JP6201722B2 - Multipath evaluation apparatus and multipath evaluation method - Google Patents

Description

  The present invention relates to a multipath evaluation apparatus and a multipath evaluation method for evaluating multipath noise.

  Conventionally, multipaths that occur during propagation of R / F signals are detected using audio signals (audio signals) obtained by detecting radio wave signals (R / F signals) that have propagated through space. The technology to do is known. For example, Patent Document 1 describes a receiver used for an in-vehicle radio receiver or the like. In this receiver, the occurrence of multipath is detected based on at least one of an audio signal and a received signal level. Patent Document 2 describes a receiver including an integration circuit that detects a multipath by integrating a control signal having a predetermined pulse width in order to ensure detection of multipath noise.

JP-A-8-79109 JP 63-164632 A

  By the way, for example, in order to evaluate the performance of a part that suppresses multipath noise in a device (such as a radio tuner) that detects an R / F signal, the multi-signal included in the audio signal obtained from the R / F signal is used. A path noise evaluation index is required. When multipath is detected using the conventional technique, the total time of the multipath generation period in the evaluation target period of the time series data of the audio signal can be considered as such an evaluation index. However, when multipath noise is evaluated using the total time of the multipath generation period, the evaluation result is the result of human sensuously evaluating the sound of multipath noise (hereinafter referred to as “sensory evaluation result”). May be different). In other words, if the multi-pass generation period is long, the sensory evaluation result score should be worse, but if the sensory evaluation result score is good, or if the multi-pass generation period is short, the sensory evaluation result score Although it should improve, the score of the sensory evaluation result may deteriorate.

  It is an object of the present invention to suppress the difference between the evaluation result of multipath noise by the multipath evaluation apparatus and the sensory evaluation result.

  The present invention is a multipath evaluation apparatus for evaluating multipath noise included in an audio signal, and a multipath generation period in which a multipath has occurred is identified from an evaluation target period of time-series data of the audio signal. Based on the path period identification unit, the total time of the multipath generation period in the evaluation target period, and the time change rate of the power of the predetermined high frequency component of the audio signal in the multipath generation period, the multipath noise evaluation index is output And an index output unit.

  Further, in the present invention, the index output unit may output an evaluation value as an evaluation index that increases as the total time of the multipath generation period increases and increases as the time change rate of the high frequency component power increases. Good. The index output unit may output a value obtained by adjusting the ratio of the total time of the multipath generation period to the total time of the evaluation target period based on the time change rate of the power of the high frequency component as the evaluation value.

  In the present invention, the index output unit may output the evaluation index based on the sum of the temporal change rates of the power of a plurality of high frequency components in a predetermined high frequency band of the audio signal.

  In the present invention, the index output unit is based on the magnitude of the power of the high frequency component of the audio signal in the multipath generation period in addition to the total time of the multipath generation period and the time change rate of the power of the high frequency component. Output an evaluation index.

  In the present invention, an evaluation index for multipath noise is output based on the total time of the multipath generation period in the evaluation target period and the time change rate of the power of a predetermined high-frequency component of the audio signal in the multipath generation period. . Here, the present inventor has found that when multipath occurs, the power of multipath noise exists in the high frequency band in the power spectrum of the audio signal. The time change rate of the power of the predetermined high-frequency component of the audio signal during the multipath generation period is a value reflecting the change rate of the sound intensity of the multipath noise. For example, a short and strong multipath noise sound has a large rate of time change of the power, and the sensory evaluation result becomes worse. On the other hand, long and weak multipath noise has a small time change rate of the power, and the sensory evaluation result is improved. That is, the temporal change rate of the power of the high frequency component corresponds to the quality of the sensory evaluation result. According to the present invention, in addition to the total time of the multipath generation period, the evaluation index is output based on the time change rate of the power corresponding to the quality of the sensory evaluation result. The difference between the evaluation result and the sensory evaluation result can be suppressed.

  In the present invention, a value obtained by adjusting the ratio of the total time of the multipath generation period to the total time of the evaluation target period (multipath ratio) based on the time change rate of the power of the high frequency component is output as the evaluation value. For example, it is possible to relatively grasp the degree of influence of multipath noise on the total time of the evaluation target period.

