Abstract:
An operation apparatus is designed for use with a system to deal with operation information of the system. In the operation apparatus, an operation piece is manually operable to move in a linear or circular direction to a position indicative of the operation information. A detection section detects the position of the operation piece and outputs position data corresponding to the detected position. A drive section responds to position data inputted from the system to automatically move the operation piece to a position corresponding to the inputted position data. An acquiring section provisionally acquires a plurality of reference position data which are outputted from the detection section when the operation piece is placed at a plurality of reference positions such that the respective reference position data correspond to the respective reference positions. A correcting section corrects the position data outputted from the detection section according to the provisionally acquired reference position data and outputs the corrected position data to the system.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field of the Invention 
   The present invention relates to a fader position detection apparatus and a fader position control apparatus. More specifically, the present invention relates to a technology capable of accurately acquiring position data and moving a sliding piece of the fader to a target position despite a variance of accuracy of the electric fader&#39;s variable resistor and despite a variance of mounting positions of the faders on an operation panel. 
   2. Prior Art 
   Conventionally, an audio system such as a digital mixer often uses an operation panel containing an electric fader to set various parameter values (e.g., see patent document 1). The electric fader has a variable resistor that moves in interlock with a sliding piece. When the sliding piece is manually operated, its operated position is detected as a voltage value or a current value that varies with a resistance value of the variable resistor. An A/D converter converts the voltage value or current value into a digital value. The converted value is supplied as position data to a system CPU that controls the digital mixer. The CPU converts the supplied position data into an attenuation factor and saves it in a current memory. The CPU then supplies the attenuation factor to a DSP (digital signal processor) in a signal processing section of the digital mixer. During the mixing process of audio signals, the DSP controls attenuation factors of each channel corresponding to each fader in accordance with the supplied attenuation factor value. 
   The electric fader has a motor drive section for setting the sliding piece to a specified position. For example, the digital mixer stores setting data as a scene for mixing audio signals including each attenuation factor of each channel. Some digital mixers have a function of recalling (invoking) the scene to resume the specified state of mixing. When the scene is recalled, the CPU reads the setting data (including the attenuation factors) for the scene, and copies it to the current memory. The sliding piece of the corresponding fader is electrically moved to a specified position so that the sliding piece position matches a position corresponding to the attenuation factor value. The same applies to the auto-mix function that automates all mixing operations. When a fader moving event is reproduced at a specified timing according to the time stamp during auto-mix reproduction, the fader&#39;s sliding piece is electrically moved to a position corresponding to the attenuation factor specified by that event. 
   The electric fader is provided with a mechanism to turn off the electrical driving when a user manually commences operation of the fader&#39;s sliding piece while it is driven electrically. 
   The above mentioned Patent document 1 is Japanese Patent Publication No. 2684808 
   The conventional electric fader is subject to a variance of variable resistor accuracies and, therefore, subject to a variance of operation positions to be detected. Since resistance changes are uneven depending on positions of the fader&#39;s variable resistor, for example, this may degrade the linearity of detected fader positions. The fader is provided with a scale of graduations such as 0 dB and −10 dB to indicate the current position of the sliding piece. Positioning the sliding piece to a particular graduation does not necessarily provide an accurate attenuation factor indicated by the graduation, since there is always a mechanical error. 
   Further, it is possible to provide a plurality of faders with the same attenuation factor and electrically drive the sliding pieces so as to be moved to the position corresponding to the same attenuation factor. In this manner, the sliding pieces of the faders should all align to the same position horizontally. However, there have been cases where the sliding pieces of the faders are misaligned due to variable resistor errors of the faders. On the other hand, even if sliding pieces of the adjacent faders are manually adjusted to the same position, the faders do not necessarily generate the same attenuation factor due to possible errors. 
   When the operation panel of the digital mixer system is repaired to replace a faulty fader, a replaced new fader must conform to the characteristics of the other faders. Otherwise, the above-mentioned problems occur. Further, the replacement fader must be precisely aligned to the mounting position. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in consideration of the foregoing. It is therefore an object of the present invention to acquire accurate position data corresponding to displayed scale of graduations and electrically move a sliding piece of the fader to a precise target position corresponding to the displayed graduations despite variances of electric fader accuracies and mounting positions. It is another object of the present invention to eliminate the need for selecting a suitable fader conforming to characteristics of the other faders during replacement and the need for precisely aligning a fader to the mounting position. 
