JP2019165386A - Signal analysis method and signal analysis device - Google Patents

Abstract

To precisely identify temporal correspondence between signals.SOLUTION: A signal processing unit 21 applies signal processing to reduce a difference between signal values to an acoustic signal A1. An analysis processing unit 22 identifies temporal correspondence between the acoustic signal A1 and an acoustic signal A2 by comparing an acoustic signal B1 after the signal processing with an acoustic signal B2.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a technique for analyzing temporal correspondence between a plurality of signals.

  Techniques for analyzing temporal correspondence between a plurality of signals have been conventionally proposed. For example, Patent Document 1 discloses a technique for analyzing a time difference between a plurality of pieces of speech encoded information by comparing signal value patterns. The plurality of pieces of speech encoded information are compared with each other after components whose signal values are outside a predetermined range are extracted.

JP 2009-10548 A

  In the technique of Patent Document 1, components having large amplitudes are compared among the pieces of speech encoded information. However, the amplitude of components that are important in analyzing temporal correspondence between signals may be relatively small. Therefore, in the configuration in which components having large amplitudes are compared as in the technique of Patent Document 1, there is a problem that the temporal correspondence between signals cannot be specified with high accuracy. In view of the above circumstances, an object of the present invention is to specify the temporal correspondence between signals with high accuracy.

  In order to solve the above problems, an information processing method according to a preferred aspect of the present invention performs signal processing for reducing a difference in signal values on a first signal, and performs first processing after the signal processing is performed. The temporal correspondence between the first signal and the second signal is specified by comparing the signal with the second signal.

  An information processing apparatus according to a preferred aspect of the present invention includes: a signal processing unit that performs signal processing for reducing a difference in signal values for a first signal; a first signal after execution of the signal processing; An analysis processing unit that identifies a temporal correspondence between the first signal and the second signal by comparing the signal is provided.

It is a block diagram which illustrates the composition of the information processor concerning an embodiment of the present invention. It is explanatory drawing of the temporal relationship of two lines of acoustic signals. It is explanatory drawing of the content after a synthesis | combination. It is a block diagram which illustrates the functional composition of an information processor. It is explanatory drawing of signal processing. It is a flowchart which illustrates the specific procedure of operation | movement of information processing apparatus.

  FIG. 1 is a block diagram illustrating the configuration of an information processing apparatus 100 according to a preferred aspect of the present invention. The information processing apparatus 100 (an example of a signal analysis apparatus) is a computer system that reproduces various contents including video and sound. As illustrated in FIG. 1, the information processing apparatus 100 includes a control device 11, a storage device 12, and a playback device 13. For example, various information terminals such as a mobile phone, a smartphone, a tablet terminal, or a personal computer are preferably used as the information processing apparatus 100.

  The control device 11 is a processing circuit such as a CPU (Central Processing Unit), for example, and comprehensively controls each element of the information processing device 100. The control device 11 includes one or more processing circuits. The storage device 12 is a memory that stores a program executed by the control device 11 and various data used by the control device 11. For example, a known recording medium such as a magnetic recording medium or a semiconductor recording medium, or a combination of a plurality of types of recording media is suitable as the storage device 12. Note that a storage device 12 (for example, a cloud storage) separate from the information processing device 100 may be prepared, and the control device 11 may execute writing and reading with respect to the storage device 12 via a communication network. That is, the storage device 12 may be omitted from the information processing device 100.

  The storage device 12 stores content X1 and content X2. The content X1 and the content X2 are, for example, video works that record a common subject at different positions and angles of view in the acoustic space. For example, content X1 and content X2 received from another device via the communication network are stored in the storage device 12. Note that the information processing apparatus 100 may receive the content X1 and the content X2 recorded by the recording device including the imaging device and the sound collection device.

  The content X1 is expressed by the video signal V1 and the audio signal A1, and the content X2 is expressed by the video signal V2 and the audio signal A2. Each video signal Vn (n = 1, 2) is a signal representing a moving image captured by the imaging device, and each acoustic signal An is a signal representing an acoustic waveform collected by the sound collection device. Specifically, the acoustic signal An is represented by a time series of signal values representing the sound pressure level (intensity). The format of the video signal Vn and the audio signal An is arbitrary. The period in which the recording is performed overlaps between the content X1 and the content X2. Therefore, as illustrated in FIG. 2, the acoustic signal A1 and the acoustic signal A2 include a common acoustic component. However, since the recording start time differs between the content X1 and the content X2, the phase differs between the acoustic signal A1 and the acoustic signal A2.

