Band extending apparatus and method

• US 7,684,979 B2
• Filed: 05/02/2005
• Issued: 03/23/2010
• Est. Priority Date: 10/31/2002
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Ozawa, Kazunori
• Primary Examiner(s): Han; Qi
• Application Number:
  US11/118,337
• Publication Number:
  US 20050256709A1
• Time in Patent Office: 1,786 Days
• Field of Search: 704/226, 704/205, 704/220
• US Class Current: 704/226
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

A band extending apparatus includes a spectral parameter calculating circuit for calculating spectral parameters of a narrow-band input signal, a coefficient calculating circuit supplied with the spectral parameters to convert the spectral parameters into coefficients of a band extended signal, and a gain circuit supplied with a gain from a gain adjustment circuit and multiplying an output signal of a noise generating circuit with the gain to output the resulting signal to a synthesis filter circuit. The synthesis filter circuit forms a filter by receiving coefficients from the coefficient calculating circuit. The signal from the gain circuit is passed through the filter. The synthesis filter circuit outputs a high band signal for band extension. The band extending apparatus also includes a sampling frequency converting circuit, supplied with the narrow-band input signal to output a signal up-sampled to a preset sampling frequency, and an adder for summing the high band signal to the up sampled signal to output a band extended signal.

Claims

1. A band extending apparatus comprising:

a spectral parameter calculating unit, receiving at least an input signal of a preset frequency band to calculate spectral parameters representing spectral characteristics;

a noise generating unit for generating a noise signal;

a coefficient calculating unit for shifting the frequency of said spectral parameters to then find filter coefficients;

a gain unit for supplying a gain to an output of said noise generating unit;

a synthesis filter unit for passing an output signal of said gain unit through a synthesis filter, formed using said filter coefficients, to reproduce a signal for band extension;

means for adding a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to generate a band extended signal; and

a voiced/unvoiced discriminating circuit, receiving said input signal of the preset frequency band, to verify whether the input signal in terms of a frame as a unit is voiced or unvoiced;

wherein said gain unit includes;

a gain adjustment unit, receiving voiced/unvoiced discrimination information output from said voiced/unvoiced discriminating circuit, to adjust the gain to be imparted to the output signal of said noise generating circuit, depending on whether said voiced/unvoiced discrimination information indicates voiced or unvoiced; and

a gain circuit, receiving said gain adjusted by said gain adjustment unit to multiply the output signal of said noise generating unit with said gain to output the resulting signal.

2. The band extending apparatus as defined in claim 1, wherein said voiced/unvoiced discriminating circuit derives a normalized autocorrelation function up to a preset delay time, for said input signal of the preset band, and verifies whether the input signal is voiced or unvoiced, based on the relative magnitude of the maximum value of said normalized autocorrelation function and a preset threshold value, to output said voiced/unvoiced discrimination information.

3. The band extending apparatus as defined in claim 1, wherein

a post-filter is formed using weighting coefficients as weighted version of filter coefficients output from said coefficient calculating unit, and wherein an output signal of said synthesis filter unit is passed through said post-filter to reproduce the signal for band extension.

4. The band extending apparatus as defined in claim 3, wherein said means for summing the signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to generate a band extended signal includes

a sampling frequency converting circuit for up-sampling said input signal with a pre-set sampling frequency to output the resulting up-sampled signal;

and

an adder, receiving and summing an output signal of said sampling frequency converting circuit and an output signal of said post-filter to output the resulting sum signal as said band extended signal.

5. The band extending apparatus as defined in claim 1, wherein

said means for summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to generate a band extended signal includes:

a sampling frequency converting circuit for up-sampling said input signal with a pre-set sampling frequency to output the resulting up-sampled signal; and

an adder, receiving and summing an output signal of said sampling frequency converting circuit and an output signal of said synthesis filter to output the resulting sum signal as said band extended signal.

