JP2018019168A - Audio device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform control in consideration of a change of a signal waveform due to an analog circuit with an inexpensive constitution concerning an audio device including the analog circuit between a digital signal processing device and a sound output device.SOLUTION: An audio device 100 includes: an output circuit 8 for receiving an input of a second digital signal SD2 and outputting an analog output signal SAO containing a sound component to a sound output device 9; a simulation filter part 10 for receiving an input of a second digital signal SD2 and outputting a third digital signal SD3 corresponding to an analog output signal SAO; and a control section 14 for controlling an operation of an amplifier 7 included in the output circuit 8 or an operation of a sound signal processing section 3 with the use of a third digital signal SD3. The output circuit 8 is constituted by an analog circuit 23 and also the simulation filter part 10 is constituted by a digital filter corresponding to the analog circuit 23.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an audio apparatus.

  Conventionally, in an audio device, an analog circuit is provided between a digital signal processing device such as a DSP (Digital Signal Processor) and an audio output device such as a speaker. The analog circuit includes, for example, an amplifier configured by an analog IC (Integrated Circuit). In an in-vehicle audio apparatus, an AB class amplifier using a BTL (Bridged Transless) system is used. The analog circuit includes a capacitor for capacitive coupling connected to the input terminal of the amplifier, a so-called “coupling capacitor”.

  The output signal of the analog circuit usually includes a component (hereinafter referred to as “audio component”) corresponding to the audio to be reproduced. In addition, the output signal of the analog circuit may include a DC component in addition to the audio component due to degradation of the coupling capacitor or the amplifier.

  The output signal of the analog circuit is input to the speaker. When a DC component is included in the input signal of the speaker, a so-called “DC offset” occurs, and the speaker is damaged by the DC component. In view of this, a technique has been developed for protecting a speaker from a direct current component by detecting the occurrence of a direct current offset and stopping the operation of the amplifier when the direct current offset occurs.

  For example, some class AB amplifiers have terminals for detecting DC offset. This amplifier compares the voltage value of the output signal with a predetermined threshold value (for example, 2 volts). If the voltage value exceeds the threshold value, the amplifier detects a predetermined signal (hereinafter referred to as “DC offset detection signal”) from the DC offset detection terminal. Is output. A control device such as a microcontroller (hereinafter referred to as “microcomputer”) detects the occurrence of a DC offset using a DC offset detection signal.

  Here, when the amplitude of the audio component is large, the voltage value of the output signal may temporarily exceed the threshold value in a state where the output signal of the amplifier does not include a DC component. In this case, the amplifier outputs a DC offset detection signal even though no DC offset has occurred. As a result, there is a problem that erroneous detection of the DC offset occurs.

  In order to solve this problem, a technique for avoiding erroneous detection of a DC offset has been developed. For example, the acoustic device disclosed in Patent Document 1 includes a level detection unit 19, a coupling capacitor C 1, and a power AMP 15 between the signal processing unit 14 and the speaker 16. The level detector 19 detects the voltage level of the analog signal output from the signal processor 14. Further, the acoustic device of Patent Document 1 includes an LPF 17 between the power AMP 15 and the microcomputer 12. The LPF 17 smoothes the offset detection signal output from the power AMP 15. The microcomputer 12 compares the voltage value of the smoothed offset detection signal with a threshold set for each voltage level of the analog signal. When the voltage value is equal to or greater than the threshold value, the microcomputer 12 outputs a standby processing signal for setting the power AMP 15 in the standby state (see the summary of Patent Document 1, FIG. 2 and the like).

  That is, the acoustic device of Patent Document 1 performs control for avoiding erroneous detection of a DC offset by feedback of an output analog signal. Such analog signal feedback is used for various controls in audio devices as well as control for avoiding erroneous detection of DC offset.

JP 2004-320273 A

  The acoustic device of Patent Document 1 is provided with a dedicated circuit (level detection unit 19) for detecting the voltage level of an analog signal. For this reason, there was a problem that the cost increased. Further, the acoustic device of Patent Document 1 detects the voltage level of the analog signal output from the signal processing unit 14. For this reason, in the control for avoiding erroneous detection of the DC offset, there has been a problem that it is not possible to consider the change in the signal waveform due to the analog circuit downstream of the signal processing unit 14, that is, the coupling capacitor C1 and the power AMP15.

  As described above, the problem that the cost increases due to the circuit for feeding back the analog signal and the problem that the change of the signal waveform due to the analog circuit cannot be taken into account are caused by the control for avoiding the erroneous detection of the DC offset. Of course, this was a problem that occurred in general control by feedback of analog signals.

  The present invention has been made in order to solve the above-described problems. In an audio apparatus in which an analog circuit is provided between a digital signal processing apparatus and an audio output apparatus, the signal from the analog circuit can be obtained at a low cost. The purpose is to execute control in consideration of the change of the waveform.

  An audio apparatus according to the present invention receives an input of a first digital signal indicating audio information and outputs a second digital signal obtained by performing audio signal processing on the first digital signal, and a second digital signal And an output circuit for outputting an analog output signal including a sound component to the sound output device, and a simulation filter for receiving a second digital signal and outputting a third digital signal corresponding to the analog output signal And a control unit that controls the operation of the amplifier included in the output circuit or the operation of the audio signal processing unit using the third digital signal, the output circuit is configured by an analog circuit, and The simulated filter unit is constituted by a digital filter corresponding to an analog circuit.