  In the present invention, if the evaluation index is output based on the sum of the temporal change rates of the power of a plurality of high-frequency components in a predetermined high-frequency band of the audio signal, the time-based change rate of the power of the single high-frequency component Compared with the case where the evaluation index is output, the time change rate of the overall power in the high frequency band can be reflected, and the difference between the multipath evaluation result and the sensory evaluation result by the multipath evaluation device is suppressed. can do.

  In the present invention, if the evaluation index is output by adding the power of the high frequency component of the audio signal during the multipath generation period, the strength of the sound of multipath noise can be reflected in the evaluation index. It is possible to suppress the difference between the multipass evaluation result and the sensory evaluation result by the path evaluation device.

Schematic configuration diagram of a radio evaluation system using the multipath evaluation apparatus according to the embodiment A flowchart showing a method for calculating a multipath evaluation value Chart showing the power spectrum of each frame during the evaluation period The figure for demonstrating the number of a frame, the number of a multipath frame, and the number of a multipath generation | occurrence | production period

  Hereinafter, embodiments will be described in detail with reference to FIGS.

[1. About Radio Evaluation System]
First, the radio evaluation system 10 using the multipath evaluation apparatus 20 according to the present embodiment will be described. As shown in FIG. 1, the radio evaluation system 10 includes a signal output unit 11 that outputs a test signal (R / F signal), a radio 12 that receives the test signal from the signal output unit 11 and detects an audio signal. And a multipath evaluation device 20 that receives a sound signal from the radio 12 and calculates a multipath evaluation value as an evaluation index of multipath noise included in the sound signal. The radio 12 is a radio mounted on a vehicle, for example, and includes an antenna and a tuner. In the radio evaluation system 10, a cable connected to the output terminal of the signal output device 11 is connected to the antenna terminal of the radio 12 via a pseudo antenna (not shown). In the radio 12, a test signal is input from the antenna terminal to the tuner.

  The test signal is, for example, an R / F signal received in the field by a radio for data acquisition (may be the same as or different from the radio 12) (that is, a vehicle equipped with a radio for data acquisition) R / F signal received by the radio in the field during driving. The test signal is a signal that has not been detected (that is, a signal before being input to the tuner). The test signal is acquired in a field, for example, over a predetermined period and stored in a memory. This memory is attached to the signal output unit 11, and the signal output unit 11 outputs a test signal stored in the memory. The test signal is affected by the multipath generated during propagation of the R / F signal (radio wave) received in the field by the radio for data acquisition. The audio signal obtained by detecting the test signal includes multipath noise.

[2. About multipath evaluation equipment]
Next, the multipath evaluation device 20 will be described.

  The multipath evaluation device 20 uses the entire period of the time-series data of the audio signal input from the radio 12 as the evaluation target period, and the multipath in which the multipath has occurred during propagation of the R / F signal in the field from the evaluation target period Specify the period of occurrence. Then, the multipath evaluation device 20 calculates the multipath evaluation value based on the total time of the multipath generation period in the evaluation target period and the time change rate of the power of a predetermined high-frequency component of the audio signal in the multipath generation period. Calculate and output. The high frequency component is a frequency component belonging to a high frequency band (for example, a band of 10 kHz to 14 kHz) of the audio signal.

  The multipath evaluation device 20 increases the multipath evaluation value as the total time of the multipath generation period increases, and increases the multipath evaluation value as the time change rate of the power of the high frequency component increases. Multipath evaluation value is calculated. The multipath evaluation apparatus 20 calculates a value obtained by adjusting the multipath rate based on the time change rate of the power of the high frequency component as a multipath evaluation value. The multipath rate is a ratio of the total time of the multipath generation period to the total time of the evaluation target period. As illustrated in FIG. 1, the multipath evaluation apparatus 20 includes a sound collection unit 21, a frequency analysis unit 22, a multipath period specifying unit 23, and an index output unit 24.

  The multipath evaluation apparatus 20 is a computer unit in which a CPU, a RAM, a ROM, and the like are connected via a bus. The functional blocks 22 to 24 shown in FIG. 1 are functional blocks that function when the CPU executes program software stored in the ROM. These functional blocks do not need to be realized by a clearly separated program, and may be called by other programs as subroutines or functions. A part of the functional blocks may be realized by hardware means such as an LSI (Large Scale Integrated circuit), an IC (Integrated Circuit), or an FPGA (Field Programmable Gate Array).