   In order to achieve the above object, an inventive operation apparatus is designed for use with a system to deal with operation information of the system. The inventive operation apparatus comprises an operation piece manually operable to move in a linear or circular direction to a position indicative of the operation information, a detection section that detects the position of the operation piece and outputs position data corresponding to the detected position, an acquiring section that provisionally acquires a plurality of reference position data which are outputted from the detection section when the operation piece is placed at a plurality of reference positions such that the respective reference position data correspond to the respective reference positions, and a correcting section that corrects the position data outputted from the detection section according to the provisionally acquired reference position data and outputs the corrected position data to the system. 
   In a specific form, the operation apparatus for use with a system to deal with operation information of the system, comprises an operation piece manually operable to move in a linear or circular direction to a position indicative of the operation information, a detection section that detects the position of the operation piece and outputs position data PD corresponding to the detected position, a first acquiring section that provisionally acquires first reference position data a i  which is outputted from the detection section when the operation piece is placed at a first reference position, and that provisionally acquires second reference position data a i+1  which is outputted from the detection section when the operation piece is placed at a second reference position, a second acquiring section that acquires first correct position data b i  which is predetermined in correspondence to the first reference position and acquires second correct position data b i+1  which is predetermined in correspondence to the second reference position, and that calculates a coefficient C i  according to the following first equation C i =(b i+1 −b i )/(a i+1 −a i ), and a correcting section that operates when the position data PD falls between the first reference position data a i  and the second reference position data a i+1  for correcting the position data PD outputted from the detection section according to the following second equation and outputting the corrected position data CPD to the system, where the second equation is CPD=b i +C i ×(PD−a i ). 
   In another aspect, an inventive operation apparatus for use with a system to deal with operation information of the system, comprises an operation piece manually operable to move in a linear or circular direction to a position indicative of the operation information, a detection section that detects the position of the operation piece and outputs position data corresponding to the detected position, a drive section responsive to target position data inputted from the system to automatically move the operation piece to a target position corresponding to the inputted target position data, an acquiring section that provisionally acquires a plurality of reference position data which are outputted from the detection section when the operation piece is placed at a plurality of reference positions such that the respective reference position data correspond to the respective reference positions, and a converting section that converts the target position data inputted from the system according to the respective reference position data, and outputs the converted target position data effective to enable the drive section to accurately place the operation piece at the target position. 
   In a specific form, the inventive operation apparatus for use with a system to deal with operation information of the system, comprises an operation piece manually operable to move in a linear or circular direction to a position indicative of the operation information, a detection section that detects the position of the operation piece and outputs position data corresponding to the detected position, a drive section responsive to target position data TPD inputted from the system to automatically move the operation piece to a target position corresponding to the inputted target position data TPD, a first acquiring section that provisionally acquires first reference position data a j  which is outputted from the detection section when the operation piece is placed at a first reference position, and that provisionally acquires second reference position data a j+1  which is outputted from the detection section when the operation piece is placed at a second reference position, a second acquiring section that acquires first correct position data b j  which is predetermined in correspondence to the first reference position and acquires second correct position data b j+1  which is predetermined in correspondence to the second reference position, and that calculates a coefficient D j  according to the following first equation D j =(a j+1 −a j )/(b j+1 −b j ), and a converting section that operates when the target position data TPD falls between the first correct position data b j  and the second correct position data b j+1  for converting the target position data TPD according to the following second equation and outputting the converted target position data XPD effective to enable the drive section to accurately place the operation piece at the target position, where the second equation is presented by XPD=a j +D j ×(TPD−b j ). 
   Preferably, the inventive operation apparatus further comprises a control section that controls the drive section to stop the operation piece when the detected position data outputted from the detection section coincides with the converted target position data XPD. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an electric fader according to an embodiment of the present invention. 
       FIG. 2  is a block diagram of a digital mixer according to the embodiment. 
       FIGS. 3(   a ) through  3 ( c ) show flowcharts of routines for obtaining position data from faders and correcting the obtained position data. 
       FIGS. 4(   a ) and  4 ( b ) show flowcharts of routines for driving faders. 
       FIG. 5  shows the relationship among a fader&#39;s sliding piece position, detected position data, and corrected position data. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will be described in further detail with reference to the accompanying drawings. 
