Active noise reduction device, vehicle, and active noise reduction method

1. An active noise reduction device that reduces noise in a space in a vehicle, the active noise reduction device comprising:

a first reference signal input that receives a first reference signal outputted by a first reference signal source and having a correlation with the noise, the first reference signal source being attached to the vehicle;

a first compressor that compresses and outputs the first reference signal received by the first reference signal input, as a compressed first reference signal, the compressed first reference signal having an amplitude greater than or equal to a first threshold;

an adaptive filter unit that applies an adaptive filter to the compressed first reference signal to generate a canceling signal to be used to output a canceling sound for reducing the noise;

a canceling signal output that receives the canceling signal generated by the adaptive filter unit;

a filter coefficient updater that updates a coefficient of the adaptive filter using at least a step size parameter;

a μ adjuster that adjusts the step size parameter using the first reference signal before being inputted to the first compressor;

an error signal input that receives an error signal corresponding to a residual sound resulting from interference between the canceling sound and the noise;

a second compressor that compresses and outputs the error signal received by the error signal input, as a compressed error signal, the compressed error signal having an amplitude greater than or equal to a second threshold; and

a simulated acoustic transfer characteristics filter unit that generates a filtered reference signal by correcting at least one of the first reference signal and the compressed first reference signal using simulated transfer characteristics that simulate acoustic transfer characteristics from the canceling signal,

wherein the filter coefficient updater updates the coefficient of the adaptive filter using the step size parameter, the compressed error signal outputted from the second compressor, and the filtered reference signal.

2. The active noise reduction device according to claim 1 , further comprising:

a second reference signal input that receives a second reference signal outputted by a second reference signal source and having a correlation with the noise, the second reference signal source being attached to the vehicle; and

a third compressor that compresses and outputs the second reference signal received by the second reference signal input, as a compressed second reference signal, the compressed second reference signal having an amplitude greater than or equal to a third threshold,

wherein the first compressor compresses the first reference signal at a same compression ratio as the third compressor, and

the third compressor compresses the second reference signal having the amplitude less than the third threshold at the same compression ratio as the first compressor.

3. The active noise reduction device according to claim 1 , further comprising:

a second reference signal input that receives a second reference signal outputted by a second reference signal source and having a correlation with the noise, the second reference signal source being attached to the vehicle; and

a third compressor that compresses and outputs the second reference signal received by the second reference signal input, as a compressed second reference signal, the compressed second reference signal having an amplitude greater than or equal to a third threshold,

wherein when the first reference signal is to be compressed at a first compression ratio and the second reference signal is to be compressed at a second compression ratio, compression ratios of the first compressor and the third compressor are each same as a higher one of the first compression ratio and the second compression ratio.

4. The active noise reduction device according to claim 1 ,

wherein the first compressor compresses the first reference signal at a same compression ratio as the second compressor, and

the second compressor compresses the error signal having the amplitude less than the second threshold at the same compression ratio as the first compressor.

5. The active noise reduction device according to claim 1 ,

wherein when the first reference signal is to be compressed at a first compression ratio and the error signal is to be compressed at a second compression ratio, compression ratios of the first compressor and the second compressor are each same as a higher one of the first compression ratio and the second compression ratio.

6. An active noise reduction device that reduces noise in a space in a vehicle, the active noise reduction device comprising:

a first reference signal input that receives a first reference signal outputted by a first reference signal source and having a correlation with the noise, the first reference signal source being attached to the vehicle;

a first compressor that compresses and outputs the first reference signal received by the first reference signal input, as a compressed first reference signal, the compressed first reference signal having an amplitude greater than or equal to a first threshold;

an adaptive filter unit that applies an adaptive filter to the compressed first reference signal to generate a canceling signal to be used to output a canceling sound for reducing the noise;

a canceling signal output that receives the canceling signal generated by the adaptive filter unit;

a filter coefficient updater that updates a coefficient of the adaptive filter using at least a step size parameter;

a μ adjuster that adjusts the step size parameter using the first reference signal before being inputted to the first compressor;

an error signal input that receives an error signal corresponding to a residual sound resulting from interference between the canceling sound and the noise;

a second compressor that compresses and outputs the error signal received by the error signal input at a same compression ratio as the first compressor regardless of an amplitude of the error signal, while the first compressor compresses the first reference signal; and

a simulated acoustic transfer characteristics filter unit that generates a filtered reference signal by correcting at least one of the first reference signal and the compressed first reference signal using simulated transfer characteristics that simulate acoustic transfer characteristics from the canceling signal output to the error signal input,

wherein the filter coefficient updater updates the coefficient of the adaptive filter using the step size parameter, the error signal outputted from the second compressor, and the filtered reference signal.

