Audio processing apparatus and audio processing method

Abstract

To detect noise inside a vehicle so as to output sound with more appropriate volume and sound quality in terms of audibility.SOLUTION: An acoustic processing device to be mounted on a vehicle comprises: a sound source removal section for outputting a noise level which is obtained by subtracting a sound source level from a microphone level; a speed noise level calculation section for outputting a speed noise level which indicates frequency characteristics of noise based on a speed of the vehicle; a volume sound source level calculation section for outputting a volume sound source level which indicates frequency characteristics based on a volume of a predetermined sound source signal; an SN ratio calculation section for outputting an SN ratio being the ratio between the volume sound source level and the speed noise level; and an output selection section for selecting any one of estimated noise level candidates including a level related to the noise level and the speed noise level on the basis of the SN ratio, so as to output the selected level as an estimated noise level. The microphone level indicates frequency characteristics of a microphone signal collected by a microphone provided inside the vehicle and the sound source level indicates frequency characteristics of a sound source signal to be output from a speaker provided inside the vehicle.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to an acoustic processing apparatus and an acoustic processing method.

Background Art

[0002] The noise level inside a vehicle differs between when the vehicle is stopped and when it is running. Therefore, in an acoustic device mounted in a vehicle, even if the volume of the acoustic device is adjusted based on the noise level at the time of stopping, when the noise level increases as the vehicle starts running, particularly the very low volume portion of the reproduced sound may be masked, and there may be a feeling of insufficient volume.

[0003] Patent Document 1 discloses using a microphone installed inside the vehicle to detect noise across the entire voice band, and when it is difficult to detect noise due to the large influence of the reproduced sound, estimating the noise volume using the vehicle's running speed as a clue, enabling noise detection with good correspondence to the sense of hearing, and an in-vehicle acoustic device equipped with an automatic volume and sound quality adjustment function that is appropriate in terms of the sense of hearing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, there is a demand for acoustic output with more appropriate volume and sound quality in terms of the sense of hearing inside the vehicle.

[0006] An object of the present disclosure is to output sound with more appropriate volume and sound quality in terms of the sense of hearing inside the vehicle.

Means for Solving the Problems

[0007] An acoustic processing device according to one aspect of the present disclosure is an acoustic processing device mounted on a vehicle, comprising: a sound source removal unit that outputs a noise level obtained by subtracting a sound source level from a microphone level; a speed noise level calculation unit that outputs a speed noise level indicating a frequency characteristic of noise based on the speed of the vehicle; a volume sound source level calculation unit that outputs a volume sound source level indicating a frequency characteristic based on the volume of a predetermined sound source signal; an SN ratio calculation unit that outputs an SN ratio which is a ratio of the volume sound source level to the speed noise level; and an output selection unit that selects any one of a level related to the noise level and an estimated noise level candidate including the speed noise level based on the SN ratio and outputs it as an estimated noise level. The microphone level indicates the frequency characteristic of a microphone signal collected by a microphone provided inside the vehicle, and the sound source level indicates the frequency characteristic of a sound source signal output from a speaker provided inside the vehicle.

[0008] An acoustic processing device according to one aspect of the present disclosure is an acoustic processing device mounted on a vehicle, comprising: a sound source removal unit that outputs a noise level obtained by subtracting a sound source level from a microphone level; a speed noise level calculation unit that outputs a speed noise level indicating a frequency characteristic of noise based on the speed of the vehicle; a volume sound source level calculation unit that outputs a volume sound source level indicating a frequency characteristic based on the volume of a predetermined sound source signal; a microphone level limitation unit that outputs a limited microphone level which is the microphone level limited based on the speed noise level; an SN ratio calculation unit that outputs an SN ratio which is a ratio of the volume sound source level to the limited microphone level; and an output selection unit that selects any one of the microphone level, the noise level, and the limited microphone level based on the SN ratio and outputs it as an estimated noise level. The microphone level indicates the frequency characteristic of a microphone signal collected by a microphone provided inside the vehicle, and the sound source level indicates the frequency characteristic of a sound source signal output from a speaker provided inside the vehicle.

[0009] An acoustic processing apparatus according to an aspect of the present disclosure is an acoustic processing apparatus mounted on a vehicle, which outputs a noise signal obtained by subtracting a sound source signal from a microphone signal collected by a microphone provided inside the vehicle using an adaptive filter; a speed noise level calculation unit that outputs a speed noise level indicating the frequency characteristics of noise based on the speed of the vehicle; a volume sound source level calculation unit that outputs a volume sound source level indicating the frequency characteristics based on the volume of a predetermined sound source signal; an SN ratio calculation unit that outputs an SN ratio which is the ratio of the volume sound source level to the speed noise level; and an output selection unit that selects any one of a microphone level indicating the frequency characteristics of the microphone signal, a noise level indicating the frequency characteristics of the noise signal, and the speed noise level based on the SN ratio and outputs it as an estimated noise level. The sound source signal is output from a speaker provided inside the vehicle.

[0010] An acoustic processing method according to an aspect of the present disclosure outputs a noise level obtained by subtracting a sound source level from a microphone level, outputs a speed noise level indicating the frequency characteristics of noise based on the speed of the vehicle, outputs a volume sound source level indicating the frequency characteristics based on the volume of a predetermined sound source signal, outputs an SN ratio which is the ratio of the volume sound source level to the speed noise level, selects any one of the level related to the noise level and the speed noise level based on the SN ratio and outputs it as an estimated noise level. The microphone level indicates the frequency characteristics of a microphone signal collected by a microphone provided inside the vehicle, and the sound source level indicates the frequency characteristics of a sound source signal output from a speaker provided inside the vehicle.

[0011] These general or specific aspects may be implemented by a system, apparatus, method, integrated circuit, computer program, or recording medium, or may be implemented by any combination of a system, apparatus, method, integrated circuit, computer program, and recording medium.

Advantages of the Invention

[0012] According to the present disclosure, in-vehicle sound can be output with a more appropriate volume and sound quality in terms of auditory sensation.

Brief Description of the Drawings

[0013]

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Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with appropriate reference to the drawings. However, a more detailed description than necessary may be omitted. For example, detailed descriptions of well-known matters and duplicate descriptions of substantially the same configurations may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims thereby.

[0015] (This embodiment) <Configuration of the acoustic processing device> FIG. 1 is a block diagram showing a configuration example of an acoustic processing device 10 according to the present embodiment.

[0016] The acoustic processing device 10 is mounted on a vehicle and outputs a sound source signal obtained from a sound source as sound into the vehicle interior. As shown in FIG. 1, the acoustic processing device 10 includes a sound source signal input unit 11, a noise follow type equalizer 12, a volume amplification unit 13, a speaker 14, a microphone signal input unit 15, a speed input unit 16, a volume input unit 17, a noise level estimation unit 18, a sound source level analysis unit 19, and a compensation amount calculation unit 20.

[0017] A sound source signal is input to the sound source signal input unit 11. Examples of sound sources include a radio, cassette tape, CD (Compact Disc), DVD (Digital Versatile Disc), BD (Blu-ray (registered trademark) Disc), USB memory, SD card, Internet streaming, and the like. That is, the sound source signal is a time signal of sound reproduced from a sound source.

