JP4946644B2 - Balanced output apparatus and method - Google Patents

Description

  The present invention relates to a balanced output apparatus and method for amplifying an analog balanced input by a pair of amplifiers and extracting an analog balanced output.

  For example, an audio output circuit that converts a digital audio signal into an analog balanced output, converts the digital audio signal into an analog balanced output, amplifies it, and extracts it as a speaker monitor output is known. .

  For such analog balanced output from the amplification output circuit, one end of the output may be grounded depending on the monitor device to be used and the usage pattern. In addition, one or both ends of the analog balanced output may be grounded due to an accident or the like.

  FIG. 5 shows an example of an amplification output circuit as such an audio monitor output circuit. One (+ side) and the other (− side) digital audio signals corresponding to analog balanced output are connected to terminals 101 and 102, respectively. To the D / A converters 103 and 104 of the analog output circuit 100, respectively. The D / A converters 103 and 104 convert the input digital audio signal into two analog signals of +/− as analog balanced outputs and output them. Analog balanced outputs from the D / A converters 103 and 104 are amplified by the amplifiers 105 and 106, respectively, and taken out from the output terminals 109 and 110 via the resistors 107 and 108, respectively.

  In FIG. 5, so-called “blank” connection is made such that the output from the resistor 107 is fed back to the amplifier 106, and the output from the resistor 108 is fed back to the amplifier 105. Here, when one end (for example, the output terminal 110) of the output terminal is grounded, the output level is lowered by feeding back and canceling the opposite side of the analog balanced output. That is, when the output terminal 110 is grounded and the level is lowered, this is fed back to the amplifier 105, the output level of the amplifier 105 is increased, and this is fed back to the amplifier 106. Therefore, the output level of the amplifier 106 is further lowered, and finally Specifically, the output level of the amplifier 106 approaches 0 level, and the output level of the amplifier 105 is approximately twice that at the normal time (when not grounded). This realizes output protection and output level maintenance when the output terminal is grounded.

  As a conventional technique, Patent Document 1 describes a muting circuit that mutes an output signal of audio or the like with high power.

JP-A-9-238029

  By the way, when the analog feedback configuration as described above is used to protect the analog balanced output, there are the following problems.

  That is, in the case of analog feedback, the phase characteristics are not good, the output level is not stable due to variations in the elements such as the resistors 107 and 108, the level and phase depend on the accuracy of the elements, the balance of balanced output and There is a drawback that the phase difference deteriorates.

  Further, in the analog feedback configuration as shown in FIG. 5, for example, a loop of resistor 107 → amplifier 106 → resistor 108 → amplifier 105 is formed from the resistor 107 on the output side of the amplifier 105, so that no grounding occurs. Even when the output levels of the D / A converters 103 and 104 are uniform at the time of normal balanced output, the higher the frequency, the more the phase difference occurs between the balanced outputs due to variations in the degree of amplification and phase compensation. The degree gets worse.

  In recent years, a wideband audio signal exceeding the sound quality of a normal CD has been known. In the case of an analog balanced output circuit for monitoring such a wideband audio signal, a good phase characteristic or A stable output level is required. For this reason, the analog feedback configuration as described above is not suitable for a broadband balanced output.

  The present invention has been proposed in view of such a conventional situation, and provides an analog balanced output having good phase characteristics and a stable output level for monitoring a wideband audio signal, and an analog balanced output. An object of the present invention is to provide a balanced output device and method capable of reducing the output level when the ground is grounded to protect the output and suppress the generation of heat.

In order to solve the above-mentioned problems, the present invention D / A converts digital data output means for outputting digital balanced output data for analog balanced output and balanced output data from the digital data output means. A D / A converter, a pair of amplifiers for amplifying the balanced output from the D / A converter, and a pair of resistors connected in series to the signal lines of the analog balanced output from the pair of amplifiers, A pair of A / D conversion means for A / D converting the voltages at both ends of the pair of resistors, and a level difference between both ends of each resistance based on data from the pair of A / D conversion means is a predetermined set value. A pair of discriminating means to be compared with each other, and the level of the balanced output data of the digital data output means is controlled according to the discriminant outputs from the pair of discriminating means Possess a level control means for said level control means, the level difference attenuates the input level to the amplifier connected to the resistance it is determined to exceed the predetermined set value by a predetermined value by said judging means The level of the balanced output data is controlled as described above, and when it is determined that the level difference between both ends of the resistance determined to exceed the predetermined set value has returned below the predetermined set value by the determining means, The level of the balanced output data is controlled so that the input level to the amplifier is returned to the level at the time of normal balanced output.