     FIG. 1  shows a block configuration of an electric fader according to an embodiment of the present invention. The fader may be mounted in an operating panel of a system such as digital audio mixer for dealing with operation information of the audio mixer system. The electric fader comprises a motor control section  101 , a drive section  102 , a fader section  103  having a motor-driven sliding piece  104 , and a position detection section  105 . The position detection section  105  includes an analog/digital (A/D) converter and is designed to be capable of A/D conversion in an entire range in which fader sliding pieces can move. When the sliding piece  104  of the fader section  103  is operated manually, the position detection section  105  detects a voltage value or a current value that changes linearly in accordance with positions of the sliding piece  104 . The position detection section  105  uses the A/D converter to convert the voltage value or the current value into a digital value and outputs this value as position data. In this specification, a term “position linear data” is used to represent data that linearly varies on the scale of positions or angles of rotation (millimeters or radians) for operation devices. In addition, a term “decibel linear data” is used to represent data such as sound volume data that linearly varies on the decibel scale. In this specification, data termed “position data” in any combination is all position linear data. All the “attenuation factor data” signifies decibel linear data. 
   When an instruction from the CPU is used to move the sliding piece  104  to a specified position, the CPU supplies the motor control section  101  with converted position data (digital value) and a drive-on signal. The motor control section  101  generates a voltage value or a current value corresponding to the supplied converted position data, drives the sliding piece  104  using a motor, and moves the sliding piece  104  to a position corresponding to the converted position data. When the sliding piece  104  is moved, the position detection section  105  outputs position data corresponding to the position. The motor control section  101  moves the sliding piece  104  until position data from the position detection section  105  equals the converted position data. In this manner, the sliding piece  104  is aligned to the position corresponding to the converted position data. 
   As already mentioned in the prior art and the problems to be solved by the invention, the variable resistor of the fader section  103  is subject to variances of accuracy. Resistance changes are not always uniform with respect to sliding piece positions. There are also errors in the mounting position for the variable resistor of the fader section  103 . Accordingly, the above-mentioned problems occur if the electric fader shown in  FIG. 1  is used as is for a digital mixer. To avoid this, the present invention corrects position data output from the electric fader in  FIG. 1  to an accurate value for use. A target position for the sliding piece is corrected and supplied as converted position data. 
   The principle of the present invention will now be described with reference to  FIG. 5 . The reference numeral  501  shows a state of actually mounting the fader section  103 . There is provided a 100 mm movable range for the fader&#39;s sliding piece. A range of approximately 1 mm at the top and the bottom of the movable range is not used for compensating a mounting error. A mechanical means may be provided to prevent the sliding piece from entering the range of approximately 1 mm at the top and the bottom. The range where the sliding piece can be positioned is marked with graduations such as ∞ dB, . . . , −20 dB, . . . , 0 dB, . . . , +10 dB. 
   A graph on the left of  FIG. 5  shows the relationship between position data PD and corrected position data CPD observed when the fader is manually operated to input operation information to the system, and shows the relationship between converted position data XPD and target position data TPD) observed when the fader is mechanically operated to input operation information from the system. The corrected position data CPD indicates accurate position data values the system CPU should receive as operation information in correspondence with the sliding piece&#39;s movable range marked with a scale of graduations −∞ dB through +10 dB. When the sliding pieces of all faders are positioned to −∞ dB despite various variances and errors, the CPU needs to receive b 1 , i.e., the corresponding accurate value as position data. Likewise, the CPU needs to receive b 2 , b 3 , and b 4  when the sliding piece is positioned to −20 dB, 0 dB, and +10 dB, respectively. The position data PD indicates actual position data that is actually output from the electric fader as configured in  FIG. 1 . The position data contains a displacement due to various variances and errors. That is to say, adjusting the sliding pieces to the same position on different faders does not always output the same position data value. 
   According to the embodiment, a plurality of reference positions is provided beforehand in the movable range from −∞ dB to +10 dB for the fader&#39;s sliding piece. When the sliding piece is adjusted to the reference positions before the use of the fader, reference position data is output. A coefficient needs to be determined for an arithmetic equation that keeps correspondence between the obtained position data and the above-mentioned corrected position data. When the fader is used, the arithmetic equation is used to find the corrected position data from the output position data. 
   Specifically, four reference positions −∞ dB, +20 dB, 0 dB, and +10 dB are specified in the sliding piece&#39;s movable range from −∞ dB to +10 dB. When the sliding piece is adjusted to these positions before the use of the fader, reference position data is output. It is assumed that the reference position data is output as al for −∞ dB, a 2  for −20 db, a 3  for 0 dB, and a 4  for +10 dB. It should be noted that values for al through a 4  vary with the respective faders due to various variances and errors of the faders. The reference position data obtained in this manner corresponds to position data PD indicated as al through a 4  in  FIG. 5 . 