  The audio device of the present invention has a digital filter corresponding to an analog circuit, and uses the output signal of this digital filter for control instead of feedback of the analog signal. For this reason, the control which considered the change of the signal waveform by an analog circuit can be performed with the cheap structure which does not require the circuit for feedback.

FIG. 2 is a functional block diagram showing a main part of the audio device according to Embodiment 1 of the present invention. It is a hardware block diagram which shows the principal part of the audio apparatus which concerns on Embodiment 1 of this invention. 4 is a flowchart showing an operation of the audio apparatus according to Embodiment 1 of the present invention. It is a circuit diagram showing an example of an analog circuit formed by connecting a coupling capacitor between a DA converter and an amplifier. FIG. 5A is a characteristic diagram showing an output signal of the DA converter in FIG. FIG. 5B is a characteristic diagram showing an input signal of the amplifier in FIG. It is a functional block diagram which shows the principal part of the audio apparatus which concerns on Embodiment 2 of this invention. 7 is a flowchart showing an operation of the audio apparatus according to the second embodiment of the present invention. It is a functional block diagram which shows the principal part of the audio apparatus which concerns on Embodiment 3 of this invention. It is a flowchart which shows the operation | movement of the audio apparatus based on Embodiment 3 of this invention.

Embodiment 1 FIG.
FIG. 1 is a functional block diagram showing the main part of the audio apparatus according to Embodiment 1 of the present invention. FIG. 2 is a hardware configuration diagram showing the main part of the audio apparatus according to Embodiment 1 of the present invention. With reference to FIG.1 and FIG.2, the audio apparatus 100 of Embodiment 1 is demonstrated centering on the example mounted in the vehicle 1 which consists of a four-wheeled vehicle.

  The sound source device 2 reads audio information stored in an electronic medium (not shown), and outputs a digital signal (hereinafter referred to as “first digital signal”) SD1 indicating the audio information. The sound source device 2 includes, for example, a CD (Compact Disc) drive, a USB (Universal Serial Bus) flash drive, a memory card reader, a portable information terminal such as a smartphone, or a portable music player.

  The audio signal processing unit 3 receives an input of the first digital signal SD1. The audio signal processing unit 3 performs audio signal processing on the first digital signal SD1, and outputs a digital signal (hereinafter referred to as “second digital signal”) SD2 on which the audio signal processing has been performed. The audio signal processing by the audio signal processing unit 3 corresponds to, for example, processing for setting the gain (hereinafter simply referred to as “gain”) of the second digital signal SD2 with respect to the first digital signal SD1, and audio in each frequency band. For example, a process for setting each component level (so-called “equalizer”).

  The digital-analog converter (hereinafter referred to as “DA converter”) 4 receives an input of the second digital signal SD2. The DA converter 4 converts the second digital signal SD2 into an analog signal and outputs the analog signal. The DA converter 4 is configured by a dedicated analog IC, for example.

  The band pass filter 5 allows only components within a predetermined frequency band to pass through the analog signal output from the DA converter 4. The band pass filter 5 is configured by, for example, an RLC circuit using a resistor, an inductor, and a capacitor. Or, for example, the band pass filter 5 uses an operational amplifier.

  The coupling capacitor 6 is composed of, for example, a capacitor connected in series between the output terminal of the bandpass filter 5 and the input terminal of the amplifier 7. The coupling capacitor 6 capacitively couples the band pass filter 5 and the amplifier 7.

  The amplifier 7 is constituted by, for example, a dedicated analog IC. Specifically, for example, the amplifier 7 uses a BTL class AB amplifier. The amplifier 7 amplifies the amplitude of the analog signal input to the input terminal and outputs it from the output terminal.

  The DA converter 4, the band pass filter 5, the coupling capacitor 6 and the amplifier 7 constitute an output circuit 8. That is, the output circuit 8 is composed of an analog circuit.

  Hereinafter, an analog signal output from the output circuit 8 to the audio output device 9 is referred to as an “analog output signal”. In the example of FIG. 1, the signal output from the output terminal of the amplifier 7 is the analog output signal SAO. The analog output signal SAO includes a component corresponding to the audio to be reproduced, that is, an audio component. Further, the analog output signal SAO may include a DC component in addition to the audio component due to deterioration of the coupling capacitor 6 or the amplifier 7 or the like.

  The audio output device 9 receives an analog output signal SAO and outputs audio corresponding to the audio component included in the analog output signal SAO. The audio output device 9 is constituted by, for example, a speaker mounted on the vehicle 1.

  Here, the amplifier 7 has a DC offset detection terminal. The amplifier 7 has a function of comparing the voltage value of the analog signal output from the output terminal with a predetermined threshold value (hereinafter referred to as “first threshold value”). The first threshold is set to 2 volts, for example. The amplifier 7 has a function of outputting the DC offset detection signal SDC from the DC offset detection terminal when the voltage value of the analog signal exceeds the first threshold value.