  As illustrated in FIG. 1, the control device 11 generates the content Y by combining the content X1 and the content X2. The content Y is expressed by a video signal Vy and an audio signal Ay. As illustrated in FIG. 3, the video signal Vy is an image in which an image represented by the video signal V1 of the content X1 and an image represented by the video signal V2 of the content X2 are juxtaposed. The acoustic signal Ay is generated by mixing the acoustic signal A1 and the acoustic signal A2. Note that one of the acoustic signal A1 and the acoustic signal A2 may be used as the acoustic signal Ay.

  The playback device 13 plays back the content Y generated by the control device 11. Specifically, the playback device 13 includes a display device 131 and a sound emitting device 132. The display device 131 is configured by a liquid crystal display panel, for example, and displays an image represented by the video signal Vy of the content Y. The sound emitting device 132 is, for example, a speaker or a headphone, and emits sound represented by the sound signal Ay of the content Y.

  FIG. 4 is a block diagram illustrating a functional configuration of the information processing apparatus 100. As illustrated in FIG. 4, the control device 11 executes a program stored in the storage device 12 to generate a plurality of functions (a signal analysis unit 20, a content analysis unit 20, a content Y from the content X 1 and the content X 2. A synthesis processing unit 30 and a reproduction control unit 40) are realized. Note that the function of the control device 11 may be realized by a set (that is, a system) of a plurality of devices configured separately from each other, or part or all of the function of the control device 11 is realized by a dedicated electronic circuit. May be.

  The signal analysis unit 20 analyzes the temporal correspondence between the acoustic signal A1 (example of the first signal) and the acoustic signal A2 (example of the second signal). Specifically, the time difference T between the acoustic signal A1 and the acoustic signal A2 is specified. As illustrated in FIG. 2, the time difference T is the time when a specific sound is generated in the sound signal A 1 when the sound signal A 1 and the sound signal A 2 are arranged so that the start points are common on the time axis. This is the time difference (ie, phase difference) from the point in time when the sound is produced in the sound signal A2. The difference between the start time of recording of the acoustic signal A1 and the start time of recording of the acoustic signal A2 may be expressed as a time difference T.

  The composition processing unit 30 in FIG. 4 synthesizes the content X1 and the content X2 in a state where they are synchronized with each other. Content Y is generated by combining the content X1 and the content X2 by the composition processing unit 30. The synchronization between the content X1 and the content X2 means a state in which a specific sound or image is reproduced at the same time on the time axis for the content X1 and the content X2. The composition processing unit 30 synchronizes the content X1 and the content X2 by moving one of the content X1 and the content X2 on the time axis with respect to the other by the time difference T analyzed by the signal analysis unit 20. Specifically, the synthesis processing unit 30 generates the video signal Vy of the content Y by synthesizing the video signal V1 and the video signal V2 in a state of being synchronized with each other. Further, the synthesis processing unit 30 generates the acoustic signal Ay of the content Y by synthesizing the acoustic signal A1 and the acoustic signal A2 in a state of being synchronized with each other. As illustrated in FIG. 3, a video work (that is, a multi-angle moving image) in which a common subject is recorded at different positions and angles of view is generated as the content Y. In the above-described configuration in which one of the acoustic signal A1 and the acoustic signal A2 is selected as the acoustic signal Ay, one of the acoustic signal A1 and the acoustic signal A2 synchronized with each other according to the analysis result by the signal analysis unit 20 is acoustic. Selected as signal Ay.

  The playback control unit 40 in FIG. 4 causes the playback device 13 to play back the content Y generated by the composition processing unit 30. That is, the playback control unit 40 supplies the video signal Vy to the display device 131 to display the image of the content Y on the display device 131, and supplies the sound signal Ay to the sound emitting device 132 to generate the sound of the content Y. The sound emitting device 132 emits sound.

  As illustrated in FIG. 4, the signal analysis unit 20 includes a signal processing unit 21 and an analysis processing unit 22. The signal processing unit 21 generates an acoustic signal B1 by signal processing on the acoustic signal A1, and generates an acoustic signal B2 by similar signal processing on the acoustic signal A2. The signal processing executed by the signal processing unit 21 is processing for reducing a difference in signal value in the acoustic signal An. The signal processing of this embodiment is a limiting process that limits the range of signal values of the acoustic signal An.