Here, the level control means is configured such that the level difference is less than or equal to the predetermined set value by the determination means with respect to one resistance for which the level difference has been determined to exceed the predetermined set value by the determination means. It is preferable to control the level of the balanced output data so that the input level to the amplifier connected to the other resistance determined to be increased is increased by a predetermined value.

In order to achieve the above object, the present invention provides a balanced output method in which analog balanced inputs are amplified by a pair of amplifiers and are taken out as analog balanced outputs, respectively. A detection step for detecting a level difference between both ends of a pair of resistors connected in series, and a determination step for comparing the level difference between both ends of each resistor detected by the pair of level detection steps with a predetermined set value, respectively; depending on the respective determination output discriminated by the discrimination step possess a level control step of controlling the respective input levels of the pair of amplifiers, in the level control step, the level difference by the determination step is above a predetermined In order to attenuate the input level to the amplifier connected to the resistor determined to have exceeded the set value of The level of output data is controlled, and when it is determined that the level difference between both ends of the resistor determined to exceed the predetermined set value has returned to the predetermined set value or less by the determining step, the input to the amplifier The level of the balanced output data is controlled so that the level is returned to the level at the normal balanced output.

  According to the present invention, the level difference between both ends of the pair of resistors connected in series to the signal lines of the analog balanced output from the pair of amplifiers is compared with a predetermined set value, respectively, and the above-described difference is determined according to each comparison result. By controlling the input level of each pair of amplifiers, when the analog balanced output is grounded, the output level is lowered to protect the output and suppress the generation of heat. It is possible to improve characteristics such as phase difference and balance in a wide band.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram schematically showing an analog balanced output device for audio monitor output used in an embodiment of the present invention.

  In FIG. 1, an audio monitor output data generation unit 11 that generates digital audio monitor output data to be extracted as a speaker monitor output is included in a digital audio data processing circuit 1 configured by, for example, a so-called FPGA (Field Programmable Gate Array). Is provided. The audio monitor output data from the audio monitor output data generation unit 11 is sent to the monitor data output unit 10 and is used as output data on the non-inversion side (+ side) as it is, or on the inversion side (− side) via the inversion circuit 12. Used as output data. The non-inverted (+) output data from the audio monitor output data generation unit 11 is sent to the selected terminal a of the changeover switch 13 and to the selected terminal b of the changeover switch 13 via the attenuator 15. . The attenuator 15 attenuates input audio data by a predetermined amount (for example, −24 dB). The inversion side (-side) output data from the inverting circuit 12 is sent to the selected terminal a of the changeover switch 14 and to the selected terminal b of the changeover switch 14 via the attenuator 16.

  The non-inverted side (+ side) output data from the changeover switch 13 is sent to the D / A converter 21 of the analog output circuit 20, converted into an analog signal, amplified by the amplifier 23, and non-inverted of the analog balanced output. Side (+ side) output signal, which is further taken out from the output terminal 27 via the resistor 25. Further, the inverted (−) output data from the changeover switch 14 is sent to the D / A converter 22 of the analog output circuit 20 to be converted into an analog signal, amplified by the amplifier 24, and inverted of the analog balanced output. Side (−) output signal, and is further taken out from the output terminal 28 via the resistor 26. Here, the amplifiers 23 and 24 are, for example, line-out amplifiers or line amplifiers.

  The A / D converter 31 detects the terminal voltage of the resistor 25 inserted and connected to the output signal line of the amplifier 23 on the non-inverting side (+ side) of the analog balanced output and converts it into digital data. sending. The discriminator 33 compares the level difference (qp) between both terminals of the resistor 25 with a predetermined level setting value (for example, 6 dB), and switches and connects the changeover switch 13 according to the discrimination result. When the level difference (qp) is larger than the predetermined level setting value (for example, qp> 6 dB), it is determined that the corresponding non-inverted (+) output terminal 27 of the analog balanced output is grounded. The discrimination output from the device 33 becomes active, and the changeover switch 13 is switched and connected to the selected terminal b side. When the level difference (qp) between both terminals of the resistor 25 is less than or equal to a predetermined level setting value (6 dB), the discrimination output from the discriminator 33 is inactive, and the changeover switch 13 is connected to the selected terminal a side. It is in the state.

