JP2016054438A - Audio device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery driving audio device, which can adjust clip level of sound pressure level by digital signal in response to decrease in battery voltages accompanying decrease in remaining amounts of a battery and increase in load currents.SOLUTION: In an audio device 1 driven by a battery 10, a CPU 30 executes a setting for reducing clip level, at which sound pressure level is clipped, on a DSP 40 responding to decrease in battery voltages VB outputted from the battery 10. The DSP 40 performs adjustment of click level directed from the CPU 30 to an input audio signal AIN, by digital signal processing. This can suppress load currents at a maximum sound pressure level at which the sound level is clipped so that decrease in battery voltages at the maximum sound pressure level can be prevented.SELECTED DRAWING: Figure 1

Description

  The technology disclosed in the present invention relates to an audio device, and more particularly to an audio device that is driven by power supply by a battery.

  In a battery-driven audio amplifier, it is necessary to take into consideration that the output battery voltage fluctuates with fluctuations in the remaining battery level (the amount of electrical energy stored in the battery). This is because the electric energy of the battery is consumed according to the use of the audio amplifier, the remaining battery level is reduced, and the battery voltage is lowered. Further, it is known that the battery has a finite output resistance, and a voltage drop of the battery voltage occurs according to the current taken out from the battery. In an audio amplifier, when sound output is performed in an output region with a large sound pressure level, the load current flowing through the speaker increases. In this case, it is known that when the load current is supplied from the battery, the voltage drop at the output resistance increases, and the battery voltage decreases.

  FIG. 3 is a circuit block diagram showing a general circuit configuration of the battery-powered audio amplifier 1000. For example, the battery voltage of the battery 10 in which the use battery voltage range of 3.0V to 4.2V is set is boosted by the booster circuit 20 to supply the power supply voltage to the amplifier 50 (for example, 8V). In this case, the voltage boosted by the booster circuit 20 is controlled by the voltage control circuit 100, and the voltage value is limited according to the battery voltage. For example, it is limited to a range of 5V to 8V according to a decrease in battery voltage.

  On the other hand, the audio signal input from the input terminal IN is amplified by the amplifier 50 via the DSP 40 controlled by the CPU 30 and drives the speaker 60.

  In the audio amplifier 1000, the voltage control circuit 100 reduces and limits the power supply voltage of the amplifier 50, so that the sound pressure level is clipped and output from the amplifier 50 as a circuit operation. By limiting the maximum sound pressure level to the clipped level, the load current flowing through the speaker 60 is limited. By limiting the load current, it is possible to prevent the battery voltage from falling below the operating battery voltage range.

  Note that Patent Document 1 and the like are disclosed as related prior art documents.

JP 2006-31382 A

  However, in the audio amplifier 1000 described in the above background art, the voltage control circuit 100 must be added in order to limit the power supply voltage of the amplifier 50 according to the battery voltage, which complicates the circuit configuration and increases the current consumption. Is unfavorable. Further, in the method of limiting the power supply voltage of the amplifier 50 by the voltage control circuit 100 and clipping the sound pressure level output from the amplifier 50, it is necessary to make the voltage value of the power supply voltage variable. However, it is difficult to finely control the load current by making the power supply voltage of the amplifier 50 variable, and there may be a case where it is necessary to perform control with a sufficient remaining battery capacity. The battery power is used up effectively in the battery-powered audio amplifier 1000, for example, the power supply voltage limit reaches the lower limit before the remaining battery power is used up, and the operation of the audio amplifier 1000 must be stopped. It is a problem that may not be possible.

  Some amplifiers 50 have a high operable power supply voltage range. In this case, the voltage range that can be limited by the voltage control circuit 100 is limited to a high voltage range. Since the clipable level is limited, there is a problem that it is not possible to sufficiently control the load current according to the battery voltage.