   An arithmetic equation coefficient needs to be found so that correct position data b 1 , b 2 , b 3 , and b 4  can be obtained when the position data PD is a 1 , a 2 , a 3 , and a 4 , respectively, and so that an interval between the values can be interpolated according to the graph shown in  FIG. 5 . Specifically, it is necessary to find coefficient C i  of the following Equation 1 for range A i (i=1, 2, and 3) in FIG.  5 .
 
Coefficient  C   i =( b   i+1   −b   i )/( a   i+1   −a   i )  (Equation 1)
 
   When the fader is used, the following Equation 2 is used to find the corrected position data CPD depending on which range A i  contains the position data PD output from the electric fader in FIG.  1 .
 
 CPD=b   i   +C   i ×( PD−a   i )  (Equation 2)
 
   In this manner, the corrected position data is obtained by correcting the position data detected from the position detection section  105 . The final mixing process requires an attenuation factor, not a position. The obtained corrected position data CPD is converted into attenuation factor data AD and is stored in the current memory. That is to say, the attenuation factor data AD is converted into a value equivalent to attenuation factors −∞ dB (minimum value min), −20 dB, 0 dB, and +10 dB when the corrected position data CPD is b 1 , b 2 , b 3 , and b 4 , respectively. The mixer CPU supplies the DSP with the attenuation factor data AD obtained in this manner for executing various mixing processes. Generally, an error is contained in the least significant bit of the fader position data. Accordingly, the resolution (the number of bits) of the corrected position data needs to be less than or equal to that of the original position data. The attenuation factor data AD uses more bits than the corrected position data so as to provide a higher resolution than the corrected position data for fine graduations (−5 dB to +5 dB) on the fader. This is because the fader&#39;s position resolution can be maximized. 
   When the system CPU electrically drives the sliding piece to move to a target position corresponding to an intended attenuation factor, it just needs to perform an operation reverse to the above-mentioned correction of the position data. At the time When finding coefficient C i  in the above-mentioned Equation 1, it is also necessary to find coefficient D j  in the following Equation 3 for each range B j (j=1, 2, and 3) at the same time.
 
Coefficient  D   j =( a   j+1   −a   j )/( b   j+1   −b   j )  (Equation 3)
 
   When a targeted attenuation factor data is supplied to a control section of the fader, the CPU first converts the target attenuation factor data into target position data TPD that indicates a target position as a movement destination. The following Equation 4 is used to find converted position data XPD depending on the range B j  containing the target position data TPD.
 
 XPD=a   j   +D   j ×( TPD−b   j )  (Equation 4)
 
   When the motor control section  101  in  FIG. 1  is supplied with the resultant converted position data XPD and the drive-on signal, the sliding piece is moved to a proper position corresponding to the attenuation factor. 
     FIG. 2  shows a block configuration of the digital mixer system that detects and controls positions of the faders based on the principle as described in  FIG. 5 . The digital mixer system comprises a central processing unit (CPU)  201 , flash memory  202 , RAM (random access memory)  203 , a display  204 , an electric fader  205 , an operation device  206 , a waveform I/O interface  207 , a signal processing section (DSP)  208 , a miscellaneous I/O interface  209 , and a system bus  210 . 
   The CPU  201  is a processor to control the entire operation of the mixer. The flash memory  202  is nonvolatile memory that stores various programs executed by the CPU  201  and various data used by the CPU  201 . The RAM  203  is volatile memory used as a load area or a work area for programs executed by the CPU  201 . The display  204  displays various information provided on an external panel of the mixer. The electric fader  205  is a kind of an operation device for setting various parameters provided on an operation panel and has the configuration as shown in  FIG. 1 . The other operation device  206  is provided on the operation panel and is also operated by a user. The waveform I/O  207  is an interface with external devices for exchanging waveform signals. The DSP  208  executes various microprograms based on instructions from the CPU  201  to mix waveform signals input via the waveform I/O  207 , provide effects, and control sound volume levels. The DSP  208  outputs the processed waveform signal via the waveform I/O  207 . The miscellaneous I/O  209  is an interface for connecting the other devices. 
     FIG. 3  shows flowcharts of routines that are executed by the mixer&#39;s CPU  201  in  FIG. 2  to obtain and correct position data for the sliding piece  104  of the fader  103 . 
