JP6143554B2 - Active noise control device - Google Patents

Description

  The present invention relates to an active noise control device (hereinafter referred to as ANC) that actively reduces road noise in a vehicle cabin and noise caused by engine operation, for example.

  For example, Patent Document 1 discloses an ANC that actively reduces noise in a vehicle cabin. In this ANC, the amplitude of the control signal for canceling the vehicle interior noise is adjusted according to the vehicle speed and / or the size of the audio signal, so that the audio signal is exclusively canceled from the output of the sound signal collected by the microphone. A circuit is unnecessary, and the influence on the musical tone can be reduced.

JP 2008-137636 A

In the conventional technique represented by Patent Document 1, it is necessary to input into the ANC a factor that may change the transfer function in the vehicle interior such as the vehicle speed.
However, in an actual vehicle interior environment, all factors that change the vehicle interior transfer function cannot be detected by the vehicle-side system. For example, when an occupant places a bag or the like that can be a sound absorbing material in front of a speaker, the environment between the speaker and the microphone may change significantly.
In this case, the system on the vehicle side cannot detect this change, and there is a problem that the ANC does not operate normally.
In other words, since the vehicle interior noise cannot be correctly detected by the microphone, the noise anti-phase signal cannot be maintained and the noise reduction operation becomes unstable, which may increase the noise.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an active noise control apparatus that can stably perform noise reduction operation in a target space.

The active noise control device according to the present invention generates a control signal for reducing noise detected by the sound detection unit, and outputs the control signal from the sound output unit as a sound wave to be reduced by interfering with the noise. In addition, the sound signal detected by the sound detection unit is input and the sound signal to be output from the sound output unit is branched and input, and the active noise control operating frequency in the frequency band of the reference transfer function based on these sound signals continuous a transfer function calculating unit that calculates a transfer function of the frequency band other than the band, a condition that the difference between the transfer function and the transfer function calculating unit reference transfer function is calculated in the object space to reduce the noise is equal to or more than a predetermined range a transfer function comparing section for outputting a trigger signal when to filled, ANC controller to stop the active noise control when receiving a trigger signal output from the transfer function comparing unit Characterized by comprising a.

  According to the present invention, there is an effect that the noise reduction operation in the target space can be stably performed.

It is a block diagram which shows the structure of the audio apparatus to which the active noise control apparatus which concerns on Embodiment 1 of this invention is applied. 3 is a flowchart showing an operation of the active noise control apparatus according to the first embodiment.

Embodiment 1 FIG.
1 is a block diagram showing the configuration of an audio apparatus to which an active noise control apparatus according to Embodiment 1 of the present invention is applied. The audio device shown in FIG. 1 is an audio device that outputs an audio signal input by a DSP (Digital Signal Processor) 2 as sound waves from a speaker 5, and includes an ANC 1, a DSP 2, a synthesis circuit 3, an amplifier circuit 4, a speaker 5, and a microphone 6. It is configured with.
The ANC 1 is an ANC that performs active noise control using a region between the speaker 5 and the microphone 6 as a noise reduction target space, and includes an ANC control unit 10, a transfer function calculation unit 11, and a transfer function comparison unit 12. Configured.

Here, normal active noise control will be described.
The ANC control unit 10 acquires engine or electric motor rotation speed information from the vehicle side via a CAN (Controller Area Network) bus or signal line input, and this rotation speed from the microphone input signal detected by the microphone 6. The frequency component of booming noise proportional to is detected. Next, the ANC control unit 10 generates an ANC signal that is a control signal for controlling the detected noise so as to have an opposite phase around the microphone 6 and outputs the ANC signal to the synthesis circuit 3. The frequency band for performing active noise control is a frequency band of 20 to 300 Hz including the above-described noise frequency component.

  The synthesizing circuit 3 synthesizes the ANC signal with the audio signal input from the DSP 2 and outputs it to the amplifier circuit 4. The amplifier circuit 4 amplifies the audio signal combined with the ANC signal to a predetermined sound pressure level and outputs it to the speaker 5. The speaker 5 outputs the audio signal as a noise canceling sound. Thereby, the noise in the area | region between the speaker 5 and the microphone 6 is reduced.

The ANC control unit 10 calculates the gain characteristic and phase characteristic from the output end of the ANC control unit 10 to the input end of the ANC control unit 10 through the region between the speaker 5 and the microphone 6, that is, the transfer function. Know and hold in advance.
Thereby, the ANC control unit 10 can generate a noise (cancellation sound) having a noise level at the position of the microphone 6 and having a phase opposite to that of the noise as an ANC signal.
The transfer function is called a reference transfer function because it does not change if the environment in the vehicle compartment is constant. For example, a gain characteristic and a phase characteristic in a frequency band of 20 to 5 kHz are set as a reference transfer function.

Next, operations unique to the ANC 1 according to the present invention will be described.
FIG. 2 is a flowchart showing the operation of the active noise control apparatus according to the first embodiment.
When ANC1 starts active noise control (step ST1), first, the transfer function comparison unit 12 initializes parameters M and N to 0 (step ST2).
Subsequently, the transfer function calculation unit 11 periodically inputs the sound signal detected by the microphone 6 (every second) (step ST3), and outputs the audio signal output from the DSP 2 for output from the speaker 5. Is branched and input as a feedback signal.

  Thereafter, the transfer function calculation unit 11 calculates a transfer function in a frequency band outside the operating frequency band of the active noise control in the frequency band of the reference transfer function based on these input signals (step ST4). Thereby, a so-called partial transfer function corresponding to the frequency band of the reference transfer function is calculated.