  The simulated filter unit 10 receives an input of the second digital signal SD2 and outputs a digital signal (hereinafter referred to as “third digital signal”) SD3 corresponding to the analog output signal SAO. That is, the simulation filter unit 10 is configured by a digital filter that simulates an analog circuit of the output circuit 8. Since a method for configuring a digital filter by simulating an analog circuit is known, a description thereof will be omitted. Specifically, for example, bilinear transformation or the like can be used.

  The simulation filter unit 10 ideally simulates the entire analog circuit in the output circuit 8 and simulates an actual analog circuit in the output circuit 8. However, when designing the simulated filter unit 10, a part of the analog circuit in the output circuit 8 is often unknown or undecided. In this case, the simulation filter unit 10 may simulate only a part of the analog circuit in the output circuit 8. Alternatively, the simulated filter unit 10 may simulate an unknown or undetermined portion of the analog circuit in the output circuit 8 using an equivalent circuit.

  The first amplitude value estimation unit 11 estimates the amplitude value of the audio component included in the analog output signal SAO using the third digital signal SD3. The audio component usually has a large amplitude change with respect to time. Therefore, the first amplitude value estimation unit 11 estimates the amplitude value of the audio component by peak hold or averaging processing. The first amplitude value estimation unit 11 outputs the estimated amplitude value (hereinafter referred to as “first estimated amplitude value”) to the DC offset determination unit 12.

  The DC offset determination unit 12 uses the first estimated amplitude value output from the first amplitude value estimation unit 11 and the DC offset detection signal SDC output from the amplifier 7 to determine whether a DC offset has occurred in the analog output signal SAO. It is to determine whether or not.

  Specifically, for example, the DC offset determination unit 12 repeatedly performs a process of determining whether or not the DC offset detection signal SDC is input from the amplifier 7 at a predetermined time interval. When it is determined that the DC offset detection signal SDC is input, the DC offset determination unit 12 compares the first estimated amplitude value with a predetermined threshold (hereinafter referred to as “second threshold”). For example, the second threshold is set to a value corresponding to the first threshold. The DC offset determination unit 12 continuously determines that the DC offset detection signal SDC is input in a state where the first estimated amplitude value is equal to or less than the second threshold (hereinafter, “first input determination number”). Count). The DC offset determination unit 12 compares the first input determination number with a predetermined reference number. The DC offset determination unit 12 determines that a DC offset has occurred in the analog output signal SAO when the first input determination number is equal to or greater than the reference number.

  The DC offset protection unit 13 protects the audio output device 9 from DC components by controlling the operation of the amplifier 7 when the DC offset determination unit 12 determines that a DC offset has occurred. Specifically, for example, the DC offset protection unit 13 stops the operation of the amplifier 7 by setting the amplifier 7 to a standby state.

  The first amplitude value estimation unit 11, the DC offset determination unit 12, and the DC offset protection unit 13 constitute a control unit 14. The audio signal processing unit 3, the output circuit 8, the simulation filter unit 10, and the control unit 14 constitute a main part of the audio device 100.

  FIG. 2 shows an example of a hardware configuration of a main part of the audio device 100. The audio signal processing unit 3 and the first amplitude value estimation unit 11 shown in FIG. 1 are configured by a digital signal processing device 21 such as a DSP. The DC offset determination unit 12 and the DC offset protection unit 13 illustrated in FIG. 1 are configured by a control device 22 such as a microcomputer. The output circuit 8 shown in FIG. 1 includes an analog circuit 23. The simulated filter unit 10 shown in FIG. 1 is configured by a digital filter that simulates an analog circuit 23, and this digital filter is provided in the digital signal processing device 21.

  Next, with reference to the flowchart of FIG. 3, the operation of the audio device 100 will be described focusing on the operations of the DC offset determination unit 12 and the DC offset protection unit 13. In the initial state, the audio device 100 is reproducing sound. The first amplitude value estimating unit 11 estimates the amplitude value of the audio component included in the analog output signal SAO using the third digital signal SD3, and continues the process of outputting the first estimated amplitude value to the DC offset determining unit 12. doing.

  First, in step ST1, the DC offset determination unit 12 sets the count value of the first input determination number to 0. Next, in step ST2, the DC offset determination unit 12 sets a predetermined waiting time. When the waiting time has elapsed, in step ST <b> 3, the DC offset determination unit 12 determines whether or not the DC offset detection signal SDC is input from the amplifier 7. When the DC offset detection signal SDC is not input (step ST3 “NO”), the DC offset determination unit 12 returns to the process of step ST1.

  When the DC offset detection signal SDC is input (step ST3 “YES”), in step ST4, the DC offset determination unit 12 receives the latest first estimated amplitude value input from the first amplitude value estimation unit 11. Compare with the second threshold. When the first estimated amplitude value is larger than the second threshold value (step ST4 “NO”), the DC offset determination unit 12 returns to the process of step ST2.

  When the first estimated amplitude value is equal to or smaller than the second threshold value (step ST4 “YES”), in step ST5, the direct current offset determination unit 12 increases the count value of the first input determination number by one. Next, in step ST6, the DC offset determination unit 12 determines whether or not the first input determination number is equal to or greater than the reference number. When the first input determination number is less than the reference number (step ST6 “NO”), the DC offset determination unit 12 returns to the process of step ST2.