  FIG. 5 is an explanatory diagram of the restriction process. As illustrated in FIG. 5, the limiting process is a process (that is, a limiter) that limits the range of the signal value of the acoustic signal An to the range R. That is, the amplitude of the acoustic signal An is reduced to the range R by the limiting process. The upper limit value rH of the range R is lower than the maximum value that the signal value of the acoustic signal An can take, and the lower limit value rL of the range R is higher than the minimum value that the signal value of the acoustic signal An can take. The signal processing unit 21 changes the signal value exceeding the upper limit value rH in the acoustic signal An to the upper limit value rH (that is, clipping), and changes the signal value below the lower limit value rL to the lower limit value rL. That is, the portion outside the range R in the acoustic signal An is deleted. On the other hand, the signal value within the range R is not changed in the acoustic signal An. Therefore, as a result of the limiting process, the amplitude of the section of the acoustic signal An having a large amplitude is limited, and the section having a small amplitude is maintained. That is, the signal processing unit 21 emphasizes the acoustic signal An with a degree that differs depending on the signal value.

  As understood from the above description, the signal processing by the signal processing unit 21 is a process of emphasizing a component having a small amplitude relative to a component having a large amplitude in the acoustic signal An. That is, the signal processing unit 21 generates the acoustic signal B1 by emphasizing a component having a small amplitude in the acoustic signal A1, and generates the acoustic signal B2 by enhancing a component having a small amplitude in the acoustic signal A2.

  The range R in this embodiment is a positive / negative symmetrical range as understood from FIG. That is, the midpoint between the upper limit value rH and the lower limit value rL of the range R corresponds to zero of the signal value. It may be expressed that the absolute value matches between the upper limit value rH and the lower limit value rL. However, the range R may be a positive / negative asymmetric range.

  The analysis processing unit 22 in FIG. 4 compares the acoustic signal B1 after the execution of the signal processing described above with the acoustic signal B2 after the execution of the signal processing, so that the acoustic signal B1 and the acoustic signal B2 are compared. A temporal correspondence (ie, time difference T) is specified. Specifically, the analysis processing unit 22 calculates the time difference T by evaluating the similarity of the waveform between the acoustic signal B1 and the acoustic signal B2. A cross-correlation is suitable as an index of the similarity of the waveform between the acoustic signal B1 and the acoustic signal B2. That is, the analysis processing unit 22 sequentially calculates the cross-correlation while changing the time difference τ between the acoustic signal B1 and the acoustic signal B2, and when the cross-correlation becomes the maximum value (that is, when the similarity of waveforms is the maximum). The time difference τ between the acoustic signal B1 and the acoustic signal B2 is specified as the time difference T.

  FIG. 6 is a flowchart illustrating a specific procedure of a process in which the control device 11 generates the content Y. For example, the process in FIG. 6 is started in response to an instruction from the user. When the processing of FIG. 6 is started, the signal processing unit 21 generates an acoustic signal B1 by signal processing on the acoustic signal A1, and generates an acoustic signal B2 by signal processing on the acoustic signal A2 (S1). As described above, the signal processing includes a limiting process for reducing the amplitude of each acoustic signal An to the range R. The analysis processing unit 22 analyzes the time difference T between the two by comparing the acoustic signal B1 and the acoustic signal B2 after the signal processing (S2). The composition processing unit 30 synchronizes both the content X1 and the content X2 by moving the content X1 and the content X2 on the time axis by the time difference T analyzed by the analysis processing unit 22 (S3). The composition processing unit 30 generates the content Y by combining the content X1 and the content X2 that are in synchronization with each other (S4). The reproduction control unit 40 causes the reproduction device 13 to reproduce the content Y synthesized by the synthesis processing unit 30 (S5).

  As described above, in the present embodiment, signal processing for reducing the difference in signal value is performed on each acoustic signal An. According to the above configuration, compared to a configuration in which signal processing is not executed (hereinafter referred to as “comparative”), a portion having a relatively small signal value in each acoustic signal An is reflected in the comparison between the two. Therefore, as illustrated below, it is possible to specify the temporal correspondence between the acoustic signal A1 and the acoustic signal A2 with high accuracy.

