Music reproduction device

The present invention relates to a music playback device that outputs an audio signal to headphones.

In headphones used for listening to sound, the impedance differs depending on the headphones. Therefore, it is necessary to change the gain of the music playback device according to the impedance of the headphones. A technique for detecting the impedance of headphones is disclosed in order to automatically change the gain of a music player. Patent Document 1 discloses that a series resistor is provided in a signal line and the impedance of headphones is measured from the voltage of the resistor. Further, Patent Document 2 discloses that a DC voltage is applied from a headphone jack and the voltage of the headphone terminal is read by an A / D converter.

<p num="0003"><patcit num="1"><text>Japanese Patent No. 3659349</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2013-126142</text></patcit></p>

<p num="0004"> As described above, if a series resistor is provided in the audio signal line or an IC for impedance detection is provided, there is a problem that the sound quality deteriorates.</p><p num="0005"> An object of the present invention is to make it possible to detect the impedance of headphones without deteriorating the sound quality.</p><p num="0006"> The music playback device of the first invention includes an amplifier that amplifies an analog audio signal and outputs the amplified analog audio signal to connected headphones, a power supply that supplies a power supply voltage to the amplifier, and the power supply and the amplifier. It is characterized by including a resistor connected between the two, and a control unit that detects a voltage generated by the resistor when a test signal is input to the amplifier as an analog audio signal.</p><p num="0007"> In the present invention, the control unit detects the voltage generated by the resistor when the test signal is input to the amplifier as an analog audio signal. In addition, the impedance of the headphones can be calculated from the voltage generated by the resistor. In the present invention, the power supply line is provided with the detecting means for detecting the impedance of the headphones, and the audio signal line is not provided with the detecting means. As a result, the impedance of the headphones can be detected without deteriorating the sound quality.</p><p num="0008"> The music playback device of the second invention is the music playback device of the first invention, in which the control unit lowers the gain of the amplifier when the detected absolute value of the voltage is larger than the absolute value of a predetermined value. When the absolute value of the detected voltage is equal to or less than the absolute value of the predetermined value, the gain of the amplifier is set to high gain.</p><p num="0009"> In the present invention, the control unit sets the gain of the amplifier to low gain when the absolute value of the detected voltage is larger than the absolute value of the predetermined value. Further, the control unit sets the gain of the amplifier to high gain when the absolute value of the detected voltage is equal to or less than the absolute value of the predetermined value. Therefore, according to the present invention, the gain is set according to the impedance of the headphones.</p><p num="0010"> The music playback device of the third invention is the music playback device of the first invention, wherein the control unit calculates the impedance of the headphones based on the detected voltage.</p><p num="0011"> The music playback device of the fourth invention is the music playback device of the third invention, wherein the control unit sets the gain of the amplifier according to the calculated impedance.</p><p num="0012"> In the present invention, the control unit sets the gain of the amplifier according to the calculated impedance. Therefore, according to the present invention, the gain of the amplifier is set according to the impedance.</p><p num="0013"> The music playback device of the fifth invention further includes a D / A converter that D / A-converts a digital audio signal into an analog audio signal and outputs it to the amplifier in the music playback device of the third invention. Is characterized in that the volume of the D / A converter is set according to the calculated impedance.</p><p num="0014"> In the present invention, the control unit sets the volume of the D / A converter according to the calculated impedance. Therefore, according to the present invention, the volume of the D / A converter is set according to the impedance.</p><p num="0015"> The music playback device of the sixth invention further includes a power supply control circuit for controlling the power supply in the music playback device of the third invention, and the control unit uses the power supply control circuit according to the calculated impedance. It is characterized in that the power supply voltage supplied from the power supply is controlled.</p><p num="0016"> In the present invention, the control unit controls the power supply voltage supplied from the power supply by the power supply control circuit according to the calculated impedance. Therefore, according to the present invention, the power supply voltage corresponding to the impedance is supplied to the amplifier.</p><p num="0017"> The music playback device of the seventh invention is the music playback device of any of the first to sixth inventions, wherein the test signal is a triangular wave having a predetermined frequency or less.</p><p num="0018"> In the present invention, since the test signal has a predetermined frequency or less, sound leakage from the headphones is unlikely to occur while measuring the impedance of the headphones. Moreover, since the test signal is a triangular wave, it is easy to detect the peak level of the voltage generated by the resistor.</p><p num="0019"> The music playback device of the eighth invention is the music playback device of any one of the first to seventh inventions, and the test signal has the same integral value on the positive side and the integral value on the negative side. It is characterized by.</p><p num="0020"> In the present invention, the test signal has the same integral value on the positive side and the integral value on the negative side. That is, since the positive side and the negative side are symmetrical signals, the load on the power supply immediately after the test becomes uniform. This prevents offsetting of the power supply voltage.</p><p num="0021"> The music playback device of the ninth invention is the music playback device of any one of the first to eighth inventions, one end of which is connected between the resistor and the amplifier, and the other end of which is connected to the ground potential. A capacitor for decoupling is further provided, and the resistor is for decoupling.</p><p num="0022"> In the present invention, a resistor for decoupling is used as a resistor for impedance detection. Therefore, it is not necessary to add new parts for detecting the impedance of the headphones.</p><p num="0023"> The music playback device of the tenth invention is characterized in that the frequency of the test signal is lower than the cutoff frequency of the capacitor in the music playback device of the ninth invention.</p><p num="0024"> In the present invention, the frequency of the test signal is lower than the cutoff frequency of the capacitor. Therefore, the test signal is not affected by the decoupling capacitor.</p>