  When the first input determination number is equal to or greater than the reference number (step ST6 “YES”), in step ST7, the DC offset protector 13 sets the amplifier 7 to the standby state, thereby operating the amplifier 7. Stop. As a result, it is possible to prevent the audio output device 9 from being damaged by a DC component included in the analog output signal SAO. That is, the audio output device 9 can be protected from the DC component.

  As described above, the audio device 100 according to the first embodiment includes the simulation filter unit 10 corresponding to the output circuit 8. The first amplitude value estimation unit 11 uses the output signal (third digital signal SD3) of the simulation filter unit 10 instead of the feedback of the analog output signal SAO, and calculates the amplitude value of the audio component included in the analog output signal SAO. presume. This eliminates the need for a dedicated circuit (such as the level detection unit of Patent Document 1) for detecting the amplitude value of the audio component, thereby reducing the cost. Further, in determining whether or not a DC offset has occurred in the analog output signal SAO, changes in the signal waveform due to the output circuit 8 including the coupling capacitor 6 and the amplifier 7 can be taken into consideration.

  Here, with reference to FIG. 4 and FIG. 5, an example of the change of the signal waveform by an analog circuit is demonstrated. As shown in FIG. 4, a coupling capacitor 6 'is connected between the DA converter 4' and the amplifier 7 '. The amplifier 7 'uses a class AB amplifier. At this time, a high-pass filter is constituted by the capacitance of the coupling capacitor 6 'and the input impedance of the amplifier 7'. The capacitance value of the coupling capacitor 6 'is set to 0.22 microfarads (µF), and the input impedance value of the amplifier 7' is set to 100 kilohms (kΩ).

  FIG. 5A shows the waveform of the output signal of the DA converter 4 'in FIG. On the other hand, FIG. 5B shows the waveform of the input signal to the amplifier 7 'in FIG. As shown in FIG. 5, due to the electrical characteristics of the high-pass filter, the waveform of the input signal of the amplifier 7 'changes with respect to the output signal of the DA converter 4'.

  As in the acoustic device of Patent Document 1, the configuration that feeds back the analog signal in the previous stage of the coupling capacitor cannot take into account changes in the signal waveform caused by the coupling capacitor 6 ′ and the amplifier 7 ′ as shown in FIG. There was a problem. On the other hand, the audio apparatus 100 according to Embodiment 1 uses the output signal (third digital signal SD3) of the simulation filter unit 10 in determining whether or not a DC offset has occurred in the analog output signal SAO. Thus, it is possible to consider a change in signal waveform caused by the output circuit 8 including the coupling capacitor 6 and the amplifier 7. As a result, it is possible to improve the accuracy of determining whether or not a DC offset has occurred.

  Also, the audio apparatus 100 according to Embodiment 1 compares the first estimated amplitude value with the second threshold value, and the DC offset detection signal SDC is input when the first estimated amplitude value is equal to or smaller than the second threshold value. The number of times determined to be (the number of first input determinations) is counted. In other words, the audio apparatus 100 excludes the DC offset detection signal SDC when the first estimated amplitude value is larger than the second threshold value from the count target. As a result, when the amplitude of the audio component included in the analog output signal SAO is large, it is possible to suppress erroneous determination that a DC offset has occurred in a state where no DC offset has occurred in the analog output signal SAO. Can do. As a result, it is possible to further improve the accuracy of determining whether or not a DC offset has occurred. In addition, the cost can be further reduced because a filter circuit (such as LPF in Patent Document 1) for smoothing the DC offset detection signal SDC is not required while improving the determination accuracy.

  Note that the audio signal processing by the audio signal processing unit 3 is not limited to the process of setting the gain and the process of the equalizer. The audio signal processing unit 3 may perform any audio signal processing on the first digital signal SD1.

  The amplifier 7 only needs to have a terminal for detecting a DC offset, and is not limited to an AB class amplifier using the BTL method. The amplifier 7 may be, for example, a class A or class B amplifier.

  Further, the circuit configuration of the output circuit 8 is not limited to the example shown in FIG. The output circuit 8 has any circuit configuration as long as it includes an amplifier 7 and outputs an analog signal (analog output signal SAO) in response to an input of a digital signal (second digital signal SD2). May be. For example, the output circuit 8 may be obtained by removing the band pass filter 5 shown in FIG. The output circuit 8 may be a circuit in which another band pass filter or the like is added to the subsequent stage of the amplifier 7.

  The audio device 100 is not limited to being mounted on a vehicle, and may be any audio device. The audio device 100 may be, for example, a home audio device or a business audio device.

  Further, the determination method by the DC offset determination unit 12 is not limited to the method described with reference to FIG. In the second embodiment to be described later, another determination method will be described.

  The control by the control unit 14 is limited to the control for determining whether or not a DC offset is generated in the analog output signal SAO and stopping the operation of the amplifier 7 when the DC offset is generated. is not. The control unit 14 may perform any control as long as it controls the operation of the amplifier 7 or the operation of the audio signal processing unit 3 using the third digital signal SD3. In the third embodiment to be described later, another control will be described.