  Similarly, the inter-terminal pressure of the resistor 26 inserted and connected to the output signal line of the amplifier 24 on the inverting side (− side) of the analog balanced output is detected by the A / D converter 32 and converted into digital data for discrimination. The discriminator 34 selects the switch 14 when the level difference (qp) between both terminals of the resistor 26 is larger than a predetermined level setting value (6 dB) (qp> 6 dB). When it is 6 dB or less on the terminal b side, it is switched and connected to the selected terminal a side.

  In a normal balanced output state (normal state) in which neither of the output terminals 27 and 28 is grounded (or short-circuited), the level difference (qp) between both terminals of the resistors 25 and 26 is 6 dB. The change-over switches 13 and 14 are both connected to the selected terminal a. On the other hand, as shown in the example of FIG. 1, when the output terminal 28 on the inverting side (− side) of the analog balanced output is grounded (short-circuited), the level difference between both terminals of the resistor 25 is The discriminator 34 switches and connects the changeover switch 14 to the selected terminal b side. At this time, the inverting side (− side) output data attenuated by, for example, 24 dB from the inverting circuit 12 via the attenuator 16 is converted to the D / A converter 22 of the analog output circuit 20 via the selected terminal b of the changeover switch 14. Sent to. Accordingly, since the input to the inverting (−) amplifier 24 of the analog output circuit 20 is attenuated by 24 dB compared to the normal state, the amplifier 24 is protected so as not to pass an overcurrent to suppress the generation of heat. Can do.

  Here, the input level of the amplifier 24 is attenuated by a predetermined amount (for example, −24 dB) by the attenuator 16 without dropping the grounded (short-circuited) side output level of the analog balanced output to 0. After the attenuation, when the ground (short circuit) state of the output terminal 28 is released, the terminal voltage of the resistor 26 is detected by the A / D converter 32, and the detected level difference (qp) is 6 dB or less. This is because the changeover switch 14 is switched and connected to the selected terminal a side to be restored by detecting the occurrence of this. The same applies to the attenuator 15. In this way, if the gain on the grounded side is reduced, the analog balanced output's grounded side is not muted, so that it can be restored to its original normal level. It is preferable that the amplifier is attenuated to such an extent that no load is applied and the level can be determined. In this case, the level at the time of discrimination in the discriminators 33 and 34 so that the switching operation does not occur frequently due to the detected level difference (qp) fluctuating up and down with a predetermined value (for example, 6 dB) as a threshold value. As the difference (q−p), it is preferable to use the maximum value or effective value of the level at a certain time.

  FIG. 2 shows the phase difference between analog balanced outputs at the time of normal balanced output (normal state) in which grounding (short circuit) does not occur in the case of the embodiment shown in FIG. 1 of the present invention (curves A, A ′). And the conventional case shown in FIG. 5 (curves B and B ′). When an analog feedback configuration such as the conventional audio monitor output circuit shown in FIG. 5 is used, a loop such as the resistor 107 → the amplifier 106 → the resistor 108 → the amplifier 105 on the output side of the amplifier 105 is formed. As shown by the curves B and B ′ in FIG. 2 due to variations in the degree of amplification and components used for phase compensation even when the output levels of the D / A converters 103 and 104 are uniform in a normal state where no grounding occurs. As the frequency becomes higher, a phase difference occurs between the balanced outputs, and the degree of balance becomes worse. On the other hand, in the embodiment of the present invention as shown in FIG. 1, since the loop as described above does not exist, the balance depends only on the phase accuracy of each output circuit, and the curve A, FIG. As indicated by A ′, the phase difference is small even at a high frequency, and a good balance is maintained. Therefore, according to the embodiment of the present invention, for example, it is suitable for the purpose of obtaining an analog balanced output when monitoring a wide-band, high-quality audio signal exceeding the sound quality of a normal CD.

  By the way, in the above embodiment, the terminal voltages at both ends of the resistors 25 and 26 are converted into digital data by the A / D converters 31 and 32, and the level difference (q −p) is obtained and compared with a predetermined set value (6 dB). In the A / D converters 31 and 32, the level difference (qp) is obtained and the digital data is determined by the discriminators 33 and 34. You may make it send to. Furthermore, as described above, the A / D converters 31 and 32 obtain the level difference using the maximum value or effective value of the level in a certain time and send the digital data to the discriminators 33 and 34. Good. Further, the predetermined set value at the time of level comparison in the discriminators 33 and 34 is not limited to 6 dB, and the attenuation amount in the attenuators 15 and 16 is not limited to -24 dB.