6. A band extending apparatus comprising:

a spectral parameter calculating unit, receiving at least an input signal of a preset frequency band to calculate spectral parameters representing spectral characteristics;

an adaptive codebook unit, calculating a pitch period at least from said input signal to generate an adaptive codebook component based on said pitch period and a past sound source signal;

a noise generating unit for generating a noise signal;

a coefficient calculating unit for shifting the frequency of said spectral parameters to find filter coefficients;

a gain unit for supplying a gain to at least one of an output signal of said noise generating unit and an output signal of said adaptive codebook unit and outputting a sound source signal;

a synthesis filter unit, receiving said sound source signal from said gain unit to a synthesis filter formed using said filter coefficients to reproduce a signal for band extension;

means for summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to produce a band extended signal; and

a voiced/unvoiced discriminating circuit, receiving said input signal of the preset frequency band, to verify whether the input signal in terms of a frame as a unit is voiced or unvoiced, and for supplying, for a voiced frame, a preset delay derived from said voiced/unvoiced decision, as a pitch period to an adaptive codebook circuit forming said adaptive codebook unit;

said adaptive codebook circuit, receiving the delay from said voiced/unvoiced discriminating circuit, as a delay of said adaptive codebook, generating an adaptive codebook signal based on the past sound source signal, and outputting the adaptive codebook signal generated;

said gain unit including;

a gain adjustment unit, receiving voiced/unvoiced discrimination information from said voiced/unvoiced discriminating circuit, to adjust the gain of the output signal of said adaptive codebook circuit and the gain of the output signal of said noise generating unit, to output the resulting signals, depending on whether said voiced/unvoiced discrimination information indicates voiced or unvoiced;

a gain circuit, receiving said gain from said gain adjustment circuit to multiply at least one of the output signal of said adaptive codebook circuit and the output signal of said noise generating circuit with said gain to output the sound source signal; and

an adder for summing two output signals from said gain circuit to output the results of addition to said synthesis filter and to said adaptive codebook circuit.

7. The band extending apparatus as defined in claim 6, wherein said voiced/unvoiced discriminating circuit derives a normalized autocorrelation function up to a preset delay time, for said input signal of the preset band, and verifies whether the input signal is voiced or unvoiced, based on the relative magnitude of the maximum value of said normalized autocorrelation function and a preset threshold value, to output said voiced/unvoiced discrimination information, and wherein said voiced/unvoiced discriminating circuit outputs, for a voiced frame, the delay maximizing said normalized autocorrelation function as a pitch period.

8. The band extending apparatus as defined in claim 6, further comprising:

a low-pass filter, receiving an output signal of said adaptive codebook unit as an input.

9. A band extending apparatus comprising:

a spectral parameter calculating unit, receiving at least with an input signal of a preset frequency band to calculate spectral parameters representing spectral characteristics;

an adaptive codebook unit for calculating a pitch period at least from said input signal to generate an adaptive codebook component based on said pitch period and past sound source signal;

a noise generating unit for generating a noise signal;

a coefficient calculating unit for shifting the frequency of said spectral parameters to then find filter coefficients;

a gain unit for supplying a gain to at least one of an output of said noise generating unit and an output signal of said adaptive codebook unit and outputting a sound source signal;

a pitch pre-filter for filtering said sound source signal from said gain unit, using said pitch period;

a synthesis filter unit for supplying an output signal of said pitch pre-filter to a synthesis filter formed using said filter coefficients to generate band-expanding signal;

means for summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to generate a band extended signal; and

a voiced/unvoiced discriminating circuit, receiving said input signal of the preset frequency band, to verify whether the input signal in terms of a frame as a unit is voiced or unvoiced, and for supplying, for a voiced frame, a preset delay derived from said voiced/unvoiced decision, as a pitch period, to an adaptive codebook circuit forming said adaptive codebook unit and to said pitch pre-filter;

said adaptive codebook circuit, receiving a delay from said voiced/unvoiced discriminating circuit as a delay of the adaptive codebook to generate and output an adaptive codebook signal based on a past sound source signal;

said gain unit including;

a gain adjustment circuit, receiving voiced/unvoiced discrimination information from said voiced/unvoiced discriminating circuit, to adjust the gain of the output signal of said adaptive codebook circuit and the gain of the output signal of said noise generating unit, to output the resulting signals, depending on whether said voiced/unvoiced discrimination information indicates voiced or unvoiced; and

a gain circuit receiving said gain from said gain adjustment circuit to multiply at least one of the output signal of said adaptive codebook circuit and the output signal of said noise generating unit with said gain, to sum two resulting output signals, at least one of which has been multiplied with said gain, to output the result of addition to said pitch pre-filter;

an output signal of said pitch pre-filter being supplied to said synthesis filter and to said adaptive codebook circuit.