  As described above, the audio apparatus 100 according to Embodiment 1 receives the input of the first digital signal SD1 indicating the audio information, and outputs the second digital signal SD2 obtained by performing the audio signal processing on the first digital signal SD1. Receiving the input of the second digital signal SD2 and the output circuit 8 for outputting the analog output signal SAO including the sound component to the sound output device 9, and receiving the input of the second digital signal SD2. Thus, the operation of the amplifier 7 included in the output circuit 8 or the sound signal processing unit 3 using the simulation filter unit 10 that outputs the third digital signal SD3 corresponding to the analog output signal SAO and the third digital signal SD3. The output circuit 8 is constituted by an analog circuit 23, and the simulation filter unit 10 is an analog circuit 23. It is constituted by a digital filter corresponding to the grayed circuit 23. By using the output signal (third digital signal SD3) of the digital filter instead of the feedback of the analog output signal SAO, a dedicated circuit for feeding back the analog output signal SAO is unnecessary, and the cost can be reduced. . Further, in the control of the control unit 14, changes in the signal waveform due to the analog circuit 23 including the amplifier 7 can be considered.

  The output circuit 8 includes a coupling capacitor 6 connected to the input terminal of the amplifier 7. Thereby, in the control of the control unit 14, it is possible to consider a change in signal waveform due to the output circuit 8 including the coupling capacitor 6 and the amplifier 7.

  The audio signal processing unit 3 includes a digital signal processing device 21, and a digital filter is provided in the digital signal processing device 21. By using the digital filter in the digital signal processing device 21 for the simulated filter unit 10, the number of parts of the audio device 100 can be reduced, and the audio device 100 can be downsized.

  The amplifier 7 includes an output terminal and a DC offset detection terminal. When the voltage value of the analog signal output from the output terminal exceeds the first threshold value, the DC offset detection signal is output from the DC offset detection terminal. The controller 14 has a function of outputting SDC, and the control unit 14 uses the third digital signal SD3 to estimate the amplitude value (first estimated amplitude value) of the speech component, and the first estimation. A DC offset determination unit 12 that determines whether or not a DC offset has occurred in the analog output signal SAO using the amplitude value and the DC offset detection signal SDC, and an amplifier that determines that a DC offset has occurred And a DC offset protection unit 13 that stops the operation of No. 7. Thereby, it is determined whether or not a DC offset is generated in the analog output signal SAO, and in the control for stopping the operation of the amplifier 7 when the DC offset is generated, the signal waveform change by the output circuit 8 is changed. Can be considered. As a result, it is possible to improve the accuracy of determining whether or not a DC offset has occurred. In addition, a filter circuit for smoothing the DC offset detection signal SDC is not required while improving the determination accuracy, and the cost can be further reduced.

  In addition, the DC offset determination unit 12 repeatedly executes a process of determining whether or not the DC offset detection signal SDC is input, and the DC offset detection signal SDC when the first estimated amplitude value is equal to or smaller than the second threshold value. Is counted as the first input determination number, and if the first input determination number is equal to or greater than the reference number, it is determined that a DC offset has occurred. By excluding the DC offset detection signal SDC when the first estimated amplitude value is larger than the second threshold from the count target, when the audio component has a large amplitude value, a DC offset is not generated. Thus, erroneous determination that a DC offset has occurred can be suppressed. As a result, it is possible to further improve the accuracy of determining whether or not a DC offset has occurred.

  The audio device 100 is for vehicle use. The audio device 100 can be used for any audio device, and can also be used for an on-vehicle audio device.

Embodiment 2. FIG.
FIG. 6 is a functional block diagram showing the main part of the audio apparatus according to Embodiment 2 of the present invention. With reference to FIG. 6, the audio apparatus 100a of Embodiment 2 is demonstrated. In FIG. 6, the same blocks as those in the functional block diagram of the first embodiment shown in FIG.

  The DC offset determination unit 12a uses the first estimated amplitude value output from the first amplitude value estimation unit 11 and the DC offset detection signal SDC output from the amplifier 7 to generate a DC offset in the analog output signal SAO. It is to determine whether or not.

  Specifically, for example, the DC offset determination unit 12a repeatedly performs a process of determining whether or not the DC offset detection signal SDC is input from the amplifier 7 at a predetermined time interval. The DC offset determination unit 12a counts the number of times that the DC offset detection signal SDC is continuously input (hereinafter referred to as “second input determination number”). The DC offset determination unit 12a sets the reference number to be compared with the second input determination number to a number corresponding to the first estimated amplitude value. For example, the reference number is set to a larger number as the first estimated amplitude value is larger, and is set to a smaller number as the first estimated amplitude value is smaller. The DC offset determination unit 12a compares the second input determination number with the reference number, and determines that a DC offset has occurred in the analog output signal SAO when the second input determination number is equal to or greater than the reference number. To do.

  The DC offset protection unit 13 protects the audio output device 9 from the DC component by controlling the operation of the amplifier 7 when the DC offset determination unit 12a determines that a DC offset has occurred. Specifically, for example, the DC offset protection unit 13 stops the operation of the amplifier 7 by setting the amplifier 7 to a standby state.

  The first amplitude value estimating unit 11, the DC offset determining unit 12a, and the DC offset protecting unit 13 constitute a control unit 14a. The audio signal processing unit 3, the output circuit 8, the simulation filter unit 10, and the control unit 14a constitute a main part of the audio device 100a.

