CPU), processing unit, arithmetic logic unit (ALU), programmable logic unit (PLU ), processing core, programmable logic, microprocessor, controller, microcontroller, microcomputer, or any device capable of responding to and / or executing instructions according to a defined method and / or defined logic. Conventional or custom other hardware may also be included. The processor may be configured to execute instructions adapted to cause execution by a target device or system of one or more functions disclosed herein for the relevant device or system.

[0086] ​A computer-readable medium or computer-readable storage medium may be any storage medium suitable for storing instructions readable by a computer or processor. More generally, a computer-readable medium may be any storage medium capable of storing and / or containing and / or transporting instructions and / or data. A computer-readable medium may be a portable storage medium or a fixed storage medium. A computer-readable medium may include one or more storage devices such as a permanent mass storage device, a magnetic storage medium, an optical storage medium, a digital storage disk (CD-ROM, DVD, Blue Ray, etc.), a USB key or dongle or peripheral device, a memory card, a random access memory (RAM), a read only memory (ROM), a core memory, a flash memory, or any other non-volatile storage device.

[0087] A memory suitable for storing instructions may be a random access memory (RAM), a read only memory (ROM), and / or a permanent mass storage device such as a disk drive, a memory card, a random access memory (RAM), a read only memory (ROM), a core memory, a flash memory, or any other non-volatile storage device.

[0088] The terms first, second, etc. may be used herein to describe various elements, but these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the present disclosure, the first element may be referred to as the second element, and similarly, the second element may be referred to as the first element. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0089] When an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements. Other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between" versus "directly between", "adjacent" versus "directly adjacent", etc.). )", "adjacent" versus "directly adjacent", etc.).

[0090] The terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", and / or "including", as used herein, specify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It will be further understood that

[0091] To provide a thorough understanding of some embodiments, specific details are provided in the following description. However, it will be understood by those skilled in the art that exemplary embodiments may be practiced without these specific details. For example, the system may be shown in block diagrams so as not to obscure the embodiments with unnecessary detail. In other instances, well-known processes, structures, and techniques may be shown without unnecessary detail to avoid obscuring the embodiments.

[0092] Advantages, other benefits, and solutions to problems have been described above with respect to specific embodiments of the invention. However, advantages, benefits, solutions to problems, and any element(s) that may cause or result in such advantages, benefits, or solutions, or that may make such advantages, benefits, or solutions more pronounced, should not be construed as important, necessary, or essential features or elements of the invention.

Claims

1. A device (100, 500) for use with a plant (125, 525) including a loudspeaker set, the device receiving an input audio sample (r ｎ ), and a measured current (m ｎ－ｄ ) drawn by the loudspeaker set, and being configured to generate an output audio sample (u ｎ ) for a current time step, the device being - For the current time step, using the state space model of the loudspeaker set, the output audio sample (u ｎ ), the state vector (x ｎ ) of the current drawn by the loudspeaker set and the model-based estimated current (y ｎ ) are generated, a modeling device (130, 530) configured as follows, - Based on the state vector (x ｎ ), a prediction device (150, 550) configured to generate a predicted current (y ｅ，ｎ＋１ ) for the next time step, - For the current time step, a replacement audio sample (u ｎ ), based on the state vector (x Ｌ，ｎ ), wherein the replacement audio sample (U Ｌ，ｎ ) is such that the amplitude of the current drawn by the loudspeaker set is limited to a maximum value, a limiting device (140, 540) configured to generate the replacement audio sample (u Ｌ，ｎ ); - For the next time step, a feedback signal (f ｎ＋１ ) supplied to the state space model to contribute to the generation of the state vector (x ｎ ), wherein the feedback signal (f ｎ ) is based on a comparison between the measured current (m ｎ－ｄ ) and a time-aligned model-based estimated current (y ｎ－ｄ ), and a state feedback controller (135, 235) configured to generate the feedback signal (f ｎ ); and the device (100, 500) wherein when the amplitude of the predicted current (y ｅ，ｎ＋１ ) is higher than a threshold (I ｍａｘ ), the output audio sample (u ｎ ) is either the input audio sample (r ｎ ) or the replacement audio sample (u Ｌ，ｎ ) for the current time step.

2. The prediction device (150, 550) is configured to generate the predicted current (y ｎ , r ｎ－１ ) based on one or more input audio samples (r ｅ，ｎ＋１ ), the device (100, 500) according to claim 1.

3. The prediction device (150, 550) is based on the estimated speech sample (r ｅ，ｎ＋１ ) or the input speech sample (r ｎ＋１ ) for the next time step, and is configured to generate the predicted current (y ｅ，ｎ＋１ ). The device (100, 500) according to claim 1 or 2.

4. The device (100, 500) according to any one of claims 1 to 3, wherein the limiting device (140, 540) is configured to generate the replacement audio sample (u Ｌ，ｎ ) based on a model derived from the state space model (130, 530).