  The present application has been proposed in view of the above-described problems. In a battery-powered audio device, the sound pressure level is reduced by digital signal processing in accordance with a decrease in battery voltage accompanying a decrease in remaining battery power or an increase in load current. An object of the present invention is to provide an audio device capable of adjusting a clip level.

  The audio device according to the present application relates to an audio device driven by a battery. A DSP and a control unit are provided. The DSP performs digital signal processing on the input audio signal. A control part performs the setting which reduces the clip level which clips a sound pressure level with respect to DSP according to the fall of the battery voltage output from a battery.

  The control unit sets a clip level at which the sound pressure level is clipped according to a change in battery voltage due to a change in remaining battery level or a change in load current to be supplied from the battery. The DSP adjusts the clip level set by the control unit based on digital signal processing.

  As a result, the maximum sound pressure level is reduced by reducing the clip level for clipping the sound pressure level in response to detecting a decrease in the battery voltage due to a decrease in the remaining battery level or a decrease in the battery voltage due to an increase in the load current. The load current at this time can be reduced. In a general technique, when an audio signal having a wide sound pressure level such as classical music is reproduced, in an output region where the sound pressure level is small, the load current is not increased and the battery can be driven with a sufficient battery voltage. On the other hand, in the output region where the sound pressure level is large, the load current may increase and the battery voltage may decrease. In this case, if the battery voltage falls below a predetermined voltage, the audio device is shut down and the operation stops without using up the electric energy remaining in the battery. In the present invention, the clip level for clipping the sound pressure level is reduced in response to detecting a decrease in battery voltage. Thereby, the load current can be suppressed at the maximum sound pressure level where the sound pressure level is clipped. A decrease in battery voltage at the maximum sound pressure level is prevented. It is possible to prevent an unexpected shutdown of the audio device when the electric energy remaining in the battery is not used up. The continuous operation time of the audio device can be extended.

  The clip level of the sound pressure level can be adjusted by DSP digital signal processing. Here, the DSP is a configuration essential for normal adjustment operations of the audio apparatus such as volume adjustment, equalization adjustment, and mixing adjustment. By adjusting the clip level using the DSP which is an essential configuration, it is not necessary to add a dedicated circuit configuration for adjusting the clip level. The clip level of the sound pressure level can be adjusted without complicating the circuit configuration by adding a dedicated circuit and increasing the current consumption.

  Further, the adjustment of the clip level is an adjustment by digital signal processing by the DSP, and the adjustment range is not restricted by the control restrictions caused by the additional circuit configuration. Fine adjustment is possible by DSP digital signal processing.

  Furthermore, in the audio apparatus according to the present application, the control unit includes first comparison means for comparing the battery voltage with the first reference voltage, and whenever the first comparison means detects that the battery voltage is lower than the first reference voltage. In addition, the clip level is set to a level obtained by subtracting a predetermined level from the preset level. The first comparison means can detect a decrease in battery voltage. Although the first reference voltage is within the range of the used battery voltage range as the voltage value of the battery voltage, it is set to a voltage value that may fall below the lower limit value of the used battery voltage range due to a voltage drop depending on the load current. To do. Even when the battery voltage decreases as the remaining battery level decreases, the clip level is decreased every time it is detected that the battery voltage falls below the first reference voltage. The sound pressure level can be decreased sequentially, and the load current can be limited sequentially to prevent a decrease in battery voltage at the maximum sound pressure level.

  The control unit further includes a second comparison unit that compares the battery voltage with a second reference voltage that is higher than the first reference voltage, and detects that the battery voltage exceeds the second reference voltage by the second comparison unit. In response to this, the clip level is returned to a level obtained by adding back a predetermined level that has been reduced immediately before. Since the load current is reduced by reducing the clip level, the voltage value of the battery voltage is recovered. When the battery voltage recovers until it exceeds the first reference voltage and exceeds the second reference voltage, which is a higher voltage, the clip level can be returned to the previous clip level. Along with the recovery of the battery voltage, the clip level can be returned to a higher level, and the range of the sound pressure level that is not clipped can be expanded to perform reproduction with a more natural sound quality.