[0018] The noise tracking equalizer 12 adjusts the frequency characteristics of the sound source signal input to the sound source signal input unit 11 based on the compensation amount output from the compensation amount calculation unit 20 described later, and outputs the adjusted sound source signal. Hereinafter, the frequency characteristics of the sound source signal are referred to as the sound source level. The compensation amount indicates an amount for compensating the sound source level that has become difficult to hear due to noise generated inside the vehicle during driving of the vehicle or the like so that it becomes an easy-to-hear sound source level. That is, the noise tracking equalizer 12 adjusts the sound source level that has become difficult to hear due to noise to an easy-to-hear sound source level based on the compensation amount. Further, since the compensation amount is an amount calculated based on the noise inside the vehicle, the compensation amount also changes in response to changes in the noise. Therefore, the noise tracking equalizer 12 can use the compensation amount to adjust the sound source level to be easy to hear following changes in the noise. As a result, even when there is noise inside the vehicle, the passengers inside the vehicle can easily hear the sound generated by reproducing the sound source.

[0019] The volume amplification unit 13 amplifies the sound source signal output from the noise tracking equalizer 12 based on the volume input to the volume input unit 17, and outputs the amplified sound source signal. Note that the volume amplification unit 13 may be read as an amplifier.

[0020] The speaker 14 is installed inside the vehicle and outputs the sound source signal output from the volume amplification unit 13 as sound.

[0021] A microphone signal is input to the microphone signal input unit 15. The microphone signal is a time signal of sound collected by a microphone installed inside the vehicle. Therefore, the microphone signal may include a signal of sound output from the speaker 14 into the vehicle and a signal of noise audible inside the vehicle.

[0022] A value indicating the speed of the vehicle is input to the speed input unit 16. The speed of the vehicle may be automatically acquired from a vehicle speed sensor mounted on the vehicle.

[0023] A value indicating the volume when the sound source signal is output as sound from the speaker 14 is input to the volume input unit 17. The volume may be input by a passenger inside the vehicle. For example, the passenger can operate the audio processing device 10 to increase or decrease the volume of the sound output from the speaker 14.

[0024] Based on the microphone signal input to the microphone signal input unit 15, the sound source signal output from the volume amplification unit 13, the speed input to the speed input unit 16, and the volume input to the volume input unit 17, the noise level estimation unit 18 estimates a noise level indicating the frequency characteristics of the noise inside the vehicle and outputs it as an estimated noise level. Details of the noise level estimation unit 18 will be described later.

[0025] The sound source level analysis unit 19 analyzes the frequency characteristics of the sound source signal output from the volume amplification unit 13 and outputs a sound source level indicating the analyzed frequency characteristics. Note that the sound source level analysis unit 19 may perform predetermined weighting on the sound source level and output the sound source level after the weighting.

[0026] The compensation amount calculation unit 20 calculates a compensation amount based on the sound source level output from the sound source level analysis unit 19 and the estimated noise level output from the noise level estimation unit 18, and outputs the calculated compensation amount. For example, the compensation amount calculation unit 20 calculates a compensation amount that increases the sound source level in a frequency band where the difference between the sound source level and the estimated noise level is less than a predetermined threshold.

[0027] Note that the audio processing device 10 may include a processor, a memory, a storage, and the like. The noise tracking equalizer 12, the noise level estimation unit 18, the sound source level analysis unit 19, and the compensation amount calculation unit 20 may be realized by the processor cooperating with the memory, the storage, and the like to execute a predetermined computer program. Alternatively, at least one of the noise tracking equalizer 12, the noise level estimation unit 18, the sound source level analysis unit 19, and the compensation amount calculation unit 20 may be realized by an integrated circuit. Examples of the integrated circuit include LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), and FPGA (Field-Programmable Gate Array).

[0028] <First Configuration Example> FIG. 2 is a block diagram showing a first configuration example of the noise level estimation unit 18 according to the present embodiment.

[0029] The noise level estimation unit 18 according to the first configuration example includes a microphone level analysis unit 31, a sound source level analysis unit 32, a sound source removal unit 33, a speed noise level calculation unit 34, a volume sound source level calculation unit 35, an SN ratio calculation unit 36, and an output selection unit 37.

[0030] The microphone level analysis unit 31 analyzes the frequency characteristics of the microphone signal input to the microphone signal input unit 15 and outputs a microphone level indicating the analyzed frequency characteristics.

[0031] The sound source level analysis unit 32 analyzes the frequency characteristics of the sound source signal output from the volume amplification unit 13 and outputs a sound source level indicating the analyzed frequency characteristics. Note that the sound source level analysis unit 32 may perform predetermined weighting on the sound source level and output the sound source level after the weighting.

[0032] The sound source removal unit 33 calculates the noise level by removing the sound source level output from the sound source level analysis unit 32 from the microphone level output from the microphone level analysis unit 31. For example, the sound source removal unit 33 includes a subtraction processing unit 38, and the subtraction processing unit 38 outputs the result of subtracting the sound source level (S1) from the microphone level (M) as the noise level (M - S1).

[0033] The speed noise level calculation unit 34 calculates the speed noise level based on the vehicle speed input to the speed input unit 16 and outputs the calculated speed noise level (N2). The speed noise level indicates the frequency characteristics of the noise inside the vehicle at a certain speed. For example, the provider of the acoustic processing device 10 measures the noise level inside the vehicle at each speed and pre-generates a speed noise level table associating each speed with the noise level measured at that speed. Then, the provider pre-stores the speed noise level table in the memory or storage of the acoustic processing device 10 or the like. The speed noise level calculation unit 34 calculates the speed noise level corresponding to the speed input to the speed input unit 16 using the speed noise level table.

[0034] The volume sound source level calculation unit 35 calculates the volume sound source level based on the volume input to the volume input unit 17 and outputs the calculated volume sound source level (S2). The volume sound source level indicates the frequency characteristics of a predetermined sound source signal at a certain volume. For example, the provider of the acoustic processing device 10 measures the sound source level of a predetermined sound source signal at each volume and pre-generates a volume sound source level table associating each volume with the sound source level measured at that volume. Then, the provider pre-stores the volume sound source level table in the memory or storage of the acoustic processing device 10 or the like. The volume sound source level calculation unit 35 calculates the volume sound source level corresponding to the volume input to the volume input unit 17 using the volume sound source level table.

[0035] The SN ratio calculation unit 36 calculates the ratio of the volume sound source level (S2) output from the volume sound source level calculation unit 35 to the speed noise level (N2) output from the speed noise level calculation unit 34 as the SN ratio, and outputs the calculated SN ratio.

[0036] Based on the SN ratio output from the SN ratio calculation unit 36, the output selection unit 37 selects any one of the microphone level (M) output from the microphone level analysis unit 31, the noise level (M - S1) output from the sound source removal unit 33, and the speed noise level (N2) output from the speed noise level calculation unit 34, and outputs it as the estimated noise level. For example, the output selection unit 37 makes the selections shown in the following (A1) to (A3).

[0037] (A1) When the SN ratio is less than a predetermined threshold Th0, the output selection unit 37 selects the microphone level (M) and outputs it as the estimated noise level. (A2) When the SN ratio is greater than a predetermined threshold Th1, the output selection unit 37 selects the speed noise level (N2) and outputs it as the estimated noise level. Note that the threshold Th1 is greater than the threshold Th0. (A3) When the SN ratio does not fall under either of the above (A1) and (A2), the output selection unit 37 selects the noise level (M - S1) and outputs it as the estimated noise level. That is, when the SN ratio is greater than or equal to the threshold Th0 and less than or equal to the threshold Th1, the output selection unit 37 selects the noise level (M - S1) and outputs it as the estimated noise level.

[0038] Note that the above microphone level may be included in the level related to the microphone level. The above noise level may be included in the level related to the noise level. Also, the level related to the microphone level, the level related to the noise level, and the speed noise level may be included in the estimated noise level candidates.