5. The limiting device (140, 540) is configured to generate the replacement audio sample (u Ｌ，ｎ ) based on the threshold value representing the maximum current, for the device (100, 500) according to any one of claims 1 to 4.

6. The replacement audio sample u Ｌ，ｎ is generated such that the amplitude of the predicted current (y ｅ，ｎ＋１ ) is equal to the threshold value (I ｍａｘ ), the device (100, 500) according to any one of claims 1 to 5.

7. the replacement audio sample u Ｌ，ｎ is generated based on the sign of the predicted current (y ｅ，ｎ＋１ ), the device (100, 500) according to any one of claims 1 to 6.

8. the replacement audio sample u Ｌ，ｎ is generated based on the output sample u ｎ－１ for the previous time step, the device (100, 500) according to any one of claims 1 to 7.

9. A method for use with a plant (125, 525) comprising a loudspeaker set (120, 520), the method comprising - Input audio sample (r ｎ ) and the measurement current (m ｎ－ｄ ) drawn by the loudspeaker set, and obtain - Generate an output audio sample (u ｎ ) for the current time step, and - For the current time step, using the state space model of the loudspeaker set, from the output audio sample (u ｎ ), generate the state vector (x ｎ ) of the current drawn by the loudspeaker set and the model-based estimated current (y ｎ ); and - Based on the state vector (x ｎ ), generate a predicted current (y ｅ，ｎ＋１ ) for the next time step, and - For the current time step, a replacement audio sample (u ｎ ), based on the state vector (x Ｌ，ｎ ), where the replacement audio sample (u Ｌ，ｎ ) is such that the amplitude of the current drawn by the loudspeaker set is limited to a maximum value, generating the replacement audio sample (u Ｌ，ｎ ); - For the next time step, a feedback signal (f ｎ＋１ ) supplied to the state space model to contribute to the generation of the state vector (x ｎ ), wherein the feedback signal (f ｎ ) generates a feedback signal (f ｎ－ｄ ) based on a comparison between the measured current (m ｎ－ｄ ) and a model-based estimated current (y ｎ ) that is time-aligned with the measured current, and When the amplitude of the predicted current (y ｅ，ｎ＋１ ), is higher than a threshold value (I ｍａｘ ), the output audio sample (u ｎ ) is either the input audio sample (r ｎ ) or the replacement audio sample (u Ｌ，ｎ ) for the current time step.

10. A computer program comprising computer-executable instructions that, when executed by at least one processor, cause a device to execute the method according to claim 9.

11. A device for use with a plant (125, 525) comprising a loudspeaker set (120, 520), the device comprising - Input audio sample (r ｎ ) and the measurement current (m ｎ－ｄ ) drawn by the loudspeaker set, and obtain them - Generate an output audio sample (u ｎ ) for the current time step, and - For the current time step, using the state space model of the loudspeaker set, from the output audio sample (u ｎ ), generate the state vector (x ｎ ) of the current drawn by the loudspeaker set and the model-based estimated current (y ｎ ); and - Based on the state vector (x ｎ ), generate a predicted current (y ｅ，ｎ＋１ ) for the next time step, and - For the current time step, a replacement audio sample (u ｎ ), based on the state vector (x Ｌ，ｎ ), where the replacement audio sample (u Ｌ，ｎ ) is such that the amplitude of the current drawn by the loudspeaker set is limited to a maximum value, generate the replacement audio sample (u Ｌ，ｎ ); – for said next time step, a feedback signal (f ｎ＋１ ), supplied to the state space model to contribute to the generation of said state vector (x ｎ ), wherein said feedback signal (f ｎ ) is a feedback signal (f ｎ－ｄ ) generated based on a comparison between said measured current (m ｎ－ｄ ) and a model-based estimated current (y ｎ ) time-aligned with said measured current, and executing a method comprising: When the amplitude of the predicted current (y ｅ，ｎ＋１ ), is higher than the threshold value (I ｍａｘ ), the output audio sample (u ｎ ) is either the input audio sample (r ｎ ) or the replacement audio sample (u Ｌ，ｎ ) for the current time step, the device.

12. The signal processing means comprises at least one processor and at least one memory comprising computer program instructions, the at least one memory and the computer program instructions being configured to cause the at least one processor to cause the device to execute at least one step of the method, the device according to claim 11.

13. The device according to claim 11 or 12, wherein the signal processing means comprises a circuit configured to cause the device to execute at least one step of the method.

14. The device according to any one of claims 10 to 13, wherein the signal processing means comprises a digital signal processor configured to cause the device to execute at least one step of the method.

15. A system (190) comprising a device (100) according to any one of claims 1 to 8 or 11 to 14, the system comprising a database configured to store model coefficients of a state space model for a plurality of loudspeaker sets, and means for loading the model coefficients corresponding to the loudspeaker set, the system (190).

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