7. The active noise reduction device according to claim 1 ,

wherein the simulated acoustic transfer characteristics filter unit corrects the first reference signal received by the first reference signal input and before being inputted to the first compressor, using the simulated transfer characteristics.

8. The active noise reduction device according to claim 1 ,

wherein the μ adjuster sets the step size parameter to a value proportional to a reciprocal of a mean square value of an amplitude of the first reference signal in a predetermined period, the first reference signal being a reference signal before being inputted to the first compressor.

9. The active noise reduction device according to claim 1 ,

wherein while the first compressor outputs the compressed first reference signal, the filter coefficient updater stops updating the coefficient of the adaptive filter.

10. A vehicle comprising:

the active noise reduction device according to claim 1 ; and

the first reference signal source.

11. An active noise reduction method of reducing noise in a space in a vehicle, the active noise reduction method comprising:

compressing and outputting a first reference signal outputted by a first reference signal source, as a compressed first reference signal, the compressed first reference signal having a correlation with the noise, and having an amplitude greater than or equal to a first threshold, the first reference signal source being attached to the vehicle;

applying an adaptive filter to the compressed first reference signal to generate a canceling signal to be used to output a canceling sound for reducing the noise;

updating a coefficient of the adaptive filter using a step size parameter;

adjusting the step size parameter using the first reference signal before being compressed;

receiving an error signal corresponding to a residual sound resulting from interference between the canceling sound and the noise;

compressing and outputting the error signal, as a compressed error signal, the compressed error signal having an amplitude greater than or equal to a second threshold; and

generating a filtered reference signal by correcting at least one of the first reference signal and the compressed first reference signal using simulated transfer characteristics that simulate acoustic transfer characteristics from the canceling signal,

wherein, in the updating, the coefficient of the adaptive filter is updated using the step size parameter, the compressed error signal, and the filtered reference signal.

12. The active noise reduction method according to claim 11 , further comprising:

receiving a second reference signal outputted by a second reference signal source and having a correlation with the noise, the second reference signal source being attached to the vehicle; and

compressing and outputting the second reference signal, as a compressed second reference signal, the compressed second reference signal having an amplitude greater than or equal to a third threshold,

wherein the first reference signal and the second reference signal are compressed at a same compression ratio.

13. The active noise reduction method according to claim 11 , further comprising:

receiving a second reference signal outputted by a second reference signal source and having a correlation with the noise, the second reference signal source being attached to the vehicle; and

compressing and outputting the second reference signal, as a compressed second reference signal, the compressed second reference signal having an amplitude greater than or equal to a third threshold,

wherein when the first reference signal is to be compressed at a first compression ratio and the second reference signal is to be compressed at a second compression ratio, compression ratios of the first reference signal and the second reference signal are each same as a higher one of the first compression ratio and the second compression ratio.

14. The active noise reduction method according to claim 11 ,

wherein the first reference signal and the error signal are compressed at a same compression ratio.

15. The active noise reduction method according to claim 11 ,

wherein when the first reference signal is to be compressed at a first compression ratio and the error signal is to be compressed at a second compression ratio, compression ratios of the first reference signal and the error signal are each same as a higher one of the first compression ratio and the second compression ratio.

16. The active noise reduction method according to claim 11 ,

wherein the filtered reference signal is generated by correcting the first reference signal, outputted by the first reference signal source and before being compressed in the compressing, using the simulated transfer characteristics.

17. The active noise reduction method according to claim 11 ,

wherein the step size parameter is adjusted to a value proportional to a reciprocal of a mean square value of an amplitude of the first reference signal in a predetermined period.

18. The active noise reduction method according to claim 11 ,

wherein, while the compressed first reference signal is being outputted, the updating of the coefficient of the adaptive filter is stopped.