  The control unit further includes a third comparison unit that compares the battery voltage with a third reference voltage that is lower than the first reference voltage, and the third comparison unit detects that the battery voltage is lower than the third reference voltage. Command to stop the operation. As a result, if the battery voltage falls below the third reference voltage, which is lower than the first reference voltage, even if the clip level is reduced, it is determined that the battery voltage necessary for driving the audio device cannot be secured. Stop the operation. Here, the third reference voltage is, for example, the lower limit voltage value of the battery voltage range in use.

  According to the audio device according to the present application, in the battery-powered audio device, the clip level of the sound pressure level output by the digital signal processing is reduced according to the decrease in the battery voltage accompanying the decrease in the remaining battery level or the increase in the load current. Can be adjusted.

It is a circuit block diagram of audio device 1 of an embodiment. It is a flowchart at the time of adjusting a clip level. It is a circuit block diagram of the audio apparatus of a prior art.

  FIG. 1 is a circuit block diagram of an audio apparatus 1 according to an embodiment of the present application. The audio device 1 is a battery-driven device that operates using the battery 10 as a drive source.

  The battery voltage VB output from the battery 10 decreases according to the remaining battery level. A battery voltage range that can be used as the battery voltage VB is set. For example, it is a voltage range of 3.0V to 4.2V. Battery voltage VB is boosted to boosted voltage VUP by booster circuit 20. The boosted voltage VUP is supplied as a power supply voltage for the amplifier 50. The reason why the battery voltage VB is boosted by the booster circuit 20 is that the battery voltage VB fluctuates due to fluctuations in the remaining battery level over time and usage. Since the booster circuit 20 outputs the boosted voltage VUP having a predetermined voltage value (for example, 8V) regardless of the variation of the voltage value of the battery voltage VB, it is convenient as the power supply voltage of the amplifier 50. As a power supply voltage for a CPU 30 and a DSP 40 described later, the boosted voltage VUP can be supplied as it is, or can be further stepped down to a lower voltage (for example, 3.3 V, 5.0 V, etc.) by a step-down power supply circuit (not shown). In some cases, power is also supplied.

  The battery voltage VB is input to an analog input port such as an AD conversion port of the CPU 30. The battery voltage VB is converted into a digital value inside the CPU 30, and then the processing described later in FIG. The clip level set for this processing is issued to the DSP 40 by the control signal CTL. The control signal CTL is a digital signal including other signals necessary for various controls in the DSP 40.

  The DSP 40 performs digital signal processing on the input audio signal AIN input from the input terminal IN. As normal signal processing, sound quality adjustment such as volume adjustment, equalization adjustment, and mixing adjustment is performed on the input audio signal AIN according to the control signal CTL from the CPU 30, and the output audio signal DA is output.

  The output audio signal DA is amplified by the amplifier 50 and output to the speaker 60 as the amplified audio signal DAA.

  Here, the DSP 40 is instructed to set the clip level by the control signal CTL output from the CPU 30. The clip level to be commanded is set by reducing the level according to the decrease in the battery voltage VB by the control described later with reference to the flowchart of FIG. As a result, the maximum clipped sound pressure level output from the speaker 60 becomes a voltage value that sequentially decreases from 8V, which is a voltage value in a state where clipping is not performed. For example, the amplitude of the maximum sound pressure level output from the speaker 60 is controlled with a voltage value of 5V to 8V.

  The clip level adjustment flow in the CPU 30 is shown in FIG. When the audio apparatus 1 is powered on and activated, the CPU 30 compares the voltage value of the battery voltage VB input to the AD conversion port with the first reference voltage V1. The first reference voltage V1 is, for example, a voltage value at which the battery voltage VB is close to the lower limit of the used battery voltage range (3.0V to 4.2V). For example, V1 = 3.2V.