     FIG. 3(   a ) is an reference position data measuring flowchart to be performed as preprocessing for using the fader. This process is performed for calibration of the mounted faders according to job instructions after a mixer is assembled at the factory or after a mixer is repaired at the service center, for example. At step  301 , the display  204  or the communication I/O  209  is used to issue an instruction to a person or an external calibration device for adjusting the fader to −∞ dB. When the sliding piece  104  of the fader  103  is moved to the graduation position for attenuation factor −∞ dB by means of a person&#39;s hand, a calibration device&#39;s arm, or the like in accordance with the instruction, the corresponding reference position data al ( FIG. 5)  is measured. Likewise, at steps  302 ,  303 , and  304 , the sliding piece  104  is moved to the graduation positions for attenuation factors −20 dB, −0 dB, and +10 dB to measure the corresponding reference position data a 2 , a 3 , and a 4 . At step  305 , as shown in  FIG. 5 , the above-mentioned (Equation 1) is used to find coefficient data C i  for correction corresponding to range A i (i=1, 2, and 3). Also at step  305 , as shown in  FIG. 5 , the above-mentioned (Equation 3) is used to find coefficient D i  corresponding to range B j (j=1, 2, and 3). 
     FIG. 3(   b ) is a fader processing flowchart that is periodically performed for each fader. At step  311 , position data PD is retrieved from the position detection section  105  corresponding to the fader. At step  312 , it is determined whether or not the position data PD is changed. It is assumed that a value of the previous position data PD is stored. When no change is found, the process terminates. When a change is found, the current position data PD is converted into corrected position data CPD at step  313 . The above-mentioned (Equation 1) is used for this conversion depending on which range A i  contains the position data PD. At step  314 , the corrected position data CPD is converted into attenuation factor data AD. At step  315 , the attenuation factor for the fader in the current memory is changed to the found attenuation factor data AD. 
     FIG. 3(   c ) is a flowchart showing a current process that is performed periodically. At step  321 , each data in the current memory is checked. At step  322 , it is determined whether or not data in the current memory is changed. It is assumed that each value of the previous current memory is stored. When no change is found, the process terminates. Where a change is found, the DSP  208  is controlled for its mixing process depending on a value of the changed data at step  323 . When a fader is operated to change the attenuation factor, for example, the current memory will store, as its attenuation factor, the attenuation factor for a musical sound signal on a channel corresponding to the fader. At step  324 , the display  204  is controlled so as to display the change. The process then terminates. 
     FIG. 4  shows flowcharts of processes executed by the CPU  201  for moving the sliding piece  104  of the fader  103  to a specified position. 
     FIG. 4(   a ) shows a process of issuing a fader event from the auto-mix function, for example. The auto-mix function provides fully automatic mixing operations. First, the auto-mix function issues a recording instruction to give time stamps to events indicating the contents of operations that are sequentially performed in accordance with the mixer. The time stamp indicates the timing of each event. A sequence of events provided with time stamps is recorded as auto-mix data. Thereafter, the auto-mix function issues a reproduction instruction to reproduce the operations sequentially performed in accordance with the mixer based on the recorded auto-mix data. During the auto-mix reproduction, each event is issued at the timing indicated by the time stamp given to the event contained in the auto-mix data. A fader event is one of events recorded by the auto-mix function and indicates an attenuation factor corresponding to the position to which the fader is moved during auto-mix recording. When the fader event is issued during auto-mix reproduction, the attenuation factor indicated by the fader event is assumed to be the target attenuation factor. The fader&#39;s sliding piece is automatically moved to the position of the target attenuation factor. The fader process in  FIG. 3(   b ) converts the position of the fader&#39;s moved sliding piece into attenuation factor data which is then written to the current memory. The current process in  FIG. 3(   c ) provides a mixing process with the attenuation factor data written to the current memory. 
   At step  401 , the fader event process defines a target attenuation factor to be TAD. At step  402 , the process converts the target attenuation factor TAD into target position data TPD. At step  403 , the process converts the target position data TPD into converted position data XPD. The above-mentioned (Equation 4) is used for this conversion depending on which range B i  contains the target position data TPD. At step  404 , the process transmits the converted data XPD and the drive-on signal to the motor control section  101 , and then terminates. At step  401  above, it may be preferable to directly (without intermediation of the fader process in  FIG. 3(   b )) write the attenuation factor data indicated by the fader event to the current memory. 