[0039] Next, in this embodiment, the reason why the output selection unit 37 makes the selections as in the above (A1) to (A3) will be described.

[0040] The noise level (M - S1) shown in (A3) above is calculated by subtracting the sound source level (S1) from the microphone level (M) on the assumption that energy addition holds between the sound source signal and the noise signal. Here, the fact that energy addition holds between the sound source signal and the noise signal means that the microphone signal is represented by the simple addition of the sound source signal and the noise signal. However, when the sound source signal is sufficiently larger than the noise signal, simple energy addition does not hold between the sound source signal and the noise signal. Therefore, in this case, the noise level (M - S1) calculated by subtracting the sound source level (S1) from the microphone level (M) may include a large error with respect to the actual noise level. When the compensation amount calculation unit 20 calculates the compensation amount using the noise level (M - S1) that includes a large error, a compensation amount that greatly deviates from the actual noise level is calculated. When the noise tracking equalizer 12 adjusts the sound source level using such a compensation amount that greatly deviates from the actual noise level, for example, the sound source level is made unnecessarily large, and problems such as the sound being output at an inappropriate volume and sound quality in terms of auditory sensation occur.

[0041] On the other hand, in the present embodiment, when the sound source signal is sufficiently larger than the noise signal, that is, when the signal-to-noise ratio is larger than a predetermined threshold Th1, the output selection unit 37 selects and outputs the speed noise level (N2) as shown in (A2) above. Therefore, when the sound source signal is sufficiently larger than the noise signal, the compensation amount calculation unit 20 calculates the compensation amount using the speed noise level (N2), so problems such as the sound being output at an inappropriate volume and sound quality in terms of auditory sensation as in the case of using the above noise level (M - S1) are less likely to occur.

[0042] The reason why the output selection unit 37 makes the selection shown in (A1) when the sound source signal is sufficiently smaller than the noise signal, that is, when the signal-to-noise ratio is smaller than a predetermined threshold Th0, is as follows. That is, when the signal-to-noise ratio is smaller than the predetermined threshold Th0, since the noise component is dominant in the microphone level (M), it can be estimated that the frequency characteristics of the noise in the vehicle are appropriately represented.

[0043] According to the first configuration example, the noise level estimation unit 18 can provide the compensation amount calculation unit 20 with an estimated noise level that more appropriately represents the in-vehicle noise. Therefore, the acoustic processing device 10 can appropriately adjust the sound source signal that has become difficult to hear due to the in-vehicle noise into a more audible sound source signal and output it from the speaker 14 as sound. That is, the acoustic processing device 10 can output sound with a more appropriate volume and sound quality in terms of auditory sensation with respect to the in-vehicle noise.

[0044] <Second Configuration Example> FIG. 3 is a block diagram showing a second configuration example of the noise level estimation unit 18 according to the present embodiment.

[0045] The noise level estimation unit 18 according to the second configuration example includes a microphone level analysis unit 31, a sound source removal unit 33, a speed noise level calculation unit 34, a volume sound source level calculation unit 35, an SN ratio calculation unit 36, an output selection unit 37, and a noise level analysis unit 39.

[0046] The microphone level analysis unit 31, the speed noise level calculation unit 34, the volume sound source level calculation unit 35, and the SN ratio calculation unit 36 perform the same processing as in the first configuration example.

[0047] The sound source removal unit 33 includes a subtraction processing unit 38, an adaptive filter unit 40, and an LMS (Least Mean Squares) algorithm unit 41.

[0048] The adaptive filter unit 40 applies a variable filter based on the correction coefficient output from the LMS algorithm unit 41 to the sound source signal output from the volume amplification unit 13 and outputs the sound source signal after the variable filter is applied.

[0049] The subtraction processing unit 38 outputs a noise signal obtained by subtracting the sound source signal output from the adaptive filter unit 40 from the microphone signal input to the microphone signal input unit 15.

[0050] The LMS algorithm unit 41 calculates a correction coefficient by the LMS algorithm based on the sound source signal output from the volume amplification unit 13 and the noise signal output from the subtraction processing unit 38, and outputs it to the adaptive filter unit 40. Note that the method for calculating the correction coefficient is not limited to the LMS algorithm, and other adaptive algorithms may be used.

[0051] The noise level analysis unit 39 analyzes the frequency characteristics of the noise signal output from the subtraction processing unit 38, and outputs a noise level (M-S1) indicating the analyzed frequency characteristics.

[0052] Based on the SNR output from the SNR calculation unit 36, the output selection unit 37 selects any one of the microphone level (M) output from the microphone level analysis unit 31, the noise level (M-S1) output from the noise level analysis unit 39, and the speed noise level (N2) output from the speed noise level calculation unit 34, and outputs it as the estimated noise level. Note that the output selection unit 37 may perform the selection according to (A1) to (A3) described in the first configuration example.

[0053] According to the second configuration example, the noise level estimation unit 18 can provide the compensation amount calculation unit 20 with an estimated noise level that more appropriately represents the noise inside the vehicle. Therefore, the acoustic processing device 10 can adjust a sound source signal that is difficult to hear due to the noise inside the vehicle into a sound source signal that is easier to hear, and output it from the speaker 14 as sound.

[0054] Note that when the noise signal is sufficiently larger than the sound source signal, or when the sound source signal is sufficiently smaller than the noise signal, it is considered that the removal performance of the adaptive filter unit 40 for the sound source signal decreases. In this case, the sound source removal unit 33 may be configured to not use the adaptive filter unit 40 when the removal performance may decrease, and to use the adaptive filter unit 40 when it is considered that the removal performance does not decrease. Thereby, since the error of the noise signal output from the sound source removal unit 33 is reduced, the acoustic processing device 10 can output sound with a more appropriate volume and sound quality in terms of the sense of hearing.

[0055] <The Third Configuration Example> FIG. 4 is a block diagram showing a third configuration example of the noise level estimation unit 18 according to the present embodiment.

[0056] The noise level estimation unit 18 according to the third configuration example includes a microphone level analysis unit 31, a sound source level analysis unit 32, a sound source removal unit 33, a speed noise level calculation unit 34, a volume sound source level calculation unit 35, an SN ratio calculation unit 36, an output selection unit 37, and a microphone level limitation unit 42.

[0057] The microphone level analysis unit 31, the sound source level analysis unit 32, the sound source removal unit 33, the volume sound source level calculation unit 35, and the speed noise level calculation unit 34 perform the same processing as in the first configuration example.

[0058] The microphone level limitation unit 42 limits the upper and lower limits of the microphone level (M) output from the microphone level analysis unit 31 based on the speed noise level (N2) output from the speed noise level calculation unit 34, and outputs the limited microphone level as the limited microphone level (M2). For example, the microphone level limitation unit 42 performs the following processes (B1) to (B3).

[0059] (B1) When the microphone level (M) is greater than the level obtained by adding a predetermined value Max1 to the speed noise level (N2), the microphone level limitation unit 42 outputs the level obtained by adding the predetermined value Max1 to the speed noise level (N2) as the limited microphone level (M2). (B2) When the microphone level (M) is less than the level obtained by subtracting a predetermined value Min1 from the speed noise level (N2), the microphone level limitation unit 42 outputs the level obtained by subtracting the predetermined value Min1 from the speed noise level (N2) as the limited microphone level (M2). (B3) If the microphone level (M) does not meet either of the above (B1) and (B2), the microphone level limiter 42 outputs the microphone level (M) as the limited microphone level (M2) as it is. That is, when the microphone level (M) is less than or equal to the level obtained by adding a predetermined value Max1 to the speed noise level (N2) and greater than or equal to the level obtained by subtracting a predetermined value Min1 from the speed noise level (N2), the microphone level limiter 42 outputs the microphone level (M) as the limited microphone level (M2) as it is.