  Next, FIG. 3 shows a case where the analog balanced output level is maintained when grounding (short circuit) occurs as another embodiment of the present invention. That is, in the embodiment of FIG. 1, the output level on one side where grounding occurs is attenuated and the output level on the other side is not changed as it is. However, in the example of FIG. The difference between the output level at the time of normal balanced output is reduced by increasing (for example, doubling) the output level on the non-existing side.

  3, parts corresponding to those in FIG. 1 are given the same reference numerals, and level amplifiers 35 and 36, changeover switches 37 and 38, and parts similar to those in FIG. Selection controllers 39 and 40 are added. That is, the audio monitor output data from the audio monitor output data generation unit 11 is sent not only to the attenuator 15 but also to the selected terminal a of the level amplifier 35 and the changeover switch 37, and the output from the changeover switch 37 is changed to the changeover switch 13. To the selected terminal a. The output from the level amplifier 35 is sent to the selected terminal b of the changeover switch 37, and the changeover switch 37 is controlled to be changed by the selection controller 39. The selection controller 39 is supplied with the discrimination output from the discriminator 33 to the negative (N) input terminal and the discrimination output from the discriminator 34 to the affirmative (Y) input terminal. An enable (+ 6dB Enable) signal is supplied. Similarly, the data from the inverting circuit 12 is sent to the selected terminal a of the attenuator 16, the level amplifier 36 and the changeover switch 38, and the output from the changeover switch 38 is sent to the selected terminal a of the changeover switch 14. ing. The output from the level amplifier 36 is sent to the selected terminal b of the changeover switch 38, and the changeover switch 38 is controlled by the selection controller 40. The selection controller 40 is supplied with the discrimination output from the discriminator 34 to the negative (N) input terminal and the discrimination output from the discriminator 33 to the positive (Y) input terminal, respectively, and the level amplification enable ( + 6dB Enable) signal is being supplied.

  The example of FIG. 3 shows the case where only the output terminal 28 on the inverting (−) output side of the analog balanced output is grounded (short-circuited) as in FIG. The level difference (qp) obtained by detecting the voltage with the A / D converter 32 exceeds 6 dB, and the discrimination output of the discriminator 34 becomes active. The discrimination output (active) of the discriminator 34 is sent to the change-over switch 14 so that the change-over switch 14 is switched and connected to the selected terminal b side, and the positive (Y) input terminal of the discriminator 39 and the discriminator 40. Is sent to the negative (N) input terminal. The discrimination output of the discriminator 33 is inactive, and the changeover switch 13 remains connected to the selected terminal a. In the selection controller 39, the discrimination output input to the negative (N) input terminal from the discriminator 33 is inactive, the discrimination output input to the positive (Y) input terminal from the discriminator 34 is active, and the terminal 41 When the level amplification enable (+6 dB Enable) signal from is turned on, the changeover switch 37 is connected to the selected terminal b side. In other conditions, the changeover switch 37 is connected to the selected terminal a side. Has been. Similarly, for the selection controller 40, the discrimination output input to the negative (N) input terminal is inactive, the discrimination output input to the positive (Y) input terminal is active, and the level amplification enable from the terminal 42 When the (+6 dB Enable) signal is in an effective state, the changeover switch 38 is connected to the selected terminal b, and the changeover switch 38 is connected to the selected terminal a under other conditions.

  Here, in the example of FIG. 3, it is assumed that the level amplification enable (+6 dB Enable) signal from the terminals 41 and 42 is in an effective state, and the selection controller 39 switches and connects the changeover switch 37 to the selected terminal b side. To do. Accordingly, the output from the level amplifier 35 is sent to the D / A converter 21 of the analog output circuit 20 via the selected terminal b of the changeover switch 37 and via the selected terminal a of the changeover switch 13 and sent to the analog signal. Is input to the amplifier 23. If the amplification factor (gain) of the level amplifier 35 is +6 dB, the input level input to the amplifier 23 is twice that of the normal state (during normal balanced output that is not grounded), and the analog balanced output extracted from the output terminal 27. The level of the non-inverted (+) output signal is doubled. Therefore, even if the output level on the grounded side is approximately 0, the output level on the ungrounded side is doubled. Therefore, the output level between both ends of the analog balanced output is shown in FIG. Similar to the conventional configuration, even when grounding occurs, the same output level as in the normal state can be obtained.