  The proportionality is a configuration for calculating a cross-correlation between the acoustic signal A1 and the acoustic signal A2. In contrast, the portion of each acoustic signal An having a large amplitude contributes predominantly to the cross-correlation, and the portion of the acoustic signal An having a small amplitude contributes sufficiently. However, in order to synchronize the acoustic signal A1 and the acoustic signal A2, a portion having a small amplitude in each acoustic signal An may be important. For example, assume a scene in which a low volume conversation sound is continuously generated in an environment in which a high volume sound effect is generated periodically. In contrast, an effect sound having a large volume contributes predominantly to the cross-correlation, so that an error corresponding to an integral multiple of the sound effect generation period may occur in the time difference T. In contrast to the proportionality, in the embodiment, the degree to which the conversational sound contributes to the cross-correlation relatively increases. Therefore, it is possible to specify the time difference T with high accuracy in consideration of the conversational sound with a small volume. Is possible.

  In the present embodiment, there is also an advantage that the temporal correspondence between the acoustic signal A1 and the acoustic signal A2 can be specified with high accuracy by a simple restriction process for restricting the range of the signal value. In the configuration in which the signal value of each acoustic signal An is limited to a positive / negative asymmetric range R, the phase of the acoustic signal An may change before and after the signal processing. In the present embodiment, since the signal value is limited to a range R in which the signal value is symmetrical, the change in the phase of each acoustic signal An caused by the signal processing is suppressed. Therefore, the above-described effect that the temporal correspondence between the acoustic signal A1 and the acoustic signal A2 can be specified with high accuracy is particularly remarkable.

<Modification>
Examples of specific modifications added to the above-exemplified aspects are illustrated below. Two or more aspects arbitrarily selected from the following examples may be appropriately combined as long as they do not contradict each other.

(1) The specific content of the signal processing for reducing the difference in signal value of the acoustic signal An is not limited to the limiting processing exemplified in the above-described embodiment. For example, the signal processing unit 21 may execute signal processing for amplifying the sound signal An to such an extent that a clip is generated in each sound signal An. Further, for example, the amplitude of the acoustic signal An may be limited within the range R by deleting a part of the bit string representing the signal value of the acoustic signal An (that is, lowering the bit).

  By smoothing the acoustic signal An on the time axis, the difference in the signal value of the acoustic signal An can be reduced. For the smoothing of the acoustic signal An, for example, a process of calculating a time-series moving average or root mean square (RMS) of signal values is suitable. Moreover, you may employ | adopt as a signal process with respect to the acoustic signal An the compression process (compressor) which reduces the signal value exceeding a predetermined threshold value with the compression rate according to the said signal value. Differences in signal values may be reduced by signal processing that increases the sound rise time (attack time).

  The signal processing unit 21 may execute signal processing for extracting a time series of signal values within a predetermined range R among a plurality of signal values constituting the acoustic signal An. That is, signal values outside the range R are ignored. As described above, the signal processing for extracting the signal value within the range R is also included in the concept of the limiting processing, similarly to the signal processing of the above-described form for limiting the signal value within the range R.

  For each of a plurality of different (K) ranges R1 to RK, a restriction process using the range Rk (k = 1 to K) may be executed. That is, K-system acoustic signals Bn_1 to Bn_K corresponding to different ranges Rk are generated from each of the acoustic signal A1 and the acoustic signal A2. Each of the K ranges R1 to RK is, for example, a positive / negative symmetrical range, and the numerical value width is different for each range Rk. The analysis processing unit 22 calculates the cross correlation by comparing the acoustic signal B1_k generated from the acoustic signal A1 with the acoustic signal B2_k generated from the acoustic signal A2. That is, K cross-correlations corresponding to different ranges Rk are calculated. The analysis processing unit 22 analyzes, for example, the representative value (for example, the average value or the median value) of the time difference T specified from each of the K cross-correlations, and the analysis result of the temporal correspondence between the acoustic signal A1 and the acoustic signal A2. Confirm as

  As understood from the above examples, the signal processing executed by the signal processing unit 21 is comprehensively expressed as processing for reducing the difference in the signal value of the acoustic signal An, specifically, the amplitude of the acoustic signal An. Is a process of emphasizing a component with a small relative to a component with a large amplitude.