  While the battery voltage VB is equal to or higher than the first reference voltage V1 (3.2 V) (S1: NO), the comparison operation is continued. When the battery voltage VB falls below the first reference voltage V1 (3.2 V) (S1: YES), a setting is made to decrease the clip level of the sound pressure level by a predetermined level (for example, 1 dB) (S3). As a result, the maximum sound pressure level is reduced to a clip level by a predetermined level, and the load current is reduced. As a result, the voltage drop due to the load current flowing through the output resistance of the battery 10 is reduced. The decrease in the battery voltage VB is suppressed, the voltage value is recovered, and increases from the first reference voltage V1 (3.2V).

  Next, the voltage value of the battery voltage VB is compared with the second reference voltage V2 (S5). Here, the second reference voltage V2 has a voltage value higher than the first reference voltage V1 (3.2V). The battery voltage VB is a voltage value at which sound output can be performed without reducing the clip level of a predetermined level in step (S3). The reference voltage is set with hysteresis with respect to the first reference voltage V1. For example, the voltage value is slightly higher than V1 = 3.2V, which is 3.4V (V2 = 3.4V).

  When the battery voltage VB exceeds the second reference voltage V2 (3.4V) (S5: YES), the clip level is added back by the level reduced in step (S3). Specifically, the clip level is increased by 1 dB (S7). In step (S3), the state before the clip level is reduced is restored.

  Conversely, when the battery voltage VB is equal to or lower than the second reference voltage V2 (3.4V) (S5: NO), the voltage value of the battery voltage VB is further compared with the third reference voltage V3 (S9). Here, the third reference voltage V3 has a voltage value lower than the first reference voltage V1 (3.2 V). The case where the battery voltage VB does not return to the voltage range of the used battery voltage range (3.0 V to 4.2 V) even if the clip level is reduced in step (S3) is shown. For example, V3 = 3.0V.

  When the battery voltage VB falls below the third reference voltage V3 (3.0 V) (S9: YES), even if the clip level is reduced in step (S3), the battery voltage VB is within the use battery voltage range (3.0 V to 4.V. 2V) is determined not to return to the voltage range, and the operation of the audio device 1 is stopped assuming that the remaining battery level is insufficient (S11). Conversely, if it is determined that the battery voltage VB is greater than or equal to the third reference voltage V3 (3.0V) (S9: NO), the battery voltage VB is in the voltage range of the used battery voltage range (3.0V to 4.2V). The process returns to step (S1), and the battery voltage VB comparison and detection process is continued.

  Here, the CPU 30 is an example of a control unit. In the flowchart of FIG. 2, the process of step (S1) is an example of the first comparison unit, the process of step (S5) is an example of the second comparison unit, and the process of step (S9) is the third comparison unit. It is an example of a means.

The effects of this embodiment will be described by taking an audio signal having a wide dynamic range such as classical music as an example of the input audio signal AIN. In an audio signal having a wide dynamic range, a period with a low sound pressure level and a period with a large sound pressure are mixed during sound output. When the sound pressure level is low, the load current accompanying the driving of the speaker 60 by the amplifier 50 is small, so that the decrease in the battery voltage is also small. Sound output along the original sound can be obtained.

  When the sound pressure level is high, the load current accompanying driving of the speaker 60 is large, so if the sound output along the original sound is output as it is, the battery voltage is greatly reduced. Even if the time during which sound with a large sound pressure level is output is a limited time of the entire output period, if the battery voltage VB falls below the operating battery voltage range (3.0 V to 4.2 V) during that period, the audio The device may be shut down due to power shortage. The apparatus shuts down due to a decrease in the battery voltage VB during a part of the entire output period, and the remaining battery charge may not be used up effectively. The continuous operation time with batteries must be short.