  The hardware configuration of the audio device 100a is the same as the hardware configuration of the audio device 100 shown in FIG. 2, and thus will be described with reference to FIG. That is, the audio signal processing unit 3 and the first amplitude value estimation unit 11 shown in FIG. 6 are configured by a digital signal processing device 21 such as a DSP. The DC offset determination unit 12a and the DC offset protection unit 13 illustrated in FIG. 6 are configured by a control device 22 such as a microcomputer. The output circuit 8 shown in FIG. 6 includes an analog circuit 23. The simulated filter unit 10 shown in FIG. 6 is configured by a digital filter that simulates the analog circuit 23, and this digital filter is provided in the digital signal processing device 21.

  Next, the operation of the audio device 100a will be described with reference to the flowchart of FIG. 7, focusing on the operations of the DC offset determination unit 12a and the DC offset protection unit 13. In an initial state, the audio device 100a is reproducing audio. The first amplitude value estimation unit 11 estimates the amplitude value of the audio component included in the analog output signal SAO using the third digital signal SD3, and continues the process of outputting the first estimated amplitude value to the DC offset determination unit 12a. doing.

  First, in step ST11, the DC offset determination unit 12a sets the count value of the second input determination count to zero. Next, in step ST12, the DC offset determination unit 12a uses the latest first estimated amplitude value input from the first amplitude value estimation unit 11, and sets a reference count according to the first estimated amplitude value. .

  Next, in step ST13, the DC offset determination unit 12a sets a predetermined waiting time. When the waiting time has elapsed, in step ST14, the DC offset determination unit 12a determines whether or not the DC offset detection signal SDC is input from the amplifier 7. When the DC offset detection signal SDC is not input (step ST14 “NO”), the DC offset determination unit 12a returns to the process of step ST11.

  When the DC offset detection signal SDC is input (step ST14 “YES”), in step ST15, the DC offset determination unit 12a increases the count value of the second input determination count by one. Next, in step ST16, the DC offset determination unit 12a compares the second input determination number with the reference number set in step ST12. When the second input determination number is less than the reference number (step ST16 “NO”), the DC offset determination unit 12a returns to the process of step ST13.

  When the second input determination number is equal to or greater than the reference number (step ST16 “YES”), in step ST17, the DC offset protection unit 13 sets the amplifier 7 to the standby state, thereby operating the amplifier 7. Stop. As a result, it is possible to prevent the audio output device 9 from being damaged by a DC component included in the analog output signal SAO. That is, the audio output device 9 can be protected from the DC component.

  Similarly to the audio device 100 of the first embodiment, the audio device 100a of the second embodiment does not require a dedicated circuit (such as the level detection unit of Patent Document 1) for detecting the amplitude value of the audio component. For this reason, cost can be reduced.

  Similarly to the audio device 100 of the first embodiment, the audio device 100a of the second embodiment includes the coupling capacitor 6 and the amplifier 7 in determining whether or not a DC offset has occurred in the analog output signal SAO. Changes in the signal waveform due to the included output circuit 8 can be taken into account. As a result, it is possible to improve the accuracy of determining whether or not a DC offset has occurred.

  In addition, the audio device 100a according to the second embodiment sets the reference number corresponding to the first estimated amplitude value, and the number of times that the DC offset detection signal SDC is determined to be input (second input determination number) is the reference. If the number is equal to or greater than the number of times, it is determined that a DC offset has occurred. As a result, when the amplitude of the audio component included in the analog output signal SAO is large, it is possible to suppress erroneous determination that a DC offset has occurred in a state where no DC offset has occurred in the analog output signal SAO. Can do. As a result, it is possible to further improve the accuracy of determining whether or not a DC offset has occurred. In addition, the cost can be further reduced because a filter circuit (such as LPF in Patent Document 1) for smoothing the DC offset detection signal SDC is not required while improving the determination accuracy.

  Note that the audio device 100a according to the second embodiment can employ various modifications similar to those described in the first embodiment.

  As described above, the DC offset determination unit 12a according to the second embodiment repeatedly executes the process of determining whether or not the DC offset detection signal SDC is input, and the DC offset detection signal SDC is input. When the number of times of continuous determination (second input determination number) is counted and the second input determination number is equal to or greater than the reference number set according to the first estimated amplitude value, it is determined that a DC offset has occurred. To do. As a result, when the amplitude of the audio component included in the analog output signal SAO is large, it is possible to suppress erroneous determination that a DC offset has occurred in a state where no DC offset has occurred in the analog output signal SAO. Can do. As a result, it is possible to improve the accuracy of determining whether or not a DC offset has occurred.

Embodiment 3 FIG.
FIG. 8 is a functional block diagram showing the main part of the audio apparatus according to Embodiment 3 of the present invention. With reference to FIG. 8, the audio apparatus 100b of Embodiment 3 is demonstrated. In FIG. 8, blocks similar to those in the functional block diagram of the first embodiment shown in FIG.

  The second amplitude value estimation unit 11b estimates the amplitude value of the analog output signal SAO using the third digital signal SD3. Since the analog output signal SAO includes an audio component, the amplitude change with respect to time is usually large. Therefore, the second amplitude value estimation unit 11b estimates the amplitude value of the analog output signal SAO by peak hold or averaging processing. The second amplitude value estimation unit 11b outputs the estimated amplitude value (hereinafter referred to as “second estimated amplitude value”) to the clip determination unit 12b.