(2) In the above-described embodiment, the signal processing is performed on the acoustic signal An that represents the acoustic waveform (that is, the temporal change in the sound pressure level), but the signal (first signal or second signal) that is the target of signal processing. ) Is not limited to the above examples. For example, signal processing for reducing a difference in signal values may be executed on a signal representing a time series of feature values extracted from the sound of the content Xn. Examples of acoustic feature values include pitch (fundamental frequency) or MFCC (Mel-Frequency Cepstrum Coefficients). In addition, signal processing may be executed for components in a specific frequency band extracted from the acoustic signal An.

  Further, a signal to be subjected to signal processing is not limited to a signal related to the sound of each content Xn. For example, the temporal correspondence between the two lightness signals may be specified by performing signal processing on the lightness signal representing the time series of the lightness of the image. Further, for example, by performing signal processing on an intensity signal that represents a time series of radio wave reception intensity in wireless communication, the temporal correspondence between the two systems of intensity signals may be specified. As understood from the above examples, the present invention is applied to processing of an arbitrary signal expressed by a time series of signal values, and the specific meaning of the signal values is not questioned.

(3) In the above-described embodiment, the signal processing is performed for both the acoustic signal A1 and the acoustic signal A2, but the signal processing may be performed for only one of the acoustic signal A1 and the acoustic signal A2. However, according to the configuration in which the signal processing is executed for both the acoustic signal A1 and the acoustic signal A2, not only the portion where the signal value is relatively small in the acoustic signal A1, but also the portion where the signal value is relatively small in the acoustic signal A2. Can also be reflected in the comparison by the analysis processing unit 22. Therefore, the effect that the temporal correspondence between the acoustic signal A1 and the acoustic signal A2 can be specified with high accuracy is particularly remarkable.

(4) In the above embodiment, the temporal correspondence is specified between the two systems of the acoustic signal A1 and the acoustic signal A2, but the temporal correspondence may be specified between the three or more systems. For example, it is possible to analyze temporal correspondence for each combination of selecting two systems of signals from three or more systems by using the same method as that described above.

(5) In the above-described embodiment, the case where the subject is common between the content X1 and the content X2 is illustrated for convenience, but the subject may be different between the content X1 and the content X2. However, in order to specify the temporal correspondence between the content X1 and the content X2 by comparing the acoustic signal A1 and the acoustic signal A2, the acoustic signal A1 and the acoustic signal A2 are both similar or common to each other. Ingredients need to be included. For example, for the content X1 that records a situation in which the subject 1 dances in an environment where a specific music is played back and a content X2 that records a scene in which the subject 2 dances in an environment where the music is played back, the acoustic signal A1 And the acoustic signal A2 contain a common acoustic component. Therefore, it is possible to specify the temporal correspondence between the content X1 and the content X2.

(6) Although the case where each content Xn is expressed by the video signal Vn and the audio signal An is illustrated in the above-described form, one or both of the content X1 and the content X2 may be configured only by the audio signal An. . For example, the signal analysis unit 20 analyzes temporal correspondence between the acoustic signal A1 and the acoustic signal A2, and the synthesis processing unit 30 synthesizes the acoustic signal A1 and the acoustic signal A2 in a synchronized state. Thus, the content Y (sound signal Ay) is generated. Further, the video signal Vn of each content Xn may be replaced with another signal.

(7) The function of the information processing apparatus 100 may be realized by a server device that communicates with a terminal device such as a mobile phone or a smartphone. For example, the information processing apparatus 100 specifies a temporal correspondence (specifically, a time difference T) between the acoustic signal A1 and the acoustic signal A2 received from the terminal apparatus, and transmits the identification result to the terminal apparatus. That is, the information processing apparatus 100 includes the signal analysis unit 20, and the synthesis processing unit 30 and the reproduction control unit 40 are mounted on the terminal device. Note that the signal analysis unit 20 and the synthesis processing unit 30 may be mounted on the information processing apparatus 100, and the content Y generated by the synthesis processing unit 30 may be transmitted to the terminal device. As exemplified above, the synthesis processing unit 30 and the reproduction control unit 40 may be omitted from the information processing apparatus 100.