  The sound collection unit 21 records an audio signal (digital time-series data) input from the radio 12. The frequency analysis unit 22 performs frequency analysis on the audio signal recorded in the sound collection unit 21 using FFT (Fast Fourier Transform) or the like. The frequency analysis unit 22 divides the evaluation target period of the time series data of the audio signal recorded in the sound collection unit 21 into a plurality of frames (time intervals), performs frequency analysis on the audio signal of each frame, For each frame, a power spectrum representing the frequency characteristic of the power of the audio signal is output.

  The multipath period specifying unit 23 is a multipath frame in which multipath is generated at the time of propagation of the R / F signal in the field, using the power spectrum of each frame for each frame divided by the frequency analysis unit 22. Multipath determination is performed to determine whether or not. Furthermore, the multipath period specifying unit 23 converts a frame determined to be a multipath frame in multipath determination into a continuous period (a small group of multipath frames) and a single multipath frame as a multipath generation period. As specified. The multipath period specifying unit 23 calculates a first threshold value and a second threshold value as determination threshold values used for multipath determination. The first threshold value and the second threshold value may be values set in advance in the multipath evaluation apparatus 20.

For each multipath frame in the multipath generation period specified by the multipath period specifying unit 23, the index output unit 24 uses a weighting factor (ΔBand_PWR _i in Equation 4 described later) based on a time change rate of power of a predetermined high frequency component. ) Is calculated. Then, the index output unit 24 calculates a value obtained by adjusting the multipath rate to the weighting coefficient of each multipath frame as a multipath evaluation value, and outputs it to the screen of the multipath evaluation apparatus 20.

[3. Multipath evaluation value calculation method]
Next, a method of calculating a multipath evaluation value (delta multipath rate) using the radio evaluation system 10 will be described with reference to the flowchart of FIG. Step S206 corresponds to a multipath period specifying step, and steps S207 and S208 correspond to an index output step.

  First, in step S201, the signal output unit 11 starts outputting a test signal. Next, in step S202, the radio 12 receives the test signal output from the signal output unit 11, and detects the audio signal by the tuner. An audio signal is extracted from the test signal by the radio 12. Next, in step S <b> 203, the sound collection unit 21 of the multipath evaluation device 20 records the audio signal output from the radio 12. The signal output unit 11 outputs a test signal over the entire period of the test signal. The radio 12 detects the audio signal over the entire period of the test signal. The sound collection unit 21 records an audio signal detected over the entire period of the test signal. For example, step S204 is performed after the recording of the audio signal is completed.

  In step S204, the frequency analysis unit 22 of the multipath evaluation apparatus 20 performs frequency analysis on the audio signal recorded in the sound collection unit 21 using FFT (Fast Fourier Transform) or the like. The frequency analysis unit 22 sets the entire period of the time series data of the audio signal recorded in the sound collection unit 21 as an evaluation target period, divides the evaluation target period into a plurality of frames (n frames), Frequency analysis is performed on the audio signal of each frame. As a result of the frequency analysis, a power spectrum representing the frequency characteristic of the power of the audio signal is obtained for each frame as shown in FIG. The power spectrum of each frame is created with, for example, a human audible range (for example, a band of 20 Hz to 14 kHz) as a target range.

  Hereinafter, the entire target range (human audible range) of the power spectrum is referred to as “overall frequency band (Overall)”. In addition, a band on the high frequency side (for example, a band of 10 kHz to 14 kHz) of the entire target range (human audible range) of the power spectrum is referred to as a “high frequency band (Band)”. The high frequency component of the audio signal is a frequency component belonging to the high frequency band. Further, as shown in FIG. 4, numbers i (1 ≦ i ≦ n) from 1 to n are assigned to all frames in the evaluation target period in order from the previous frame.

  In step S205, the frequency analysis unit 22 acquires the magnitude of power for a plurality of frequency components in the entire frequency band of the power spectrum of each frame i from the frequency analysis result. For example, the frequency interval between the plurality of frequency components is constant. The magnitude of power is the value on the vertical axis of the power spectrum shown in FIG. 3 and is expressed in units (dBV). As shown in FIG. 3, numbers j (1 ≦ j ≦ b) from 1 to b are assigned to the plurality of frequency components in the entire frequency band in order from the lowest frequency. The number j of the high-frequency component with the lowest frequency (for example, 10 kHz) is a (a ≦ b), and the number j of the high-frequency component with the highest frequency (for example, 14 kHz) is b.