  Next, FIG. 4 shows a specific example in which the embodiment shown in FIG. 1 of the present invention is applied to a stereo left and right channel monitor output circuit.

  In FIG. 4, the digital audio data processing circuit 1 includes a left (L) channel audio monitor output data generator 11L that generates digital audio monitor output data to be extracted as stereo left and right channel speaker monitor outputs, An audio monitor output data generation unit 11R for the right (R) channel is provided. Each data from these audio monitor output data generation units 11L and 11R is sent to monitor data output units 10L and 10R for stereo left and right channels, respectively, and each output data from these monitor data output units 10L and 10R is The signals are sent to analog output circuits 20L and 20R for stereo left and right channels, respectively.

  The stereo left (L) channel monitor data output unit 10L includes a gain control unit 45 to which data from the left (L) channel audio monitor output data generation unit 11L is input. 1 is sent to a circuit unit comprising an inverting circuit 12, changeover switches 13 and 14, and attenuators 15 and 16 having the same configuration as in FIG. The changeover switches 13 and 14 are controlled to be switched by the discriminators 33 and 34, respectively. Since the inverting circuit 12, the changeover switches 13 and 14, the attenuators 15 and 16, and the discriminators 33 and 34 are the same as those in FIG. However, in the configuration of FIG. 4, the pair of digital balanced output data from the changeover switches 13 and 14 is multiplexed by the multiplexer 46 and sent to the analog output circuit 20L for the left (L) channel of the stereo as serial data. . The discrimination outputs from the discriminators 33 and 34 are sent to the gain control unit 45 and taken out as a status signal. The gain control unit 45 controls the gain of data from the audio monitor output data generation unit 11L in accordance with the discrimination output from the discriminators 33 and 34.

  The stereo left (L) channel analog output circuit 20L includes a D / A converter 29 to which serial digital balanced output data is supplied from the multiplexer 46 of the monitor data output unit 10L. Each output of the non-inverting side (+ side) and the inverting side (− side) of the analog balanced output is sent from the device 29 to the buffer amplifiers 51 and 52 (for example, as differential outputs, respectively). The outputs from the buffer amplifiers 51 and 52 are respectively sent to the line-out amplifiers 23 and 24 as shown in FIG. 1 and supplied as differential inputs of the differential amplifier 53. The resistors 25 and 26 and the A / D converters 31 and 32 after the line-out amplifiers 23 and 24 are the same as those in FIG. The analog balanced output for the left (L) channel is taken out from the output terminals 27L and 28L. A muting relay 54 is connected between the output terminals 27L and 28L.

  The output from the differential amplifier 53 of the analog output circuit 20L for the left (L) channel is sent to the variable resistor (so-called volume) 62 via the buffer 61L for the left (L) channel of the headphone monitor output circuit 60. Then, the volume of the headphone is adjusted and taken out from the left (L) channel headphone output terminal 65L via the left (L) channel buffer 63L and the headphone drive amplifier 64L.

  The stereo right (R) channel monitor data output unit 10R and analog output circuit 20R have the same configuration as the stereo left (L) channel monitor data output unit 10L and analog output circuit 20L described above. Therefore, the description is omitted. The analog balanced output for the right (R) channel of the stereo is taken out from the output terminals 27R and 28R of the analog output circuit 20R for the right (R) channel. Further, the output from the differential amplifier of the analog output circuit 20R for the right (R) channel is sent to the variable resistor (so-called volume) 62 via the buffer 61R for the right (R) channel of the headphone monitor output circuit 60. The volume is adjusted and taken out from the right (R) channel headphone output terminal 65R via the right (R) channel buffer 63R and the headphone drive amplifier 64R.

  According to the embodiment of the present invention as described above, it is detected that the analog balanced output is grounded, the output level is lowered to protect the output and suppress the generation of heat, and the normal balanced that is not grounded. Characteristics such as output phase difference and balance can be improved.