10. A band extending apparatus comprising:

a spectral parameter calculating unit, receiving at least with an input signal of a preset frequency band to calculate spectral parameters representing spectral characteristics;

a pitch generating unit, calculating a pitch period at least from said input signal to generate a period signal using said pitch period;

a noise generating unit for generating a noise signal;

a coefficient calculating unit for shifting the frequency of said spectral parameters to find filter coefficients;

a gain unit for supplying a proper gain to at least one of an output signal of said noise generating unit and an output signal of said pitch generating unit and outputting a sound source signal;

a synthesis filter unit, receiving said sound source signal from said gain unit to a synthesis filter, formed using said filter coefficients, to reproduce a signal for band extension;

means for summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit, to produce a band extended signal; and

a voiced/unvoiced discriminating circuit, receiving said input signal of the preset frequency band, to verify whether the input signal in terms of a frame as a unit is voiced or unvoiced, and for supplying, for a voiced frame, a preset delay derived from said voiced/unvoiced decision, as a pitch period, to said pitch generating unit;

said gain unit including;

a gain adjustment circuit, receiving voiced/unvoiced discrimination information output from said voiced/unvoiced discriminating circuit, to adjust the gain of the output signal of said pitch generating unit and the gain of said noise generating circuit, depending on whether said voiced/unvoiced discrimination information indicates voiced or unvoiced to output the resulting signals;

a gain circuit, receiving said gain from said gain adjustment circuit to multiply at least one of the output signal of said pitch generating unit and the output signal of said noise generating circuit with said gain to output the sound source signal; and

an adder for summing the two output signals from said gain circuit to output the results of addition to said synthesis filter.

11. A band extending apparatus comprising:

a spectral parameter calculating unit, receiving at least an input signal of a preset frequency band to calculate spectral parameters representing spectral characteristics;

a pitch generating unit for calculating a pitch period at least from said input signal to generate a period signal using said pitch signal;

a noise generating unit for generating a noise signal;

a coefficient calculating unit for shifting the frequency of said spectral parameters to then find filter coefficients;

a gain unit for supplying a gain to at least one of an output signal of said noise generating unit and an output signal of said pitch generating unit and for outputting a sound source signal;

a pitch pre-filter for filtering said sound source signal from said gain unit, using said pitch period;

a synthesis filter unit, receiving an output signal of said pitch pre-filter to reproduce a signal for band extension;

means for summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to obtain a band extended signal; and

a voiced/unvoiced discriminating circuit, receiving said input signal of the preset frequency band, to verify whether the input signal in terms of a frame as a unit is voiced or unvoiced, and for supplying, for a voiced frame, a preset delay derived from said voiced/unvoiced decision, as a pitch period to said pitch generating unit and to said pitch pre-filter;

said gain unit including;

a gain adjustment circuit, receiving voiced/unvoiced discrimination information, output from said voiced/unvoiced discriminating circuit, to adjust the gain of the output signal of said pitch generating unit and the gain of said noise generating circuit, depending on whether said voiced/unvoiced discrimination information indicates voiced or unvoiced, to output the resulting signals; and

a gain circuit, receiving said gain from said gain adjustment unit to multiply at least one of the output signal of said pitch generating unit and the output signal of said noise generating circuit with said gain to output the results of addition of two resulting signals to said synthesis filter.

12. A band extending method comprising:

receiving at least an input signal of a preset frequency band to calculate spectral parameters representing spectral characteristics;

shifting the frequency of said spectral parameters to then find filter coefficients;

supplying a gain to a noise signal generated by a noise generating unit;

passing a signal, added by said gain, through a synthesis filter, formed using said filter coefficients, to reproduce a signal for band extension;

summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to generate a band extended signal;

verifying, by a voiced/unvoiced discriminating circuit, supplied with aid input signal of the preset frequency band, whether a signal in terms of a frame as a unit is voiced or unvoiced;

adjusting the gain of the output signal of said noise generating unit, depending on the results of voiced/unvoiced discrimination; and

outputting a signal corresponding to the output signal of said noise generating unit multiplied by said adjusted gain to said synthesis filter.