Next, the frequency analysis unit 22 calculates the power temporal change rate ΔPWR _{i, j} in each frequency component j of the power spectrum of each frame i using Equation 1. Time rate of change DerutaPWR _{i, j} of the power, by the time _{T i} of frame i, more is calculated in dividing the power PWR _{i + 1, j} of frame i + 1, the power PWR _i frame _i, the difference between the _j (See FIG. 3 for T _i , PWR _{i + 1, j} , and PWR _{i, j} ). Note that the time of each frame is equal.

  In step S206, a first specifying operation for specifying a multipath candidate frame from all the frames is performed using each of all the frames in the evaluation target period as a determination section, and then all of the multiple specified by the first specifying operation are performed. Using each of the path candidate frames as a determination section, a second specifying operation for specifying a multipath frame from all the multipath candidate frames is performed. In step S206, multipath determination is performed by the first specific operation and the second specific operation.

In the first specifying operation, first, the multipath period specifying unit 23 determines the power values (Ave_Overall, MAX_Overall) to be input to the right side of Expression 2 from the magnitude of the power of each frequency component j of each frame i acquired in step S205. ) And the obtained value is substituted into Equation 2 to calculate the first threshold value T1. Formula 2 is an example of a method for calculating the first threshold value T1.

  In Equation 2, MAX_Overall represents the maximum value of power in all frequency bands of the power spectrum of all frames in the evaluation target period, and Ave_Overall represents the average value of power in all frequency bands of the power spectrum of all frames in the evaluation target period. Represent. A is a first set value (for example, 70%), and is set in advance in the multipath evaluation apparatus 20, for example. The first threshold value T1 is set to a value obtained by apportioning a predetermined ratio between the maximum value of power and the average value of power in all frequency bands of the power spectrum of all frames.

  In the first specifying operation, after the calculation of the first threshold T1, the multipath period specifying unit 23 sets the average power Overall_PWR (i) in the entire frequency band of the power spectrum to the first threshold T1 for each frame i. It is determined whether or not the first condition of exceeding is satisfied, and a frame that satisfies the first condition is specified as a multipath candidate frame. In the first specifying operation, a frame having a relatively high average power value in all frequency bands among all frames is specified as a multipath candidate frame.

In the second specifying operation, first, the multipath period specifying unit 23 determines the power values (Ave_Band_PWR, MAX_Band_PWR) to be input to the right side of Equation 3 from the power level of each high-frequency component j of each frame i acquired in step S205. ) And the obtained value is substituted into Equation 3 to calculate the second threshold T2. Formula 3 is an example of a method for calculating the second threshold T2.

  In Equation 3, MAX_Band_PWR represents the maximum value of power in the high frequency band of the power spectrum of all multipath candidate frames, and Ave_Band_PWR represents the average value of power in the high frequency band of the power spectrum of all multipath candidate frames. B is a second set value (for example, 90%), and is set in advance in the multipath evaluation apparatus 20, for example. The second threshold value T2 is set to a value that is proportionally distributed between the maximum power value and the average power value in the high frequency band of the power spectrum of all multipath candidate frames.

  In the second specifying operation, after the calculation of the second threshold T2, the multipath period specifying unit 23 sets the average power Band_PWR (i) in the high frequency band of the power spectrum to the second threshold for each multipath candidate frame i. It is determined whether or not the second condition of exceeding T2 is satisfied, and a multipath candidate frame that satisfies the second condition is identified as a multipath frame. In the second specifying operation, a frame having a relatively high average power value in a high frequency band among all multipath candidate frames is specified as a multipath frame.

  In step S206, a frame that satisfies both the first condition and the second condition is identified as a multipath frame. Then, the multipath period specifying unit 23 generates a small group of a plurality of multipath frames continuous along the time axis and a single multipath frame (multiple frames in which the immediately preceding and following frames are not determined to be multipath frames). (Path frame) is specified as a multipath occurrence period. In a small group of multipath frames, the multipath generation period is from the start time of the first multipath frame to the end time of the last multipath frame. In a single multipath frame, a multipath generation period is from the start time to the end time of the multipath frame. When detecting a plurality of multipath generation periods, the multipath period specifying unit 23 specifies a plurality of multipath generation periods. Hereinafter, a case where a plurality of multipath generation periods are specified will be described. As shown in FIG. 4, in the evaluation target period, numbers x (1 ≦ x ≦ m) from 1 to m are assigned in order from the previous multipath generation period. In each multipath generation period, a number y (1 ≦ y ≦ k) from 1 to k is assigned in order from the previous multipath frame.