[0060] The SN ratio calculation unit 36 calculates the ratio between the volume sound source level (S2) output from the volume sound source level calculation unit 35 and the limited microphone level (M2) output from the microphone level limiter 42, and outputs the calculated ratio as the SN ratio.

[0061] Based on the SN ratio output from the SN ratio calculation unit 36, the output selection unit 37 selects one of the microphone level (M) output from the microphone level analysis unit 31, the noise level (M - S1) output from the sound source removal unit 33, and the limited microphone level (M2) output from the microphone level limiter 42, and outputs it as the estimated noise level. For example, the output selection unit 37 makes the selections shown in the following (C1) to (C3).

[0062] (C1) When the SN ratio is less than a predetermined threshold Th0, the output selection unit 37 selects the microphone level (M) and outputs it as the estimated noise level. (C2) When the SN ratio is greater than a predetermined threshold Th1, the output selection unit 37 selects the limited microphone level (M2) and outputs it as the estimated noise level. Note that the threshold Th1 is greater than the threshold Th0. (C3) When the SN ratio does not meet either of the above (C1) and (C2), the output selection unit 37 selects the noise level (M - S1) and outputs it as the estimated noise level. That is, when the SN ratio is greater than or equal to the threshold Th0 and less than or equal to the threshold Th1, the output selection unit 37 selects the noise level (M - S1) and outputs it as the estimated noise level.

[0063] As in the first configuration example, when calculating the compensation amount using the speed noise level (N2) as the estimated noise level, the change in noise caused by the difference in the road surface on which the vehicle is traveling is not reflected in the compensation amount. On the other hand, the microphone level includes noise components that change depending on the road surface. Therefore, by calculating the compensation amount after using the microphone level as the estimated noise level, it is possible to reflect the change in noise caused by the difference in the road surface in the compensation amount. On the other hand, the microphone level may include sudden noise. Examples of sudden noise include the sound when a passenger touches the microphone, a sudden loud voice of a passenger, and the sound when the vehicle crosses a step. If the compensation amount is calculated using the microphone level that includes such sudden noise as the estimated noise level, and the noise tracking equalizer 12 adjusts the sound source level using the compensation amount calculated in this way, problems such as unnecessarily increasing the sound source level may occur. Therefore, in the third configuration example, as described above, the microphone level limiting unit 42 is provided, and as shown in (C2) above, when the signal-to-noise ratio is greater than the threshold Th1, the limited microphone level (M2) is selected and output to suppress the occurrence of such problems.

[0064] Note that the signal-to-noise ratio calculation unit 36 may calculate the signal-to-noise ratio using the sound source level (S1) output from the sound source level analysis unit 32 instead of the volume sound source level (S2). Thereby, for example, even in the case of a sound source with a small recording level such as a CD sound source, the signal-to-noise ratio can be calculated at an appropriate sound source level (S1). In this case, the noise level estimation unit 18 may limit the upper and lower limits of the sound source level (S1) output from the sound source level analysis unit 32 based on the volume sound source level (S2) output from the volume sound source level calculation unit 35, and output the limited sound source level to the signal-to-noise ratio calculation unit 36. Thereby, for example, even when the sound source level (S1) fluctuates rapidly, or when the analog sound source signal contains unnecessary noise, a stable signal-to-noise ratio can be obtained.

[0065] <Fourth Configuration Example> FIG. 5 is a block diagram showing a fourth configuration example of the noise level estimation unit 18 according to the present embodiment.

[0066] The noise level estimation unit 18 according to the fourth configuration example includes a microphone level analysis unit 31, a sound source level analysis unit 32, a sound source removal unit 33, a speed noise level calculation unit 34, a volume sound source level calculation unit 35, a signal-to-noise ratio calculation unit 36, an output selection unit 37, and a noise level limiting unit 43.

[0067] The microphone level analysis unit 31, the sound source level analysis unit 32, the sound source removal unit 33, the speed noise level calculation unit 34, the volume sound source level calculation unit 35, and the signal-to-noise ratio calculation unit 36 perform the same processing as in the first configuration example.

[0068] Based on the speed noise level (N2) output from the speed noise level calculation unit 34, the noise level limiting unit 43 limits the upper and lower limits of the noise level (M - S1) output from the sound source removal unit 33, and outputs the limited noise level as the limited noise level. For example, the noise level limiting unit 43 performs the following processes (D1) to (D3).

[0069] (D1) When the noise level (M - S1) is greater than the level obtained by adding a predetermined value Max2 to the speed noise level (N2), the noise level limiting unit 43 outputs the level obtained by adding the predetermined value Max2 to the speed noise level (N2) as the limited noise level. (D2) When the noise level (M - S1) is less than the level obtained by subtracting a predetermined value Min2 from the speed noise level (N2), the noise level limiting unit 43 outputs the level obtained by subtracting the predetermined value Min2 from the speed noise level (N2) as the limited noise level. (D3) When the noise level (M - S1) does not fall under either of (D1) and (D2) above, the noise level limiting unit 43 outputs the noise level (M - S1) as the limited noise level as it is. That is, when the noise level (M - S1) is less than or equal to the level obtained by adding a predetermined value Max2 to the speed noise level (N2) and greater than or equal to the level obtained by subtracting a predetermined value Min2 from the speed noise level (N2), the noise level limiting unit 43 outputs the noise level (M - S1) as the limited noise level as it is.

[0070] Note that the above limit noise level may be included in the levels related to the noise level. The levels related to the noise level and the speed noise level may be included in the estimated noise level candidates.

[0071] Based on the SN ratio output from the SN ratio calculation unit 36, the output selection unit 37 selects any one of the limit noise level output from the noise level restriction unit 43 and the speed noise level (N2) output from the speed noise level calculation unit 34, and outputs it as the estimated noise level. For example, the output selection unit 37 makes the selections shown in the following (E1) to (E2).

[0072] (E1) When the SN ratio is equal to or less than a predetermined threshold Th2, the output selection unit 37 selects the limit noise level and outputs it as the estimated noise level. (E2) When the SN ratio is greater than a predetermined threshold Th2, the output selection unit 37 selects the speed noise level (N2) and outputs it as the estimated noise level.

[0073] FIG. 6 is a flowchart showing an example of the process performed by the noise level estimation unit 18 having the fourth configuration example.

[0074] The noise level estimation unit 18 calculates the speed noise level (N2) by the following (Equation 1) (S101). N2 = Nv0+(A(v - v0)) …(Equation 1) Here, v0 indicates the reference speed. v indicates the current vehicle speed. Nv0 indicates the reference speed noise level at the reference speed v0. A indicates the change amount of the speed noise level per unit speed.

[0075] The noise level estimation unit 18 calculates the volume sound source level (S2) by the following (Equation 2) (S102). S2 = S0 + vol …(Equation 2) Here, vol indicates the current volume. S0 indicates the sound source level at the position of the microphone when the volume vol is 0.

[0076] The noise level estimation unit 18 calculates the signal-to-noise ratio of the volume sound source level (S2) and the speed noise level (N2) according to the following (Equation 3) (S103). (Signal-to-noise ratio) = S2 - N2 …(Equation 3) Here, in the present embodiment, S2 and N2 are described as being indicated by units using common logarithms. Therefore, the signal-to-noise ratio is calculated by performing the subtraction shown in the above equation. When S2 and N2 are indicated without using common logarithms, the signal-to-noise ratio is calculated by performing the division of S2 and N2.