13. The band extending method as defined in claim 12, further comprising:

deriving, by said voiced/unvoiced discriminating circuit, a normalized autocorrelation function up to a preset delay time, for said input signal of the preset frequency band, and verifying whether the input signal is voiced or unvoiced, based on the relative magnitude of the maximum value of said normalized autocorrelation function and a preset threshold value, to output said voiced/unvoiced discrimination information.

14. The band extending method as defined in claim 12, comprising:

passing an output signal of said synthesis filter through a post-filter formed using weighting coefficients corresponding to weighted version of said filter coefficients to reproduce the signal for band extension.

15. The band extending method as defined in claim 14, wherein the processing of summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to generate a band extended signal includes:

up-sampling said input signal with a pre-set sampling frequency to output the resulting up-sampled signal; and

receiving and summing said up-sampled signal and an output signal of said post-filter to output the resulting sum signal as said band extended signal.

16. The band extending method as defined in claim 12, wherein the processing of summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to generate a band extended signal, includes:

up-sampling said input signal with a pre-set sampling frequency to output the resulting up-sampled signal; and

receiving and summing said up-sampled signal and an output signal of said synthesis filter to output the resulting sum signal as said band extended signal.

17. A band extending method comprising:

receiving at least an input signal of a preset frequency band to calculate spectral parameters representing spectral characteristics;

calculating a pitch period at least from said input signal to generate an adaptive codebook component based on said pitch period and a past sound source signal;

shifting the frequency of said spectral parameters to find filter coefficients;

supplying a gain to at least one of a noise signal from a noise generating unit and to said adaptive codebook component and outputting a sound source signal;

receiving said sound source signal from said gain unit to a synthesis filter formed using said filter coefficients to reproduce a signal for band extension;

summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to obtain a band extended signal;

discriminating whether a signal in terms of a frame as a unit is voiced or unvoiced, by a voiced/unvoiced discriminating circuit, receiving said input signal of the preset frequency band, and for supplying, for a voiced frame, a preset delay derived from said voiced/unvoiced decision, as a pitch period, to an adaptive codebook circuit;

receiving, by said adaptive codebook circuit, the delay from said voiced/unvoiced discriminating circuit, as a delay of said adaptive codebook, and generating and output an adaptive codebook signal, based on past sound source signal;

receiving voiced/unvoiced discrimination information from said voiced/unvoiced discriminating circuit, and adjusting the gain of the output signal of said adaptive codebook circuit and the gain of the output signal of said noise generating unit, to output the resulting signals, depending on whether said voiced/unvoiced discrimination information indicates voiced or unvoiced;

multiplying at least one of the output signal of said adaptive codebook circuit and the output signal of said noise generating circuit with said adjusted gain to output the sound source signal; and

summing two output signals, at least one of which has been multiplied with said gain, to output the results of addition to said synthesis filter and to said adaptive codebook circuit.

18. The band extending method as defined in claim 17, further comprising:

deriving, by said voiced/unvoiced discriminating circuit, a normalized autocorrelation function up to a preset delay time, for said input signal of the preset frequency band, and verifying whether the input signal is voiced or unvoiced, based on the relative magnitude of the maximum value of said normalized autocorrelation function and a preset threshold value, outputting said voiced/unvoiced discrimination information, and outputting, for a voiced frame, the delay maximizing said normalized autocorrelation function as a pitch period.

19. The band extending method as defined in claim 17, further comprising:

processing said adaptive codebook component with a low-pass filter to allow frequency components not higher than a preset cut-off frequency to pass therethrough.