<p num="0025"> According to the present invention, the impedance of headphones can be detected without deteriorating the sound quality.</p>

<figref num="1">It is a block diagram which shows the structure of the digital audio player which concerns on embodiment of this invention.</figref><figref num="2">It is a figure which shows the amplifier and its peripheral circuit.</figref><figref num="3">It is a graph which shows the test signal.</figref><figref num="4">It is a figure which shows the amplifier and its peripheral circuit.</figref><figref num="5">It is a graph which shows the voltage generated by a resistor.</figref><figref num="6">It is a flowchart which shows the processing operation of DAP when measuring the impedance of a headphone.</figref><figref num="7">It is a figure which shows the amplifier and its peripheral circuit.</figref><figref num="8">It is a figure which shows the amplifier and its peripheral circuit.</figref>

Hereinafter, embodiments of the present invention will be described. FIG. 1 is a block diagram showing a configuration of a digital audio player (hereinafter, referred to as DAP) according to an embodiment of the present invention. DAP1 (music playback device) outputs analog audio data (analog audio signal) to the headphones 101. The headphone 101 outputs audio to the outside based on analog audio data.

As shown in Fig. 1, DAP1 includes CPU2, storage unit 3, display unit 4, operation unit 5, DSP6, D / A converter (hereinafter referred to as "DAC") 7, amplifier 8, wireless module 9, and USB interface. (Hereafter, it is called "USB I / F".) It is equipped with 10.

The CPU (Central Processing Unit) 2 (control unit) controls each part that constitutes DAP1 according to the control program, OS program, and application program. The storage unit 3 stores various data such as RAM (Random Access Memory) that functions as the main memory of CPU 2, ROM (Read Only Memory) that stores control programs, programs such as OS programs and application programs, and digital audio data. It consists of flash memory. The storage unit 3 is not limited to the configuration illustrated, and may include an HDD (Hard Disk Drive) or the like.

The display unit 4 displays various images (including still images and moving images), and is composed of a liquid crystal panel. The operation unit 5 includes operation keys for performing various settings and a touch panel linked with the display unit 4. The user can input various characters, make settings, and the like via the operation unit 5. In addition, the user can set DAP1 to the impedance measurement mode for measuring the impedance of the headphones 101 via the operation unit 5. The CPU 2 accepts the impedance measurement mode setting via the operation unit 5.

The DSP (Digital Signal Processor) 6 performs signal processing such as equalizer processing on digital audio data. The DAC7 D / A converts digital audio data (digital audio signal) into analog audio data (analog audio signal). The amplifier 8 amplifies the analog audio data D / A-converted by the DAC 7, and outputs the analog audio data to the headphones 101. The wireless module 9 is for performing wireless communication in accordance with the Bluetooth (registered trademark) standard and the Wi-Fi standard. The USB I / F10 is for communicating according to the USB standard.