[0077] The noise level estimation unit 18 determines whether the signal-to-noise ratio > threshold Th2 (S104).

[0078] When the signal-to-noise ratio > threshold Th2 (S104: YES), the noise level estimation unit 18 outputs the speed noise level (N2) as the estimated noise level (S105). Then, the noise level estimation unit 18 ends this process.

[0079] When the signal-to-noise ratio ≤ threshold Th2 (S104: NO), the noise level estimation unit 18 calculates the noise level Nsub according to the following (Equation 4) (S106). Note that Nsub corresponds to the above noise level (M - S1). Nsub = 10log10{10 (M / 10) -10 (S1 / 10)} …(Equation 4) Here, M indicates the microphone level. S1 indicates the sound source level.

[0080] The noise level estimation unit 18 determines whether Nsub > (N2 + Max2) (S107).

[0081] When Nsub > (N2 + Max2) (S107: YES), the noise level estimation unit 18 outputs the restricted noise level (N2 + Max2) as the estimated noise level (S108). Then, the noise level estimation unit 18 ends this process.

[0082] When Nsub ≦ (N2 + Max2) (S107: NO), the noise level estimation unit 18 determines whether Nsub < (N2 - Min2) (S109).

[0083] When Nsub < (N2 - Min2) (S109: YES), the noise level estimation unit 18 outputs the restricted noise level (N2 - Min2) as the estimated noise level (S110). Then, the noise level estimation unit 18 ends this process.

[0084] When Nsub ≧ (N2 - Min2) (S109: NO), the noise level estimation unit 18 outputs the restricted noise level (in this case, the noise level (Nsub)) as the estimated noise level (S111). That is, the original noise level (Nsub) not restricted by the noise level restriction unit 43 is output as the estimated noise level. Then, the noise level estimation unit 18 ends this process.

[0085] Next, with reference to FIGS. 7A, 7B, 7C, and 7D, the error between the actually measured noise level and the estimated noise level with respect to the SN ratio between the sound source level and the noise level will be described.

[0086] FIG. 7A is a graph with the SN ratio calculated using the microphone level as the estimated noise level on the horizontal axis. FIG. 7B is a graph with the SN ratio calculated using the noise level output from the sound source removal unit 33 as the estimated noise level on the horizontal axis. FIG. 7C is a graph with the SN ratio calculated using the microphone level as the estimated noise level when the SN ratio is less than or equal to the threshold Th2, and using the speed noise level as the estimated noise level when the SN ratio is greater than the threshold Th2 on the horizontal axis. FIG. 7D is a graph with the SN ratio calculated using the noise level output from the sound source removal unit 33 as the estimated noise level when the SN ratio is less than or equal to the threshold Th2, and using the speed noise level as the estimated noise level when the SN ratio is greater than the threshold Th2 on the horizontal axis. In the graphs of FIGS. 7A, 7B, 7C, and 7D, the horizontal axis represents the SN ratio [dB], and the vertical axis represents the error [dB] between the actually measured noise level and the estimated noise level.

[0087] When the microphone level is directly used as the estimated noise level, as shown in the graph of Fig. 7A, as the SNR increases, the error between the actually measured noise level and the estimated noise level increases. This is because as the SNR increases, the proportion of the sound source component in the microphone level increases.

[0088] When the noise level output from the sound source removal unit 33 is directly used as the estimated noise level, as shown in the graph of Fig. 7B, there is almost no error at an SNR of 0 dB or less, but at an SNR of 0 dB or more, the error increases as the SNR increases. This is because as the SNR increases, as described above, the simple energy addition between the sound source signal and the noise signal no longer holds.

[0089] When the SNR is less than or equal to the threshold Th2, the microphone level is used as the estimated noise level, and when the SNR is greater than the threshold Th2, the speed noise level is used as the estimated noise level. As shown in the graph of Fig. 7C, compared with Figs. 7A and 7B, for example, in the range where the SNR is greater than 10 dB, the error becomes smaller. However, around an SNR of 10 dB, the error is slightly larger.

[0090] On the other hand, as in the fourth configuration example, when the SNR is less than or equal to the threshold Th2, the noise level output from the sound source removal unit 33 is used as the estimated noise level, and when the SNR is greater than the threshold Th2, the speed noise level is used as the estimated noise level. As shown in the graph of Fig. 7D, compared with Fig. 7C, even when the SNR is around 10 dB, the error becomes sufficiently small. That is, by adopting the fourth configuration example shown in Fig. 5, the noise level estimation unit 18 can output an estimated noise level with a small error with respect to the actually measured noise level in a wide range of SNRs, as shown in Fig. 7D.

[0091] Next, with reference to FIGS. 8A, 8B, and 8C, the effects of providing the noise level limiting unit 43 will be described. FIG. 8A is a graph showing the temporal change of the estimated noise level when no sudden noise is input to the microphone. FIG. 8B is a graph showing the temporal change of the estimated noise level when no noise level limiting unit 43 is provided and sudden noise is input to the microphone. FIG. 8C is a graph showing the temporal change of the estimated noise level when the noise level limiting unit 43 is provided and sudden noise is input to the microphone. In the graphs of FIGS. 8A, 8B, and 8C, the horizontal axis represents time [seconds], and the vertical axis represents the estimated noise level [dB].

[0092] When the noise level limiting unit 43 is not provided, as shown in the graph of FIG. 8B, the sudden noise input to the microphone is directly output as the estimated noise level. In this case, there is a possibility that the noise following equalizer 12 may unnecessarily increase the sound source level based on the compensation amount calculated by the compensation amount calculation unit 20 with reference to the component derived from this sudden noise.

[0093] On the other hand, by providing the noise level limiting unit 43, as shown in the graph of FIG. 8C, the sudden noise input to the microphone is limited by the noise level limiting unit 43. Therefore, it is suppressed that the component of the sudden noise is included in the estimated noise level. As a result, the compensation amount calculation unit 20 can calculate an appropriate compensation amount, so that it is possible to suppress the noise following equalizer 12 from unnecessarily increasing the sound source level.

[0094] <Fifth Configuration Example> FIG. 9 is a block diagram showing a fifth configuration example of the noise level estimation unit 18 according to the present embodiment.

[0095] The noise level estimation unit 18 according to the fifth configuration example includes a microphone level analysis unit 31, a sound source level analysis unit 32, a sound source removal unit 33, a speed noise level calculation unit 34, a volume sound source level calculation unit 35, an SN ratio calculation unit 36, an output selection unit 37, a microphone level limiting unit 42, and a noise level limiting unit 43.

[0096] The microphone level analysis unit 31, the sound source level analysis unit 32, the sound source removal unit 33, the speed noise level calculation unit 34, the volume sound source level calculation unit 35, and the SN ratio calculation unit 36 perform the same processing as in the first configuration example.

[0097] The microphone level limiting unit 42 limits the upper and lower limits of the microphone level (M) output from the microphone level analysis unit 31 based on the speed noise level (N2), and outputs the limited microphone level as the limited microphone level. For example, the microphone level limiting unit 42 limits the microphone level by the processes (B1) to (B3) shown in the third configuration example.

[0098] The noise level limiting unit 43 limits the upper and lower limits of the noise level (M - S1) output from the sound source removal unit 33 based on the speed noise level (N2), and outputs the limited noise level as the limited noise level. For example, the noise level limiting unit 43 limits the noise level by the processes (D1) to (D3) shown in the fourth configuration example.