20. A band extending method comprising:

receiving at least an input signal of a preset frequency band to calculate spectral parameters representing spectral characteristics;

calculating a pitch period at least from said input signal to generate an adaptive codebook component based on said pitch period and the past sound source signal;

shifting the frequency of said spectral parameters to then find filter coefficients;

supplying a gain to at least one of a noise signal from a noise generating unit and said adaptive codebook component and outputting a sound source signal;

pre-filtering said sound source signal, using said pitch period;

supplying the results of processing of said pitch pre-filter to a synthesis filter formed using said filter coefficients to generate a signal for band extension;

summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to generate a band extended signal;

discriminating, by a voiced/unvoiced discriminating circuit, supplied with said input signal of the preset frequency band, whether the input signal in terms of a frame as a unit is voiced or unvoiced, and for supplying, for a voiced frame, a preset delay derived from said voiced/unvoiced decision, as a pitch period, to an adaptive codebook circuit and to said pitch pre-filter;

receiving, by said adaptive codebook circuit, a delay from said voiced/unvoiced discriminating circuit as a delay of the adaptive codebook to generate and output an adaptive codebook signal based on the past sound source signal;

receiving voiced/unvoiced discrimination information from said voiced/unvoiced discriminating circuit, and adjusting the gain of the output signal of said adaptive codebook circuit and the gain of the output signal of said noise generating unit, to output the resulting signals, depending on whether said voiced/unvoiced discrimination information indicates voiced or unvoiced; and

multiplying at least one of the output signal of said adaptive codebook circuit and the output signal of said noise generating unit with said adjusted gain and summing two resulting output signals, at least one of which has been multiplied with said gain, to output the result of addition to said pitch pre-filter; and

supplying an output signal of said pitch pre-filter to said synthesis filter and to said adaptive codebook circuit.

21. A band extending method comprising:

receiving at least an input signal of a preset frequency band to calculate spectral parameters representing spectral characteristics;

calculating a pitch period at least from said input signal to generate a period signal using said pitch period;

shifting the frequency of said spectral parameters to find filter coefficients;

supplying a gain to at least one of a noise signal of said noise generating unit and said period signal and outputting a sound source signal;

receiving said sound source signal to a synthesis filter formed using said filter coefficients to reproduce a signal for band extension;

summing a signal, corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to obtain a band extended signal;

verifying, by a voiced/unvoiced discriminating circuit, supplied with the input signal of the preset frequency band, whether the input signal in terms of a frame as a unit is voiced or unvoiced, and for supplying, for a voiced frame, a preset delay derived from said voiced/unvoiced decision, as a pitch period, to said pitch generating unit;

receiving voiced/unvoiced discrimination information from said voiced/unvoiced discriminating circuit, and adjusting the gain of the output signal of said pitch generating unit and the gain of said noise generating circuit, depending on whether said voiced/unvoiced discrimination information indicates voiced or unvoiced;

multiplying at least one of the output signal of said pitch generating unit and the output signal of said noise generating circuit with said adjusted gain to output the sound source signal; and

summing the two output signals and outputting the results of addition to said synthesis filter.

22. A band extending method comprising:

receiving at least an input signal of a preset frequency band and calculating spectral parameters representing spectral characteristics;

calculating a pitch period at least from said input signal to generate a period signal using said pitch signal;

shifting the frequency of said spectral parameters to then find filter coefficients;

supplying a gain to at least one of an output signal of said noise generating unit and said pitch signal and outputting a sound source signal;

pre-filtering said sound source signal using said pitch period;

receiving a signal representing the result of processing by said pitch pre-filter to a synthesis filter formed using said pitch period to reproduce a signal for band extension;

summing a signal corresponding to said input signal converted in a sampling frequency thereof to an output signal of said synthesis filter unit to produce a band extended signal;

verifying, by a voiced/unvoiced discriminating circuit, supplied with the input signal of said preset frequency band, whether the input signal in terms of a frame as a unit is voiced or unvoiced, and supplying, for a voiced frame, a preset delay derived from said voiced/unvoiced decision, as a pitch period, to said pitch generating unit;

adjusting the gain of the output signal of said pitch generating unit and the gain of said noise generating circuit, depending on whether said voiced/unvoiced discrimination information from said voiced/unvoiced discriminating circuit indicates voiced or unvoiced; and

multiplying at least one of the output signal of said pitch generating unit and the output signal of said noise generating circuit with said adjusted gain to output the results of addition of two output signals, at least one of which has been multiplied with said gain, to said synthesis filter.