(8) The function of the information processing apparatus 100 according to the above-described embodiment is realized by cooperation between a computer (for example, the control apparatus 11) and a program. The program according to the above-described embodiment is provided in a form stored in a computer-readable recording medium and installed in the computer. The recording medium is, for example, a non-transitory recording medium, and an optical recording medium (optical disk) such as a CD-ROM is a good example, but a known arbitrary one such as a semiconductor recording medium or a magnetic recording medium Including a recording medium of the form. Note that the non-transitory recording medium includes any recording medium except for a transient propagation signal (transitory, propagating signal), and does not exclude a volatile recording medium. In addition, the program may be provided to the computer in the form of distribution via a communication network.

<Appendix>
For example, the following configuration is grasped from the above-exemplified form.

  In a signal analysis method according to a preferred aspect (first aspect) of the present invention, signal processing for reducing a difference in signal values is performed on the first signal, the first signal after the execution of the signal processing, By comparing two signals, the temporal correspondence between the first signal and the second signal is specified. In the above aspect, since the signal processing for reducing the difference in the signal value is executed for the first signal compared with the second signal, the first signal is compared with the configuration in which the difference in the signal value of the first signal is not reduced. A portion having a relatively small signal value in one signal is reflected in the comparison with the second signal. Therefore, it is possible to specify the temporal correspondence between the first signal and the second signal with high accuracy.

  In a preferred example (second aspect) of the first aspect, the signal processing is performed on the second signal, and the first signal after execution of the signal processing is compared with the second signal after execution of the signal processing. To do. In the above aspect, the signal processing for reducing the difference in signal value is executed for both the first signal and the second signal. Therefore, not only a portion having a relatively small signal value in the first signal but also a portion having a relatively small signal value in the second signal can be reflected in the comparison between the first signal and the second signal. is there.

  In a preferred example (third aspect) of the first aspect or the second aspect, the signal processing includes a restriction process for restricting a range of the signal value. According to the above aspect, it is possible to reduce the difference in signal values by a simple process that limits the range of signal values.

  In a preferred example of the third aspect (fourth aspect), the limiting process is a process of limiting the signal value to a range of positive and negative symmetry. In the above aspect, since the signal value is limited to a positive / negative symmetric range, a change in phase caused by signal processing can be suppressed. Therefore, there is an advantage that the temporal correspondence between the first signal and the second signal can be specified with high accuracy.

  A preferable aspect of the present invention is realized also as an information processing apparatus that executes the information processing method of each aspect exemplified above or a program that causes a computer to execute the information processing method of each aspect exemplified above.

DESCRIPTION OF SYMBOLS 100 ... Information processing apparatus, 11 ... Control apparatus, 12 ... Memory | storage device, 13 ... Playback apparatus, 131 ... Display apparatus, 132 ... Sound emission apparatus, 20 ... Signal analysis part, 21 ... Signal processing part, 22 ... Analysis processing part, 30 ... composite processing unit, 40 ... reproduction control unit, X1, X2, Y ... content, V1, V2 ... video signal, A1, A2, B1, B2 ... acoustic signal.

Claims (8)

Performing signal processing on the first signal to reduce the difference in signal values;
A signal analysis method realized by a computer that identifies a temporal correspondence between the first signal and the second signal by comparing the first signal after execution of the signal processing and the second signal. Performing the signal processing on the second signal;
The signal analysis method according to claim 1, wherein the first signal after execution of the signal processing is compared with the second signal after execution of the signal processing. The signal analysis method according to claim 1, wherein the signal processing includes a restriction process that restricts a range of the signal value. The signal analysis method according to claim 3, wherein the limiting process is a process of limiting the signal value to a range of positive and negative symmetry. A signal processing unit that performs signal processing on the first signal to reduce a difference in signal values;
A signal analysis apparatus comprising: an analysis processing unit that identifies a temporal correspondence between the first signal and the second signal by comparing the first signal after the execution of the signal processing and the second signal . The signal processing unit performs the signal processing on the first signal and the second signal,
The signal analysis device according to claim 5, wherein the analysis processing unit compares the first signal after execution of the signal processing with the second signal after execution of the signal processing. The signal analysis apparatus according to claim 5, wherein the signal processing includes a restriction process for restricting a range of the signal value. The signal analysis apparatus according to claim 7, wherein the restriction process is a process of restricting the signal value to a positive / negative symmetrical range.

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