[0099] The output selection unit 37 selects any one of the limited microphone level output from the microphone level limiting unit 42, the limited noise level output from the noise level limiting unit 43, and the speed noise level output from the speed noise level calculation unit 34 based on the SN ratio output from the SN ratio calculation unit 36, and outputs it as the estimated noise level. For example, the output selection unit 37 makes the selections shown in the following (F1) to (F3).

[0100] (F1) When the SN ratio is smaller than a predetermined threshold Th0, the output selection unit 37 selects the limited microphone level and outputs it as the estimated noise level. (F2) When the SN ratio is larger than a predetermined threshold Th1, the output selection unit 37 selects the speed noise level (N2) and outputs it as the estimated noise level. Note that the threshold Th1 is larger than the threshold Th0. (F3) The output selection unit 37 selects the restricted noise level and outputs it as the estimated noise level when the SNR does not meet either of the above (F1) and (F2). That is, when the SNR is equal to or greater than the threshold Th0 and equal to or less than the threshold Th1, the output selection unit 37 selects the restricted noise level and outputs it as the estimated noise level.

[0101] Note that the above restricted microphone level may be included in the level related to the microphone level. The above restricted noise level may be included in the level related to the noise level. The level related to the microphone level, the level related to the noise level, and the speed noise level may be included in the estimated noise level candidates.

[0102] By providing the microphone level limiting unit 42, sudden noise input to the microphone is limited by the microphone level limiting unit 42. Therefore, it is suppressed that the component of sudden noise is included in the restricted microphone level. As a result, even when sudden noise is included in the microphone level, since the restricted microphone level is output as the estimated noise level, the compensation amount calculation unit 20 can calculate an appropriate compensation amount.

[0103] Also, by providing the noise level limiting unit 43, similar to the case of the fourth configuration example, even when sudden noise is included in the microphone level, since the restricted noise level is output as the estimated noise level, the compensation amount calculation unit 20 can calculate an appropriate compensation amount.

[0104] Therefore, according to the fifth configuration example, the noise follow-up equalizer 12 can be suppressed from unnecessarily increasing the sound source level.

[0105] FIG. 10 is a flowchart showing an example of the process performed by the noise level estimation unit 18 having the fifth configuration example.

[0106] The noise level estimation unit 18 calculates the speed noise level (N2) according to the following (Equation 1) (S201). N2 = Nv0+(A(v - v0)) …(Equation 1)

[0107] The noise level estimation unit 18 calculates the volume sound source level (S2) according to the following (Equation 2) (S202). S2 = S0 + vol …(Equation 2)

[0108] The noise level estimation unit 18 calculates the signal-to-noise ratio between the volume sound source level (S2) and the speed noise level (N2) according to the following (Equation 3) (S203). (Signal-to-noise ratio) = S2 - N2 …(Equation 3)

[0109] The noise level estimation unit 18 determines whether the signal-to-noise ratio is less than the threshold Th0 (S204).

[0110] When the signal-to-noise ratio ≧ the threshold Th0 (S204: NO), the noise level estimation unit 18 executes a sub-process (S300) and ends this process. The details of the sub-process will be described later (see FIG. 11).

[0111] When the signal-to-noise ratio < the threshold Th0 (S204: YES), the noise level estimation unit 18 determines whether M > (N2 + Max1) (S205).

[0112] When M > (N2 + Max1) (S205: YES), the noise level estimation unit 18 outputs the limited microphone level (N2 + Max1) as the estimated noise level (S206). That is, the noise level estimation unit 18 outputs the limited microphone level limited to the upper limit (N2 + Max1) by the microphone level limiting unit 42 as the noise estimated level. Then, the noise level estimation unit 18 ends this process.

[0113] When M ≧ (N2 + Max1) (S205: NO), the noise level estimation unit 18 determines whether M < (N2 - Min1) (S207).

[0114] When M < (N2 - Min1) (S207: YES), the noise level estimation unit 18 outputs the restricted microphone level (N2 - Min1) as the estimated noise level (S208). That is, the noise level estimation unit 18 outputs the restricted microphone level restricted to the lower limit (N2 - Min1) by the microphone level restriction unit 42 as the estimated noise level. Then, the noise level estimation unit 18 ends this process.

[0115] When M ≥ (N2 - Min1) (S207: NO), the noise level estimation unit 18 outputs the restricted microphone level (in this case, the microphone level (M)) as the estimated noise level (S209). That is, the noise level estimation unit 18 outputs the original microphone level (M) not restricted by the microphone level restriction unit 42 as the estimated noise level. Then, the noise level estimation unit 18 ends this process.

[0116] FIG. 11 is a flowchart showing an example of the sub - process (S300) shown in FIG. 10.

[0117] The noise level estimation unit 18 determines whether the SNR > threshold Th1 (S301).

[0118] When the SNR > threshold Th1 (S301: YES), the noise level estimation unit 18 outputs the speed noise level (N2) as the estimated noise level (S302). Then, the noise level estimation unit 18 returns to the process after step S300 in FIG. 10.

[0119] When the SNR ≤ threshold Th1 (S301: NO), the noise level estimation unit 18 calculates the noise level Nsub by the following (Equation 4) (S303). Nsub = 10 log10 {10 (M / 10) - 10 (S1 / 10)} …(Equation 4)

[0120] The noise level estimation unit 18 determines whether Nsub > (N2 + Max2) (S304).

[0121] When Nsub > (N2 + Max2) (S304: YES), the noise level estimation unit 18 outputs the restricted noise level (N2 + Max2) as the estimated noise level (S305). That is, the noise level estimation unit 18 outputs the restricted noise level restricted to the upper limit (N2 + Max2) by the noise level restriction unit 43 as the estimated noise level. Then, the noise level estimation unit 18 returns to the process after step S300 in FIG. 10.

[0122] When Nsub ≤ (N2 + Max2) (S304: NO), the noise level estimation unit 18 determines whether Nsub < (N2 - Min2) (S306).

[0123] When Nsub < (N2 - Min2) (S306: YES), the noise level estimation unit 18 outputs the restricted noise level (N2 - Min2) as the estimated noise level (S308). That is, the noise level estimation unit 18 outputs the restricted noise level restricted to the lower limit (N2 - Min2) by the noise level restriction unit 43 as the estimated noise level. Then, the noise level estimation unit 18 returns to the process after step S300 in FIG. 10.

[0124] When Nsub ≥ (N2 - Min2) (S306: NO), the noise level estimation unit 18 outputs the restricted noise level (in this case, the noise level (Nsub)) as the estimated noise level (S308). That is, the noise level estimation unit 18 outputs the original noise level not restricted by the noise level restriction unit 43 as the estimated noise level. Then, the noise level estimation unit 18 returns to the process after step S300 in FIG. 10.

[0125] (Summary of the present disclosure) The content of the present disclosure can be expressed as follows in the following supplementary note.