  In this regard, according to the present embodiment, the maximum sound pressure level is reduced by reducing the clip level according to the decrease in the battery voltage VB at the maximum sound pressure level at which the decrease in the battery voltage VB due to the load current is most significant. Thereby, since the load current at the maximum sound pressure level is reduced, it is possible to suppress a decrease in the battery voltage VB due to the load current. The battery voltage VB can be kept within the voltage range of the used battery voltage (3.0 V to 4.2 V) at the maximum sound pressure level at which the battery voltage drop is most noticeable, and the operation of the audio device 1 is continued. Can do. The continuous operation time of the audio apparatus 1 can be extended.

  Further, the clip level is adjusted by the digital signal processing of the DSP 40. Here, the DSP 40 is an essential configuration for the audio apparatus 1 that performs volume control, equalization adjustment, mixing adjustment, and the like, which are normal controls. The clip level can be adjusted using the DSP 40 which is an essential configuration, and there is no need to add a dedicated circuit configuration. The clip level of the sound pressure level can be adjusted without complicating the circuit configuration by adding a dedicated circuit and increasing the current consumption.

  Furthermore, the clip level can be finely adjusted by the digital signal processing of the DSP 40.

  In step (S1), the battery voltage VB is compared with the first reference voltage V1 (3.2V) to reduce the clip level. In step (S5), the battery voltage VB is changed to the second reference voltage V2 (3. 4V), the clip level is restored. As a result, at the maximum sound pressure level at which the load current becomes maximum, the reduction of the clip level can be minimized when the load current is suppressed and the decrease in the battery voltage VB is suppressed. A decrease in battery voltage VB can be suppressed while maintaining the sound quality at the maximum sound pressure level.

Needless to say, the present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the spirit of the present invention.
For example, in the embodiment, the configuration including the DSP 40 separately from the CPU 30 has been described, but the present application is not limited to this. It is also possible to adjust the functions of the DSP 40 with the CPU 30 without providing the DSP 40.
Moreover, in the flowchart of FIG. 2, although step (S9) was described as performing after step (S1) and (S5), this application is not limited to this. When determining in step (S1), the process in step (S9) can also be performed.
In the embodiment, the level at which the clip level is reduced is described as 1 dB, but the present application is not limited to this. The reduction width at the time of sequential reduction may be a width other than 1 dB, and the reduction width can be changed for each stage of clip level reduction. It is also possible to set the reduction range to be larger or smaller as it is reduced. It is also possible to adjust the clip level reduction width according to the detected voltage value of the battery voltage VB. That is, when the decrease in the battery voltage VB is large, the clip level reduction range is set to be large, and when the decrease in the battery voltage VB is small, the clip level reduction range is set to be small. it can.

1 Audio device 10 Battery 20 Booster circuit 30 CPU
40 DSP
50 Amplifier 60 Speaker IN Input Terminal AIN Input Audio Signal CTL Control Signal DA Output Audio Signal DAA Amplified Audio Signal V1 First Reference Voltage V2 Second Reference Voltage V3 Third Reference Voltage VB Battery Voltage VUP Boost Voltage

Claims (4)

An audio device driven by a battery,
A DSP that performs digital signal processing on an input audio signal;
An audio device comprising: a control unit configured to perform a setting for reducing a clip level for clipping a sound pressure level for the DSP according to a decrease in a battery voltage output from the battery. The controller is
First comparison means for comparing the battery voltage with a first reference voltage;
The clip level is set to a level obtained by subtracting a predetermined level from a preset level every time the first comparison means detects that the battery voltage is lower than the first reference voltage. 2. The audio device according to 1. The controller is
A second comparing means for comparing the battery voltage with a second reference voltage higher than the first reference voltage;
In response to detecting that the battery voltage exceeds the second reference voltage by the second comparing means, the clip level is returned to a level obtained by adding back the predetermined level just before the clip level. Item 3. The audio device according to Item 2. The controller is
A third comparing means for comparing the battery voltage with a third reference voltage lower than the first reference voltage;
The audio according to any one of claims 1 to 3, wherein an operation stop command is issued in response to detecting that the battery voltage is lower than the third reference voltage by the third comparing means. apparatus.

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