     FIG. 4(   b ) is a flowchart showing a scene recall event process that is performed when an operator selects one of scenes stored in the scene memory and performs a scene recall operation. When each scene is stored, data in the current memory indicates mixing setup states of the mixer. The scene memory records a plurality of scenes that are snapshots of the data in the current memory. At step  411 , the process copies data for a scene to be recalled to the current memory. The current process in  FIG. 3(   c ) above provides the mixing process with the data written to the current memory. At step  412 , the process checks each attenuation factor in the current memory. When a change is found at step  413 , the process advances to step  414 . The process uses the changed attenuation factor as a target attenuation factor to generate a fader event, and then terminates. When no change is found at step  413 , the process terminates. 
   As mentioned above, when mixers are manufactured in a factory, for example, it is necessary to measure reference position data for all faders as shown in  FIG. 3(   a ) and find and store coefficients C i  and D j . In this case, it is a good practice to use a tool for aligning a plurality of faders to a target reference position at a time and concurrently measure reference position data and compute coefficients rather than aligning sliding pieces of individual faders to the reference position for measurement by means of human hands or machine arms. For this purpose, it may be preferable to provide part of the mixer panel with a projection or a dent for alignment of the tool. 
   When a mixer is repaired, one or several faders are replaced. To measure reference position data in this case, it may be preferable to electrically move sliding pieces of all faders to the reference positions, manually adjust misaligned sliding pieces to the reference positions, and then detect reference position data of the replaced fader with this state. In this manner, it is possible to confirm reference positions of the other faders and manually move the replaced fader to the reference position. Further, it may be also preferable to be able to adjust reference positions of the unreplaced faders. 
   While the above-mentioned embodiment uses the variable resistor to detect fader positions, the present invention may be applied to the other elements such as a rotary encoder to detect fader positions. 
   The A/D converter in the position detection section is designed to be able to A/D convert the entire movable range of faders and ensure a margin of 1 mm. This margin is not limited to 1 mm, i.e., 1% of the movable range 100, but may be changed to approximately 0.2% to 2% depending on the fader performance and the like. 
   The present invention corrects data values detected from faders at the stage of position-linear position data, not after converting position data into decibel-linear attenuation factor data. This makes the correction process efficient and simple and improves the mixer response. If the accuracy is unchanged, the index data for correction needs the smaller number of bits than that for the correction at the decibel-linear stage. 
   While the above-mentioned embodiment calculates coefficient C or D for correction before measuring reference position data, it may be preferable to calculate the coefficient at any point until position data is corrected. However, calculating the coefficient beforehand saves the time for the correction process, making it advantageous to the response. It is also possible to arithmetically modify the equations Equation 1 through Equation 4 for substantially the same calculation. In this case, a coefficient in the modified equation may differ from that described in the above-mentioned embodiment. 
   The above-mentioned embodiment corrects position data for the fader using characteristics of the linear interpolation between four measurement points as shown in  FIG. 5 . Further, it may be preferable to correct the position data using characteristics of curve interpolations such as the Lagrangian interpolation and the spline interpolation instead of the linear interpolation. In such case, coefficients used for the correction calculations depend on the respective calculation systems. When the spline interpolation is used, for example, the 3D spline interpolation can be used to find an equation for a curve crossing the four points in  FIG. 5 . This equation can be used for conversion from position data into corrected position data or conversion from target position data into converted position data. 
   While the above-mentioned embodiment corrects position data for the faders based on values of the four measurement points, the correction may use a plurality of measurement points more or fewer than four. For example, it is possible to use three points −∞ dB, 0 dB, and +10 dB or five points −∞ dB, −30 dB, −10 dB, 0 dB, and +10 dB. 
   As mentioned above, the present invention provisionally obtains reference position data that can be generated by aligning the sliding piece of an operation device such as the fader to a specified reference position. When the operation device is actually used, actual position data is corrected based on the reference position data and is output as corrected position data. Therefore, it is possible to acquire accurate corrected position data corresponding to scale graduations of the operation devices despite variances of accuracies and mounting positions. 
   There is provided target position data to indicate a target position to which the sliding piece should be moved. This target position data is converted based on the reference position data to generate converted position data. The converted position data is supplied to the drive section of the operation device to drive it. In this manner, the operation device&#39;s sliding piece can be electrically moved to the accurate target position corresponding to the graduation. When replacing operation devices, it is unnecessary to select a suitable operation device conforming to characteristics of the other operation devices or to precisely align an operation device to the mounting position.