In step S207, for each multipath generation period, the index output unit 24 associates the number y of each multipath frame with the number i of the frame, and outputs the power of each high frequency component j of the power spectrum of each multipath frame y. The time change rate ΔPWR _{y, j} is associated with ΔPWR _{i, j} calculated by Equation 1. Then, the index output unit 24 uses Equation 4 for each multipath frame y in each multipath generation period for the sum of the temporal change rates of the power of all the high frequency components j (from the high frequency component a to the high frequency component b). The sum of the power temporal change rates) is calculated as a weighting coefficient ΔBand_PWR _y of each multipath frame y.

In step S208, the index output unit 24 calculates the multipath evaluation value X using Equation 5 and Equation 6. According to Equation 5, for each multipath generation period x, the absolute value of the sum of the weighting factors ΔBand_PWR _i (the sum of the weighting factors of all the multipath frames) from the multipath frame 1 to the multipath frame k is the sum of the frames. Calculated as the value ΔBand_PWRx. Further, according to Equation 6, the sum of the frame total value ΔBand_PWRx from the multipath generation period 1 to the multipath generation period m (the sum of the frame total values of all multipath generation periods) is calculated as the total number n of frames in the evaluation target period. The multipath evaluation value X is calculated by dividing by.

The numerator on the right side of Equation 6 is the total value of the weighting factors ΔBand_PWR _i of all the multipath frames in the evaluation target period. This total value is equal to the total value of values obtained by multiplying the time of each multipath frame by the weight coefficient of each multipath frame, where the time of each multipath frame is 1. Therefore, the multipath evaluation value X obtained by dividing the numerator on the right side of Equation 6 by the total number of frames n adjusts the multipath rate by weighting the time of each multipath frame with the weighting coefficient of each multipath frame. It can be said that.

  When the multipath evaluation value is calculated in step S208, the multipath evaluation apparatus 20 presents the multipath evaluation value to the user by displaying the multipath evaluation value X on the screen. The multipath evaluation device 20 calculates and outputs a multipath evaluation value for an audio signal obtained as a result of detecting the same test signal by a radio other than the radio 12. The user relatively evaluates the performance of the part that suppresses multipath noise in each radio by comparing the multipath evaluation value for the audio signal of each radio (the test signal is the same) between multiple radios. can do.

[4. Effects of the embodiment]
In the present embodiment, the multipath evaluation value is calculated based on the total time of the multipath generation period in the evaluation target period and the time change rate of the power of a predetermined high-frequency component of the audio signal in the multipath generation period. .

  Here, as described above, the temporal change rate of the power of a predetermined high-frequency component of the audio signal in the multipath generation period is a value reflecting the change rate of the sound intensity of the multipath noise. A short and strong multipath noise sound has a large rate of time change of the power, resulting in poor sensory evaluation results. On the other hand, long and weak multipath noise has a small time change rate of the power, and the sensory evaluation result is improved. Specifically, when the noise “Zaza”, “Za” or “Petit” is generated due to multipath noise, the rate of time change of the power is large and the sensory evaluation result becomes poor. When the noise “sir” is generated due to multipath noise, the time change rate of the power is small and the sensory evaluation result is improved. That is, the time change rate of the power corresponds to the quality of the sensory evaluation result. According to the present embodiment, in order to output the multipath evaluation value based on the time change rate of the power corresponding to the quality of the sensory evaluation result in addition to the total time of the multipath generation period, the multipath evaluation apparatus It can suppress that the multipass evaluation result by 20 and the sensory evaluation result differ.

  In this embodiment, since the value obtained by adjusting the multipath rate based on the time change rate of the power of the high-frequency component is output as an evaluation value, the degree of influence of multipath noise on the total time of the evaluation target period is relative. Can be grasped.