Here, the gain characteristic is calculated as a transfer function. When the frequency band of the reference transfer function is 20 to 5 kHz and the operating frequency band of the active noise control is 20 to 300 Hz, for example, the frequency band of 500 Hz to 5 kHz. The gain characteristic I at is calculated.
In the active frequency band of active noise control, the ANC 1 operates so as to reduce the surrounding sound of the microphone 6, so that the feedback signal and the output signal of the speaker 5 are not equal, and an accurate transfer function cannot be calculated. For this reason, the transfer function in the frequency band outside the operating frequency band of the active noise control in the frequency band of the reference transfer function is calculated.

The transfer function comparison unit 12 determines whether or not the absolute value of the difference obtained by subtracting the gain characteristic of the reference transfer function from the gain characteristic I calculated by the transfer function calculation unit 11 is greater than or equal to a predetermined range (step ST5). Here, it is determined whether or not the absolute value of the difference between the gain characteristic I and the gain characteristic of the reference transfer function is, for example, 5 dB or more.
When the absolute value of the difference between the gain characteristic I and the gain characteristic of the reference transfer function is 5 dB or more (step ST5; YES), the transfer function comparison unit 12 sets parameter M to 0 and increments parameter N by +1 (step ST5). ST6).

Next, the transfer function comparison unit 12 determines whether or not the parameter N has become 5, that is, whether or not the absolute value of the difference between the gain characteristic I and the gain characteristic of the reference transfer function has been 5 dB or more continuously 5 times. Determination is made (step ST7). Note that the condition of 5 times is an example, and the user may set as appropriate, or the predetermined number of times may be fixedly set.
Thus, it is determined whether or not the condition that the absolute value of the difference between the gain characteristic I and the gain characteristic of the reference transfer function is 5 dB or more continuously is satisfied.

  When the parameter N becomes 5 (step ST7; YES), the transfer function comparison unit 12 generates a trigger signal indicating that the characteristic in the vehicle interior has changed and outputs the trigger signal to the ANC control unit 10. The ANC control unit 10 stops the active noise control when receiving the trigger signal output from the transfer function comparison unit 12 (step ST8). Then, it returns to step ST2 and repeats the process mentioned above.

If the parameter N is not 5 (step ST7; NO), the ANC 1 waits for 1 second (step ST9) and returns to the process of step ST3.
When the absolute value of the difference between the gain characteristic I and the gain characteristic of the reference transfer function is less than 5 dB (step ST5; NO), the transfer function comparison unit 12 sets the parameter N to 0 and increments the parameter M by +1. (Step ST10).
Next, the transfer function comparison unit 12 determines whether or not the parameter M has become 5, that is, whether or not the absolute value of the difference between the gain characteristic I and the gain characteristic of the reference transfer function has been less than 5 dB for five consecutive times. Determine (step ST11). Note that the condition of 5 times is an example, and the user may set as appropriate, or the predetermined number of times may be fixedly set.

When the parameter M becomes 5 (step ST11; YES), the transfer function comparison unit 12 generates a signal indicating that the vehicle interior characteristics have not changed and outputs the signal to the ANC control unit 10. Upon receiving the signal output from the transfer function comparison unit 12, the ANC control unit 10 returns to step ST1 and resumes active noise control. Thereafter, the above-described processing is repeated.
On the other hand, when the parameter M is not 5 (step ST11; NO), the ANC 1 waits for 1 second (step ST12) and returns to the process of step ST3.
The transfer function calculation unit 11 continuously calculates the transfer function even after the active noise control is stopped, and when it is detected that the vehicle interior characteristics have returned to the reference transfer function, the transfer function comparison unit 12 Cancels the output of the trigger signal to the ANC control unit 10, and the ANC 1 returns to the normal active noise control operation.

As described above, according to the first embodiment, the sound signal detected by the microphone 6 is input, the sound signal to be output from the speaker 5 is branched and input, and the reference transfer function is based on these sound signals. A transfer function calculation unit 11 that calculates a transfer function in a frequency band other than the operating frequency band of the active noise control in the frequency band, a reference transfer function in a target space for reducing noise, and a transfer function calculated by the transfer function calculation unit 11 A transfer function comparison unit 12 that outputs a trigger signal when a condition that the difference between the two is equal to or greater than a predetermined range is satisfied, and an ANC that stops active noise control when a trigger signal output from the transfer function comparison unit 12 is received And a control unit 10.
For example, when the gain characteristic in the passenger compartment changes, the ANC signal cannot be calculated accurately, and noise may be diffused. Therefore, the active noise control is stopped when a change in the gain characteristic in the vehicle interior is detected while satisfying the above conditions.
With this configuration, it is possible to stably perform the noise reduction operation in the target space where noise is reduced (the region between the speaker 5 and the microphone 6).

  In the present invention, any component of the embodiment can be modified or any component of the embodiment can be omitted within the scope of the invention.

  1 ANC device, 2 DSP, 3 synthesis circuit, 4 amplifier circuit, 5 speaker, 6 microphone, 10 ANC control unit, 11 transfer function calculation unit, 12 transfer function comparison unit.

Claims (1)

In the active noise control device that generates a control signal for reducing the noise detected by the sound detection unit, and outputs the control signal from the sound output unit as a sound wave to be reduced by interfering with the noise,
The sound signal detected by the sound detection unit is input and the sound signal to be output from the sound output unit is branched and input, and the active noise control operating frequency in the frequency band of the reference transfer function based on these sound signals A transfer function calculator that calculates a transfer function in a frequency band other than the band;
Transfer function comparison that outputs a trigger signal when the difference between the reference transfer function and the transfer function calculated by the transfer function calculation unit in the target space for reducing the noise continuously satisfies a predetermined range or more And
An active noise control apparatus comprising: an ANC control unit that stops active noise control when receiving a trigger signal output from the transfer function comparison unit.

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