  In general, distortion of a signal waveform caused by limiting the amplitude value of an analog signal to a value equal to or less than a predetermined value is referred to as “clip”. The clip determination unit 12b determines whether or not a clip has occurred in the analog output signal SAO using the second estimated amplitude value output from the second amplitude value estimation unit 11b.

  Specifically, for example, the clip determination unit 12b compares the second estimated amplitude value with a predetermined threshold value (hereinafter referred to as “third threshold value”). The third threshold value is set to a value corresponding to the maximum amplitude value that can be output from the output terminal of the amplifier 7, for example. When the second estimated amplitude value is larger than the third threshold value, the clip determination unit 12b determines that a clip has occurred in the analog output signal SAO.

  The clip suppression unit 13b is configured to suppress clipping in the analog output signal SAO by controlling the operation of the audio signal processing unit 3 when the clip determination unit 12b determines that a clip has occurred. Specifically, for example, the clip suppression unit 13b reduces the gain of the audio signal processing unit 3 with respect to the normal gain.

  That is, the clip suppression unit 13b sets a value of a reduction amount with respect to the gain of the audio signal processing unit 3 (hereinafter referred to as “gain reduction value”). The gain reduction value is a value of 0 dB or less, and is set to a value of 1 dB interval, for example. The clip suppression unit 13 b outputs the set gain reduction value to the audio signal processing unit 3. When the gain reduction value is input from the clip suppression unit 13b, the audio signal processing unit 3 reduces the gain according to the gain reduction value.

  When a clip is generated in the analog output signal SAO, the sound quality of the sound output from the sound output device 9 is degraded. When the clip suppression unit 13b suppresses the clip, it is possible to suppress a decrease in sound quality.

  The second amplitude value estimation unit 11b, the clip determination unit 12b, and the clip suppression unit 13b constitute a control unit 14b. The audio signal processing unit 3, the output circuit 8, the simulation filter unit 10, and the control unit 14b constitute a main part of the audio device 100b.

  The hardware configuration of the audio device 100b is the same as the hardware configuration of the audio device 100 shown in FIG. 2, and will be described with reference to FIG. That is, the audio signal processing unit 3 and the second amplitude value estimation unit 11b illustrated in FIG. 8 are configured by a digital signal processing device 21 such as a DSP. The clip determination unit 12b and the clip suppression unit 13b illustrated in FIG. 8 are configured by a control device 22 such as a microcomputer. The output circuit 8 shown in FIG. 8 includes an analog circuit 23. The simulated filter unit 10 shown in FIG. 8 is configured by a digital filter that simulates the analog circuit 23, and this digital filter is provided in the digital signal processing device 21.

  Next, the operation of the audio device 100b will be described with reference to the flowchart of FIG. 9, focusing on the operations of the clip determination unit 12b and the clip suppression unit 13b. In the initial state, the audio device 100b is reproducing sound. The second amplitude value estimation unit 11b continues the process of estimating the amplitude value of the analog output signal SAO using the third digital signal SD3 and outputting the second estimated amplitude value to the clip determination unit 12b.

  First, in step ST21, the clip suppression unit 13b sets the gain decrease value to 0 dB. Next, in step ST22, the clip determination unit 12b compares the latest second estimated amplitude value input from the second amplitude value estimation unit 11b with the third threshold value.

  Next, in step ST23, the clip determination unit 12b determines whether a clip is generated in the analog output signal SAO using the comparison result in step ST22. That is, when the second estimated amplitude value is larger than the third threshold value, the clip determination unit 12b determines that a clip has occurred in the analog output signal SAO. On the other hand, if the second estimated amplitude value is equal to or smaller than the third threshold value, the clip determination unit 12b determines that no clip has occurred in the analog output signal SAO.

  When it is determined that a clip has occurred (step ST23 “YES”), in step ST24, the clip suppression unit 13b sets the gain decrease value to a value lower by 1 decibel. For example, if the gain reduction value is set to 0 dB immediately before step ST24, the clip suppression unit 13b sets the gain reduction value to -1 dB in step ST24. The clip suppression unit 13 b outputs the newly set gain reduction value to the audio signal processing unit 3. Next, the process of the control unit 14b returns to step ST22.

  When it is determined that no clip has occurred (step ST23 “NO”), in step ST25, the clip suppression unit 13b determines whether or not the gain decrease value is set to a value of −1 decibel or less. . When the gain decrease value is set to a value higher than -1 decibel, that is, 0 decibel (step ST25 "NO"), the process of the control unit 14b returns to step ST22.

  When the gain decrease value is set to a value equal to or less than −1 decibel (step ST25 “YES”), in step ST26, the clip suppression unit 13b sets the gain decrease value to a value higher by 1 decibel. For example, if the gain decrease value is set to -3 dB immediately before step ST26, the clip suppression unit 13b sets the gain decrease value to -2 decibels in step ST26. The clip suppression unit 13 b outputs the newly set gain reduction value to the audio signal processing unit 3. Next, the process of the control unit 14b returns to step ST22.