[0126] <Supplementary Note 1> The acoustic processing device 10 mounted on the vehicle of the present disclosure includes a sound source removal unit 33, a speed noise level calculation unit 34, a volume sound source level calculation unit 35, an SN ratio calculation unit 36, and an output selection unit 37. The sound source removal unit 33 outputs a noise level obtained by subtracting the sound source level from the microphone level. The microphone level indicates the frequency characteristics of a microphone signal collected by a microphone provided inside the vehicle. The sound source level indicates the frequency characteristics of a sound source signal output from a speaker provided inside the vehicle. The speed noise level calculation unit 34 outputs a speed noise level indicating the frequency characteristics of noise based on the speed of the vehicle. The volume sound source level calculation unit 35 outputs a volume sound source level indicating the frequency characteristics based on the volume of a predetermined sound source signal. The SN ratio calculation unit 36 outputs an SN ratio that is the ratio between the volume sound source level and the speed noise level. The output selection unit 37 selects, based on the SN ratio, any one of the level related to the noise level and the candidate estimated noise levels including the speed noise level, and outputs it as the estimated noise level. Thereby, even when the SN ratio changes, the acoustic processing device 10 can output an estimated noise level with a small error from the noise level actually measured inside the vehicle. Therefore, the acoustic processing device 10 can calculate a compensation amount using the estimated noise level, and adjust the sound source level using the compensation amount, thereby outputting sound with an appropriate volume and sound quality in terms of auditory sensation.

[0127] <Appendix 2> In the acoustic processing device 10 described in Appendix 1, when the SN ratio is greater than the first threshold, the output selection unit 37 selects the speed noise level. Thereby, the acoustic processing device 10 can output an estimated noise level with a smaller error from the noise level actually measured inside the vehicle when the SN ratio is greater than the first threshold and when it is equal to or less than the first threshold, respectively.

[0128] <Appendix 3> The acoustic processing device 10 described in Appendix 1 or 2 further includes a noise level limiting unit 43 that limits the noise level based on the speed noise level. The level related to the noise level in the output selection unit 37 is the noise level limited by the noise level limiting unit 43. This suppresses the inclusion of sudden noise in the estimated noise level. Therefore, when adjusting the sound source level using the compensation amount, the acoustic processing device 10 can suppress unnecessarily adjusting the sound source level.

[0129] <Appendix 4> In the acoustic processing device 10 described in Appendix 1, the estimated noise level candidate further includes a level related to the microphone level, and the output selection unit 37 selects any one of the level related to the microphone level, the level related to the noise level, and the speed noise level based on the SNR and outputs it as the estimated noise level. Thereby, even when the SNR changes, the acoustic processing device 10 can output an estimated noise level with a small error from the noise level actually measured inside the vehicle.

[0130] <Appendix 5> In the acoustic processing device 10 described in Appendix 4, when the SNR is smaller than the first threshold, the output selection unit 37 selects the level related to the microphone level, and when the SNR is larger than the second threshold larger than the first threshold, the output selection unit 37 selects the speed noise level. When the SNR is equal to or greater than the first threshold and equal to or less than the second threshold, the output selection unit 37 selects the level related to the noise level. Thereby, when the SNR is smaller than the first threshold, larger than the second threshold, and other cases, the acoustic processing device 10 can output an estimated noise level with a smaller error from the noise level actually measured inside the vehicle, respectively.

[0131] <Appendix 6> The acoustic processing device 10 described in Appendix 4 or 5 further includes a microphone level limiting unit 42 that limits the microphone level based on the speed noise level. The level related to the microphone level in the output selection unit 37 is the microphone level limited by the microphone level limiting unit 42. This suppresses the inclusion of sudden noise in the estimated noise level. Therefore, when adjusting the sound source level using the compensation amount, the acoustic processing device 10 can suppress unnecessarily adjusting the sound source level.

[0132] <Appendix 7> The acoustic processing apparatus 10 according to any one of Appendices 4 to 6 further includes a noise level limiting unit 43 that limits the noise level based on the speed noise level. The level regarding the noise level in the output selection unit 37 is the noise level limited by the noise level limiting unit 43. This suppresses the inclusion of sudden noise in the estimated noise level. Therefore, when adjusting the sound source level using the compensation amount, the acoustic processing apparatus 10 can suppress unnecessarily adjusting the sound source level.

[0133] <Appendix 8> The acoustic processing apparatus 10 mounted on the vehicle of the present disclosure includes a sound source removal unit 33, a speed noise level calculation unit 34, a volume sound source level calculation unit 35, a microphone level limiting unit 42, a signal-to-noise ratio calculation unit 36, and an output selection unit 37. The sound source removal unit 33 outputs a noise level obtained by subtracting the sound source level from the microphone level. The microphone level indicates the frequency characteristics of the microphone signal collected by a microphone provided inside the vehicle. The sound source level indicates the frequency characteristics of the sound source signal output from a speaker provided inside the vehicle. The speed noise level calculation unit 34 outputs a speed noise level indicating the frequency characteristics of the noise based on the speed of the vehicle. The volume sound source level calculation unit 35 outputs a volume sound source level indicating the frequency characteristics based on the volume of a predetermined sound source signal. The microphone level limiting unit 42 outputs a limited microphone level, which is the microphone level limited based on the speed noise level. The signal-to-noise ratio calculation unit 36 outputs a signal-to-noise ratio that is the ratio of the volume sound source level to the limited microphone level. The output selection unit 37 selects any one of the microphone level, the noise level, and the limited microphone level based on the signal-to-noise ratio and outputs it as the estimated noise level. As a result, even when the signal-to-noise ratio changes, the acoustic processing device 10 can output an estimated noise level with a small error from the noise level actually measured inside the vehicle. Therefore, the acoustic processing device 10 can calculate a compensation amount using the estimated noise level, and by adjusting the sound source level using the compensation amount, can output sound with an appropriate volume and sound quality in terms of auditory sensation.

[0134] <Appendix 9> The acoustic processing device 10 mounted on the vehicle of the present disclosure includes a sound source removal unit 33, a speed noise level calculation unit 34, a volume sound source level calculation unit 35, a signal-to-noise ratio calculation unit 36, and an output selection unit 37. The sound source removal unit 33 outputs a noise signal obtained by subtracting a sound source signal using an adaptive filter from a microphone signal collected by a microphone provided inside the vehicle. The sound source signal is output from a speaker provided inside the vehicle. The speed noise level calculation unit 34 outputs a speed noise level indicating the frequency characteristics of the noise based on the speed of the vehicle. The volume sound source level calculation unit 35 outputs a volume sound source level indicating the frequency characteristics based on the volume of a predetermined sound source signal. The signal-to-noise ratio calculation unit 36 outputs a signal-to-noise ratio that is the ratio of the volume sound source level to the speed noise level. The output selection unit 37 selects any one of a microphone level indicating the frequency characteristics of the microphone signal, a noise level indicating the frequency characteristics of the noise signal, and the speed noise level based on the signal-to-noise ratio, and outputs it as the estimated noise level. As a result, even when the signal-to-noise ratio changes, the acoustic processing device 10 can output an estimated noise level with a small error from the noise level actually measured inside the vehicle. Therefore, the acoustic processing device 10 can calculate a compensation amount using the estimated noise level, and by adjusting the sound source level using the compensation amount, can output sound with an appropriate volume and sound quality in terms of auditory sensation.

[0135] <Appendix 10> The acoustic processing method by the device mounted on the vehicle of the present disclosure includes the following processes 1 to 5. In Process 1, a noise level obtained by subtracting the sound source level from the microphone level is output. The microphone level indicates the frequency characteristics of a microphone signal collected by a microphone provided inside the vehicle. The sound source level indicates the frequency characteristics of a sound source signal output from a speaker provided inside the vehicle. In Process 2, a speed noise level indicating the frequency characteristics of noise based on the vehicle speed is output. In Process 3, a volume sound source level indicating the frequency characteristics based on the volume of a predetermined sound source signal is output. In Process 4, a signal-to-noise ratio (SN ratio), which is the ratio of the volume sound source level to the speed noise level, is output. In Process 5, based on the SN ratio, one of the level related to the noise level and the speed noise level is selected and output as an estimated noise level. With this acoustic processing method, even when the SN ratio changes, an estimated noise level with a small error from the actually measured noise level inside the vehicle can be output. Therefore, a device to which this acoustic processing method is applied can calculate a compensation amount using the estimated noise level, and adjust the sound source level using the compensation amount, thereby outputting sound with an appropriate volume and sound quality in terms of auditory sensation.