  In this embodiment, since the evaluation index is output based on the sum of the temporal change rates of the power of a plurality of high-frequency components in a predetermined high-frequency band of the audio signal, the overall temporal change rate of the power in the high-frequency band is calculated. It can reflect, and it can control that the multipass evaluation result by the multipass evaluation apparatus 20 and the sensory evaluation result differ.

[5. Other Embodiments]
In the above embodiment, the multipath evaluation value X is calculated by dividing by the total number of frames n in the evaluation target period in Expression 6, but without being divided by the total number of frames n in the evaluation target period as in Expression 7. A multipath evaluation value X ′ may be calculated.

  In the embodiment described above, the total time of multipath generation time (or multipath rate) and the sum of weight coefficients of all multipath frames may be displayed on the screen as multipath noise evaluation indices. Good.

  In the above embodiment, the sum of the temporal change rates of the power of a plurality of high-frequency components is used as the weighting coefficient of each multipath frame, but the temporal change rate of the power of a single high-frequency component is the weight of each multipath frame. It is good also as a coefficient.

  In the above embodiment, a cepstrum analysis may be performed in order to specify a multipath frame. In the cepstrum analysis, the presence or absence of a cepstrum (a feature vector representing a human voice signal) is determined. For example, it may be determined whether or not the third condition “no cepstrum” is satisfied, and a frame in which all of the first condition, the second condition, and the third condition are satisfied may be specified as a multipath frame.

  In the embodiment, in addition to the total time of the multipath generation period in the evaluation target period and the time change rate of the power of the predetermined high-frequency component of the audio signal in the multipath generation period, the multipath generation period The multipath evaluation value may be calculated based on the magnitude of the power of the high-frequency component of the audio signal at (for example, the average power in the high-frequency band). Thereby, the sound intensity of multipath noise can be reflected in the multipath evaluation value.

  In the embodiment described above, an audio signal detected by a device other than a radio (for example, a television) may be input to the multipath evaluation device 20 to calculate a multipath evaluation value.

  In the above embodiment, the multipath evaluation value is calculated using the time change rate of the power (dBV) value on the power spectrum as it is, but other units (for example, dB, V, etc.) that can be converted from the power (dBV) are calculated. The multipath evaluation value may be calculated based on the time change rate of the numerical value of) (a value representing the strength of the audio signal).

  The present invention is applicable to a multipath evaluation apparatus and a multipath evaluation method for evaluating multipath noise.

DESCRIPTION OF SYMBOLS 10 Radio evaluation system 11 Signal output device 12 Radio 20 Multipath evaluation apparatus 23 Multipath period specific | specification part 24 Index output part

Claims (6)

A multipath evaluation apparatus for evaluating multipath noise contained in an audio signal,
A multipath period identifying unit that identifies a multipath occurrence period in which multipath has occurred in an evaluation target period of the time-series data of the audio signal;
An index for outputting an evaluation index of multipath noise based on a total time of the multipath generation period in the evaluation target period and a time change rate of power of a predetermined high frequency component of the audio signal in the multipath generation period And a multipath evaluation device.   The index output unit outputs, as the evaluation index, an evaluation value that increases as the total time of the multipath generation period increases and increases as the time change rate of the power of the high-frequency component increases. The multipath evaluation apparatus according to claim 1.   The index output unit outputs, as the evaluation value, a value obtained by adjusting a ratio of the total time of the multipath generation period to the total time of the evaluation target period based on a time change rate of the power of the high-frequency component. The multipath evaluation apparatus according to claim 2, wherein:   2. The multipath according to claim 1, wherein the index output unit outputs the evaluation index based on a sum of temporal change rates of power of a plurality of high frequency components in a predetermined high frequency band of the audio signal. Evaluation device.   In addition to the total time of the multipath generation period and the time change rate of the power of the high frequency component, the index output unit is based on the magnitude of the power of the high frequency component of the audio signal in the multipath generation period. The multipath evaluation apparatus according to claim 1, wherein the evaluation index is output. A multipath evaluation method for evaluating multipath noise contained in an audio signal,
A multipath period identifying step for identifying a multipath occurrence period in which multipath has occurred in an evaluation target period of the time-series data of the audio signal;
An index for outputting an evaluation index of multipath noise based on a total time of the multipath generation period in the evaluation target period and a time change rate of power of a predetermined high frequency component of the audio signal in the multipath generation period An output step.

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