Method and apparatus for extending band of audio signal using higher harmonic wave generator

1. A method for extending a band of an audio signal inputted into a band extending apparatus, said method including the steps of:

responsive to the inputted audio signal having a predetermined band, generating, with a higher harmonic wave generating device, a higher harmonic wave of the inputted audio signal;

generating a first modulated signal by modulating, with a modulator, an amplitude of a generated higher harmonic wave of the audio signal according to a band signal having a predetermined bandwidth;

bandpass-filtering, with a band pass filter, a generated first modulated signal using a predetermined bandpass characteristic and outputting a resultant first modulated signal; and

adding, with an adding device, a bandpass-filtered first modulated signal to the inputted audio signal, and outputting an audio signal having an addition result.

2. The method as claimed in claim 1 , further including a step of changing, with a first level changing device, a level of the band signal, prior to said amplitude modulating step.

3. The method as claimed in claim 1 , further including a step of changing, with a second level changing device, a level of the bandpass-filtered first modulated signal, prior to said adding step.

4. The method as claimed in claim 1 , further including a step of changing, with a level changing device, a level of the inputted audio signal, adding the audio signal having a changed level to the first modulated signal, and outputting a resultant first modulated signal to said bandpass-filtering step, said level changing step executed after said amplitude modulating step and prior to said bandpass-filtering step.

5. The method as claimed in claim 1 , further including a step of generating, with a band generating device, the band signal.

6. The method as claimed in claim 5 ,

wherein said band signal generating step includes a step of generating, with the band generating device, a noise signal having no correlation with the inputted audio signal.

7. The method as claimed in claim 5 ,

wherein said band signal generating step includes a step of generating, with the band generating device, the band signal based on the inputted audio signal.

8. The method as claimed in claim 6 ,

wherein said band signal generating step includes the steps of:

generating, with a random noise generator, a predetermined random noise signal;

calculating, with an absolute value generator, an absolute value of a generated random noise signal, and generating a random noise signal having the absolute value; and

low-pass filtering, with a low pass filter, the random noise signal having the absolute value using a predetermined low-pass characteristic, and outputting a resultant random noise signal as the band signal.

9. The method as claimed in claim 7 ,

wherein said band signal generating step includes the steps of:

generating a second modulated signal by quantizing the inputted audio signal using either one of a delta-sigma modulation type quantizer and a sigma-delta modulation type quantizer, and generating a quantization noise signal during said quantization;

calculating, with an absolute value generator, an absolute value of a generated quantization noise signal, and generating a random noise signal having the absolute value; and

low-pass filtering, with a low pass filter, the random noise signal having the absolute value using a predetermined low-pass characteristic, and outputting a resultant random noise signal as the band signal.

10. The method as claimed in claim 9 ,

wherein said adding step includes a step of adding, with the adding device, an audio signal generated by quantizing the inputted audio signal, instead of the inputted audio signal, to the bandpass-filtered first modulated signal, and outputting an audio signal having an addition result.

11. The method as claimed in claim 1 , further including a step of changing, with a cutoff characteristic changing device, a cutoff characteristic on a lower frequency side of the bandpass characteristic.

12. An apparatus for extending a band of an audio signal, said apparatus comprising:

a higher harmonic wave generating device for generating a higher harmonic wave of an inputted audio signal having a predetermined band based on the inputted audio signal;

an amplitude modulating device for generating a first modulated signal by modulating an amplitude of a generated higher harmonic wave of the audio signal according to a band signal having a predetermined bandwidth;

a bandpass filtering device for bandpass-filtering a generated first modulated signal using a predetermined bandpass characteristic, and for outputting a resultant first modulated signal; and

an adding device for adding a bandpass-filtered first modulated signal to the inputted audio signal, and for outputting an audio signal having an addition result.

13. The apparatus as claimed in claim 12 , further comprising a first level changing device provided at the previous stage of said amplitude modulating device, said first level changing device changing a level of the band signal.

14. The apparatus as claimed in claim 12 , further comprising a second level changing device provided at the previous stage of said adding device, said second level changing device changing a level of the bandpass-filtered first modulated signal.

15. The apparatus as claimed in claim 12 , further comprising a level changing device provided at the subsequent stage of said amplitude modulating device and at the previous stage of said bandpass-filtering device, said level changing device changing a level of the inputted audio signal, adding the audio signal having a changed level to the first modulated signal, and bandpass-filtering a resultant first modulated signal.

16. The apparatus as claimed in claim 12 , further comprising a band signal generating device for generating the band signal.

17. The apparatus as claimed in claim 16 ,

wherein said band signal generating device generates a noise signal having no correlation to the inputted audio signal.

18. The apparatus as claimed in claim 16 ,

wherein said band signal generating device generates the band signal based on the inputted audio signal.

19. The apparatus as claimed in claim 17 ,

wherein said band signal generating device includes:

a device for generating a predetermined random noise signal;

a device for calculating an absolute value of a generated random noise signal, and generating a random noise signal having the absolute value; and

a device for low-pass filtering the random noise signal having the absolute value using a predetermined low-pass characteristic, and outputting a resultant random noise signal as the band signal.

20. The apparatus as claimed in claim 18 ,

wherein said band signal generating device includes:

a device for quantizing the inputted audio signal using either one of a delta-sigma modulation type quantizer and a sigma-delta modulation type quantizer to generate a second modulated signal, and for generating a quantization noise signal during said quantization;

a device for calculating an absolute value of a generated quantization noise signal, and generating a random noise signal having the absolute value; and

a device for low-pass filtering the random noise signal having the absolute value using a predetermined low-pass characteristic, and outputting a resultant random noise signal as the band signal.

21. The apparatus as claimed in claim 20 ,

wherein said adding device adds an audio signal generated by quantizing the inputted audio signal, instead of the inputted audio signal, to the bandpass-filtered first modulated signal, and outputs an audio signal having an addition result.

22. The apparatus as claimed in claim 12 , further comprising a device for changing a cutoff characteristic on a lower frequency side of the bandpass characteristic of said bandpass-filtering device.

23. A computer readable recording medium having a computer program stored thereon for causing a computer to perform a method comprising:

responsive to an inputted audio signal having a predetermined band, generating a higher harmonic wave of the inputted audio signal;

generating a first modulated signal by modulating an amplitude of a generated higher harmonic wave of the audio signal according to a band signal having a predetermined bandwidth;

bandpass-filtering a generated first modulated signal using a predetermined bandpass characteristic and outputting a resultant first modulated signal; and

adding a bandpass-filtered first modulated signal to the inputted audio signal, and outputting an audio signal having an addition result.