  As described above, the audio device 100b according to the third embodiment uses the output signal (third digital signal SD3) of the simulation filter unit 10 configured by a digital filter to output the output signal (analog output signal SAO) of the output circuit 8. ) To determine whether a clip has occurred. Therefore, when the amplifier 7 does not have a clip detection terminal (for example, when the amplifier 7 is configured by a class D amplifier, or when the amplifier 7 is configured by a class AB amplifier with a small number of terminals). ), It can be determined whether or not a clip has occurred. Further, a dedicated circuit for detecting the amplitude value of the analog output signal SAO is not necessary, and the cost can be reduced.

  In addition, the audio device 100b according to the third embodiment uses the third digital signal SD3 to determine whether or not a clip has occurred, so that the signal waveform generated by the output circuit 8 including the coupling capacitor 6 and the amplifier 7 is used. Can be considered. As a result, it is possible to improve the accuracy of determining whether or not a clip has occurred.

  The amplifier 7 in the third embodiment may not have a DC offset detection terminal, or may use a class D amplifier. When a class D amplifier is used as the amplifier 7, the output circuit 8 may be a circuit in which a digital / analog conversion filter circuit is added after the amplifier 7.

  In addition, the audio device 100b according to the third embodiment can employ various modifications similar to those described in the first embodiment.

  As described above, the control unit 14b according to the third embodiment uses the third digital signal SD3 to estimate the amplitude value (second estimated amplitude value) of the analog output signal SAO, and the second amplitude value estimating unit 11b. (2) A clip determination unit 12b that determines whether or not a clip has occurred in the analog output signal SAO using the estimated amplitude value; and if it is determined that a clip has occurred, the gain of the audio signal processing unit 3 is reduced The clip suppression part 13b to be made is provided. As a result, even when the amplifier 7 does not have a clip detection terminal, it can be determined whether or not clipping has occurred in the analog output signal SAO.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  DESCRIPTION OF SYMBOLS 1 Vehicle, 2 Sound source device, 3 Audio | voice signal processing part, 4 DA converter, 5 Band pass filter, 6 Coupling capacitor, 7 Amplifier, 8 Output circuit, 9 Voice output device, 10 Simulation filter part, 11 1st amplitude Value estimation unit, 11b second amplitude value estimation unit, 12, 12a DC offset determination unit, 12b clip determination unit, 13 DC offset protection unit, 13b clip suppression unit, 14, 14a, 14b control unit, 21 digital signal processing device, 22 control device, 23 analog circuit, 100, 100a, 100b audio device.

Claims (9)

An audio signal processing unit that receives an input of a first digital signal indicating audio information and outputs a second digital signal obtained by performing audio signal processing on the first digital signal;
An output circuit for receiving an input of the second digital signal and outputting an analog output signal including an audio component to an audio output device;
A simulation filter unit that receives an input of the second digital signal and outputs a third digital signal corresponding to the analog output signal;
A control unit that controls the operation of the amplifier included in the output circuit or the operation of the audio signal processing unit using the third digital signal;
The audio device, wherein the output circuit is configured by an analog circuit, and the simulated filter unit is configured by a digital filter corresponding to the analog circuit.   2. The audio apparatus according to claim 1, wherein the output circuit includes a coupling capacitor connected to an input terminal of the amplifier.   3. The audio apparatus according to claim 1, wherein the audio signal processing unit is configured by a digital signal processing apparatus, and the digital filter is provided in the digital signal processing apparatus. The amplifier includes an output terminal and a DC offset detection terminal. When the voltage value of the analog signal output from the output terminal exceeds a first threshold, the DC offset detection signal is output from the DC offset detection terminal. Has a function to output
The controller is
A first amplitude value estimator that estimates an amplitude value of the audio component using the third digital signal;
A DC offset determination unit that determines whether or not a DC offset has occurred in the analog output signal using the amplitude value and the DC offset detection signal;
If it is determined that the DC offset has occurred, a DC offset protector that stops the operation of the amplifier;
The audio apparatus according to any one of claims 1 to 3, further comprising:   The DC offset determination unit repeatedly executes a process of determining whether or not the DC offset detection signal is input, and the DC offset detection signal is input in a state where the amplitude value is equal to or less than a second threshold value. 5. The audio apparatus according to claim 4, wherein the number of times determined to be continuous is counted, and if the number is equal to or greater than a reference number, it is determined that the DC offset has occurred.   The DC offset determination unit repeatedly performs a process of determining whether or not the DC offset detection signal is input, and counts the number of times that the DC offset detection signal is continuously determined to be input, 5. The audio device according to claim 4, wherein when the number of times is equal to or greater than a reference number set in accordance with the amplitude value, it is determined that the DC offset has occurred. The controller is
A second amplitude value estimator that estimates an amplitude value of the analog output signal using the third digital signal;
A clip determination unit that determines whether or not a clip is generated in the analog output signal using the amplitude value;
If it is determined that the clip has occurred, a clip suppression unit that reduces the gain of the audio signal processing unit;
The audio apparatus according to any one of claims 1 to 3, further comprising:   8. The audio device according to claim 7, wherein the clip determination unit determines that the clip is generated when the amplitude value is larger than a third threshold value.   The audio device according to any one of claims 1 to 8, wherein the audio device is for vehicle use.

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