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  For example, the A / D converters 21 and 22 obtain the level difference between the resistors 25 and 26, or obtain the level difference using the maximum value or effective value of the level in a certain time, and the digital data is determined by the discriminator 33, 34 may be sent. Further, the predetermined set value for level comparison in the discriminators 33 and 34 is not limited to 6 dB, and the attenuation amount in the attenuators 15 and 16 is not limited to -24 dB.

It is a block diagram which shows the structural example of the analog balanced output device for audio monitor output used as embodiment of this invention. It is a graph which shows the phase difference between the analog balanced outputs at the time of the normal balanced output in which the ground is not generated for the embodiment of the present invention and the conventional example. It is a block diagram which shows the structural example of the analog balanced output device of other embodiment of this invention. It is a block diagram which shows the specific example which applied the analog balanced output device of embodiment of FIG. 1 of this invention to the monitor output circuit of the stereo left-right channel. It is a block diagram which shows an example of the analog balanced amplification output circuit as a conventional audio monitor output circuit.

Explanation of symbols

  10, 10A, 10L, 10R monitor data output unit, 11, 11L, 11R audio monitor output data generation unit, 12 inversion circuit, 13, 14, 37, 38 changeover switch, 15, 16 attenuator, 21, 22, 29 D / A converter, 23,24 amplifier, 25,26 resistor, 27,28,27L, 28L, 27R, 28R output terminal, 31,32 A / D converter, 33,34 discriminator, 35,36 level amplifier, 39, 40 selection controller

Claims (6)

Digital data output means for outputting digital balanced output data for analog balanced output;
D / A conversion means for D / A converting each of the balanced output data from the digital data output means;
A pair of amplifiers for respectively amplifying the balanced outputs from the D / A conversion means;
A pair of resistors connected in series to each signal line of the analog balanced output from the pair of amplifiers;
A pair of A / D conversion means for A / D converting the voltage across the pair of resistors, respectively;
A pair of discriminating means for comparing a level difference between both ends of each resistor based on data from the pair of A / D conversion means with a predetermined set value;
It possesses a level control means for controlling the level of balanced output data of the digital data output means in accordance with respective determination outputs from the pair discriminating means,
The level control means adjusts the level of the balanced output data so as to attenuate the input level to the amplifier connected to the resistor determined that the level difference has exceeded the predetermined set value by the determination means by a predetermined value. When the level difference between both ends of the resistance determined to have exceeded the predetermined set value is returned to the predetermined set value or less by the determining means, the input level to the amplifier is adjusted to a normal balanced level. A balanced output device for controlling the level of the balanced output data so as to return to the level at the time of output. The level control means determines that the level difference is less than or equal to the predetermined set value by the determination means for one resistance for which the level difference has been determined to exceed the predetermined set value by the determination means. have been other balanced output apparatus according to claim 1, wherein that controls the level of the balanced output data so as to increase by a predetermined value the input level to connect the resistor to the amplifier. It said determination means, balanced output apparatus according to claim 1, wherein the level difference based on the maximum value or the effective value of the level at a certain time at both ends of the resistor you compared with the predetermined set value. In the balanced output method in which the analog balanced input is amplified by a pair of amplifiers and taken out as an analog balanced output,
A detecting step for detecting a level difference between both ends of a pair of resistors connected in series to each signal line of the analog balanced output from the pair of amplifiers;
A determination step of comparing a level difference between both ends of each resistor detected by the pair of level detection steps with a predetermined set value, respectively;
Depending on the respective determination output discriminated by the discrimination step possess a level control step of controlling the respective input levels of the pair of amplifiers,
In the level control step, the level of the balanced output data is set so as to attenuate the input level to the amplifier connected to the resistor determined that the level difference has exceeded the predetermined set value by the determination step by a predetermined value. When it is determined that the level difference between both ends of the resistor determined to exceed the predetermined set value has returned to the predetermined set value or less by the determining step, the input level to the amplifier is adjusted to a normal balanced level. A balanced output method for controlling the level of the balanced output data so as to return to the level at the time of output. In the level control step, it is determined that the level difference is equal to or less than the predetermined set value by the determining step for one resistance that is determined by the determining step to have exceeded the predetermined set value. has been controlled balanced output method according to claim 4, wherein you so that the input level of the other amplifier connected to the resistance is increased by a predetermined value. 5. The balanced output method according to claim 4, wherein in the determination step, a level difference based on a maximum value or an effective value of a level at a fixed time at both ends of the resistor is compared with the predetermined set value.

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