FIG. 2 is a diagram showing an amplifier and its peripheral circuits. As shown in FIG. 2, the DAP1 further includes power supplies V1, V2, resistors R1 to R4, and capacitors C1 and C2. In FIG. 2, the headphone 101 is shown as a load resistance RL. The power supply V1 supplies the positive power supply voltage to the amplifier 8. The power supply V2 supplies the negative power supply voltage to the amplifier 8. The resistor R1 is connected between the power supply V1 and the amplifier 8. The resistor R2 is connected between the power supply V2 and the amplifier 8. The resistors R1 and R2 are resistors for decoupling, but also serve as resistors for impedance detection of the headphone 101.

One end of resistor R3 is connected to the output terminal of amplifier 8. The other end of the resistor R3 is connected to the non-inverting input terminal of the amplifier 8 and one end of the resistor R4. One end of the resistor R4 is connected to the non-inverting input terminal of the amplifier 8 and the other end of the resistor R3. The other end of the resistor R4 is connected to the ground potential. Capacitors C1 and C2 are capacitors for decoupling. One end of the capacitor C1 is connected between the resistor R1 and the amplifier 8. The other end of the capacitor C1 is connected to the ground potential. One end of the capacitor C2 is connected between the resistor R2 and the amplifier 8. The other end of the capacitor C2 is connected to the ground potential.

When the CPU 2 accepts the impedance measurement mode setting, it inputs a test signal to the non-inverting input terminal of the amplifier 8. FIG. 3 is a graph showing the test signal. As shown in FIG. 3, the test signal is a triangular wave. Further, in the test signal, the integrated value (area) on the positive side and the integrated value (area) on the negative side are the same. The frequency of the test signal is lower than the cutoff frequency of the capacitors C1 and C2 (below a predetermined frequency).

CPU2 detects the voltage generated by resistors R1 and R2 when the test signal is input to amplifier 8. Since the voltage detection on the positive side and the voltage detection on the negative side have the same configuration, only the voltage detection on the positive side will be described. As shown in FIG. 4, the CPU 2 detects the voltage generated by the A / D-converted resistor R1 by the A / D converter 11.

FIG. 5 is a graph showing the voltage generated by the resistor R1. The voltages are shown when the impedance of the headphones is 16Ω, 32Ω, 60Ω, 100Ω, 300Ω, and 10kΩ, respectively. In the present embodiment, the CPU 2 sets the gain of the amplifier 8 to low gain when the absolute value of the detected voltage (peak level) is larger than 17 mV (absolute value of a predetermined value). Further, the CPU 2 sets the gain of the amplifier 8 to a high gain when the absolute value of the detected voltage is 17 mV or less. In the case of voltage detection on the negative side, the predetermined value is -17 mV, and the absolute value of the predetermined value is 17 mV.

Next, the processing operation of DAP1 when measuring the impedance of the headphones will be described with reference to the flowchart shown in FIG. CPU2 determines whether or not the impedance measurement mode setting has been accepted (S1). While it is determined that the impedance measurement mode setting is not accepted, CPU2 repeatedly executes the determination of S1 (S1: No). When CPU2 determines that the impedance measurement mode setting has been accepted (S1: Yes), it generates a test signal (S2). Next, CPU2 measures the voltage generated at resistors R1 and R2 due to the power supply current (S3). The CPU 2 measures the generated voltage obtained by the A / D converter 11 after A / D conversion. Next, CPU2 determines whether the measured absolute value of the voltage V is greater than 17 mV (S4). When CPU2 determines that the absolute value of the measured voltage V is greater than 17 mV (S4: Yes), it sets the gain of amplifier 8 to low gain (S5). On the other hand, when CPU2 determines that the absolute value of the measured voltage V is not greater than 17 mV, that is, the absolute value of the measured voltage V is 17 mV or less (S4: No), the gain of the amplifier 8 is set to high gain. Set (S6).