[0136] As described above, the embodiments have been explained with reference to the accompanying drawings, but the present disclosure is not limited to such examples. It is obvious that those skilled in the art can conceive various modification examples, correction examples, substitution examples, addition examples, deletion examples, equivalent examples within the scope described in the claims, and it is understood that they also belong to the technical scope of the present disclosure. Also, within the scope not departing from the gist of the invention, the components in the above-described embodiments may be arbitrarily combined.

Industrial Applicability

[0137] The technology of the present disclosure can be used in an acoustic device mounted on a vehicle.

Explanation of Reference Numerals

[0138] 10 Acoustic Processing Device 11 Sound Source Signal Input Unit 12 Noise-Following Equalizer 13 Volume amplification unit 14 Speaker 15 Microphone signal input unit 16 Speed input unit 17 Volume input unit 18 Noise level estimation unit 19 Sound source level analysis unit 20 Compensation amount calculation unit 31 Microphone level analysis unit 32 Sound source level analysis unit 33 Sound source removal unit 34 Speed noise level calculation unit 35 Volume sound source level calculation unit 36 SNR calculation unit 37 Output selection unit 38 Subtraction processing unit 39 Noise level analysis unit 40 Adaptive filter unit 41 LMS algorithm unit 42 Microphone level limitation unit 43 Noise level limitation unit

Claims

1. An acoustic processing device mounted on a vehicle, comprising: a sound source removal unit that outputs a noise level obtained by subtracting a sound source level from a microphone level; a speed noise level calculation unit that outputs a speed noise level indicating a frequency characteristic of noise based on the speed of the vehicle; a volume sound source level calculation unit that outputs a volume sound source level indicating a frequency characteristic based on the volume of a predetermined sound source signal; an SN ratio calculation unit that outputs an SN ratio which is a ratio between the volume sound source level and the speed noise level; an output selection unit that selects any one of a level related to the noise level and an estimated noise level candidate including the speed noise level based on the SN ratio, and outputs the selected level as an estimated noise level; a noise level limitation unit that limits the noise level based on the speed noise level; wherein the microphone level indicates a frequency characteristic of a microphone signal collected by a microphone provided inside the vehicle; the sound source level indicates a frequency characteristic of a sound source signal output from a speaker provided inside the vehicle; the output selection unit selects the speed noise level when the SN ratio is greater than a first threshold; the level related to the noise level in the output selection unit is the noise level limited by the noise level limitation unit; an acoustic processing device.

2. An acoustic processing device mounted on a vehicle, comprising: a sound source removal unit that outputs a noise level obtained by subtracting a sound source level from a microphone level; a speed noise level calculation unit that outputs a speed noise level indicating a frequency characteristic of noise based on the speed of the vehicle; a volume sound source level calculation unit that outputs a volume sound source level indicating a frequency characteristic based on the volume of a predetermined sound source signal; an SN ratio calculation unit that outputs an SN ratio which is a ratio between the volume sound source level and the speed noise level; an output selection unit that selects any one of a level related to the microphone level, a level related to the noise level, and an estimated noise level candidate including the speed noise level based on the SN ratio, and outputs the selected level as an estimated noise level; a microphone level limitation unit that limits the microphone level based on the speed noise level; wherein the microphone level indicates a frequency characteristic of a microphone signal collected by a microphone provided inside the vehicle; the sound source level indicates a frequency characteristic of a sound source signal output from a speaker provided inside the vehicle; the output selection unit selects the level related to the microphone level when the SN ratio is less than a first threshold; When the SNR is greater than a second threshold that is greater than the first threshold, select the speed noise level, When the SNR is greater than or equal to the first threshold and less than or equal to the second threshold, select the level related to the noise level, The level related to the microphone level in the output selection unit is the microphone level restricted by the microphone level restriction unit, Acoustic processing device.

3. An acoustic processing device mounted on a vehicle, A sound source removal unit that outputs a noise level obtained by subtracting a sound source level from a microphone level; A speed noise level calculation unit that outputs a speed noise level indicating the frequency characteristics of noise based on the speed of the vehicle; A volume sound source level calculation unit that outputs a volume sound source level indicating the frequency characteristics based on the volume of a predetermined sound source signal; An SNR calculation unit that outputs an SNR that is the ratio of the volume sound source level to the speed noise level; Based on the SNR, select any one of the estimated noise level candidates including the level related to the microphone level, the level related to the noise level, and the speed noise level, and output it as the estimated noise level; An output selection unit; A noise level restriction unit that restricts the noise level based on the speed noise level, The microphone level indicates the frequency characteristics of a microphone signal collected by a microphone provided inside the vehicle, The sound source level indicates the frequency characteristics of a sound source signal output from a speaker provided inside the vehicle, The output selection unit, When the SNR is less than the first threshold, select the level related to the microphone level, When the SNR is greater than a second threshold that is greater than the first threshold, select the speed noise level, When the SNR is greater than or equal to the first threshold and less than or equal to the second threshold, select the level related to the noise level, The level related to the noise level in the output selection unit is the noise level restricted by the noise level restriction unit, Acoustic processing device.

4. An acoustic processing device mounted on a vehicle, A sound source removal unit that outputs a noise level obtained by subtracting a sound source level from a microphone level; A speed noise level calculation unit that outputs a speed noise level indicating the frequency characteristics of noise based on the speed of the vehicle; A volume sound source level calculation unit that outputs a volume sound source level indicating the frequency characteristics based on the volume of a predetermined sound source signal; A microphone level limiting unit that outputs a limited microphone level, which is the microphone level limited based on the speed noise level; An SN ratio calculation unit that outputs an SN ratio, which is a ratio between the volume sound source level and the limited microphone level; An output selection unit that selects any one of the microphone level, the noise level, and the limited microphone level based on the SN ratio and outputs it as an estimated noise level, The microphone level indicates the frequency characteristics of a microphone signal collected by a microphone provided inside the vehicle; The sound source level indicates the frequency characteristics of a sound source signal output from a speaker provided inside the vehicle; The output selection unit selects the level related to the microphone level when the SN ratio is smaller than a first threshold; selects the limited microphone level when the SN ratio is larger than a second threshold that is larger than the first threshold; selects the level related to the noise level when the SN ratio is equal to or greater than the first threshold and equal to or less than the second threshold. An acoustic processing device.

5. An acoustic processing method by a device mounted on a vehicle, outputs a noise level obtained by subtracting a sound source level from a microphone level, outputs a speed noise level indicating the frequency characteristics of noise based on the speed of the vehicle, outputs a volume sound source level indicating the frequency characteristics based on the volume of a predetermined sound source signal, outputs an SN ratio, which is a ratio between the volume sound source level and the speed noise level, selects any one of the level related to the noise level and the speed noise level based on the SN ratio and outputs it as an estimated noise level, The microphone level indicates the frequency characteristics of a microphone signal collected by a microphone provided inside the vehicle; The sound source level indicates the frequency characteristics of a sound source signal output from a speaker provided inside the vehicle; selects the speed noise level when the SN ratio is larger than a first threshold; The level related to the noise level is the noise level limited based on the speed noise level, An acoustic processing method.

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