As described above, in the present embodiment, the CPU 2 detects the voltage generated by the resistors R1 and R2 when the test signal is input to the amplifier 8 as analog audio data. Further, the impedance of the headphone 101 can be calculated from the voltage generated by the resistors R1 and R2. In the present embodiment, the detection means for detecting the impedance of the headphone 101 is provided only in the power supply line, and the detection means is not provided in the audio signal line. As a result, the impedance of the headphone 101 can be detected without deteriorating the sound quality.

Further, in the present embodiment, the CPU 2 sets the gain of the amplifier 8 to low gain when the absolute value of the detected voltage is larger than the absolute value (17 mV) of the predetermined value. Further, the CPU 2 sets the gain of the amplifier 8 to high gain when the absolute value of the detected voltage is equal to or less than the absolute value (17 mV) of the predetermined value. Therefore, according to the present embodiment, the gain is set according to the impedance of the headphones 101.

Further, in the present embodiment, since the test signal has a predetermined frequency or less (lower than the cutoff frequency of the capacitors C1 and C2), sound leakage from the headphone 101 is unlikely to occur while measuring the impedance of the headphone 101. .. Moreover, since the test signal is a triangular wave, it is easy to detect the peak level of the voltage generated by the resistors R1 and R2.

Further, in the present embodiment, the test signal has the same integrated value on the positive side and the integrated value on the negative side. That is, since the positive side and the negative side are symmetrical signals, the load on the power supplies V1 and V2 immediately after the test becomes uniform. This prevents offsetting of the power supply voltage.

Further, in the present embodiment, the resistors R1 and R2 for decoupling are used as the resistors R1 and R2 for impedance detection. Therefore, it is not necessary to add new parts for impedance detection of the headphone 101.

Further, in the present embodiment, the frequency of the test signal is lower than the cutoff frequency of the capacitors C1 and C2. Therefore, the test signal is not affected by the decoupling capacitors C1 and C2.

Although the embodiments of the present invention have been described above, the embodiments to which the present invention can be applied are not limited to the above-described embodiments, and as illustrated below, appropriate as long as the gist of the present invention is not deviated. It is possible to make changes.

In the above embodiment, the CPU 2 sets the gain of the amplifier 8 to low gain when the absolute value of the detected voltage is larger than the absolute value (17 mV) of the predetermined value. Further, the CPU 2 sets the gain of the amplifier 8 to high gain when the absolute value of the detected voltage is equal to or less than the absolute value (17 mV) of the predetermined value. Instead of this, the CPU 2 may calculate the impedance of the headphone 101 based on the detected voltage and perform the subsequent processing. For example, as shown in FIG. 5, if the peak voltage level is 23 mv, the impedance of the headphones 101 is 32 Ω. The CPU2 can calculate the impedance of the headphone 101 from the correspondence between the peak level of the voltage and the impedance.

The CPU 2 may set the gain of the amplifier 8 according to the calculated impedance. As a result, the gain of the amplifier 8 is set according to the impedance.

Further, as shown in FIG. 7, the CPU 2 may set the volume of the DAC 7 according to the calculated impedance. As a result, the volume of the DAC 7 is set according to the impedance.

Further, as shown in FIG. 8, the CPU 2 controls the power supply voltage supplied from the power supplies V1 and V2 by the power supply control circuit 12 that controls the power supplies V1 and V2 according to the calculated impedance. As a result, the power supply voltage corresponding to the impedance is supplied to the amplifier 8.

As described above, the CPU 2 can calculate the impedance of the headphone 101 from the correspondence between the peak voltage level and the impedance. Not limited to this, the time until the voltage generated by the resistors R1 and R2 reaches a predetermined value is measured by a counter or the like, and the CPU2 may calculate the impedance based on this.

In the above-described embodiment, DAP is exemplified as a music playback device. Not limited to this, it may be a smartphone, a tablet PC, a USB DAC, or the like.

The present invention can be suitably adopted in a music playback device that outputs an audio signal to headphones.

1 DAP (Music Player) 2 CPU (control unit) 7 DAC (D / A converter) 8 amplifier 11 A / D converter 12 Power control circuit C1, C2 capacitors R1, R2 resistors V1, V2 power supply 101 headphones