Pitch period equalizing apparatus and pitch period equalizing method, and speech coding apparatus, speech decoding apparatus, and speech coding method

• US 7,957,958 B2
• Filed: 03/24/2006
• Issued: 06/07/2011
• Est. Priority Date: 04/22/2005
• Status: Active Grant

• Current Assignee: Kyushu Institute of Technology
• Original Assignee: Kyushu Institute of Technology
• Inventors: Sato, Yasushi
• Primary Examiner(s): Opsasnick; Michael N
• Application Number:
  US11/918,958
• Publication Number:
  US 20090299736A1
• Time in Patent Office: 1,901 Days
• Field of Search: 704/207
• US Class Current: 704/207
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor
• CPC Class Codes: G10L 21/013 Adapting to target pitch

Abstract

To provide a speech coding technology that realizes a low bit rate and can suppress distortion of reproduction speech as compared with a conventional technology.

There are provided pitch detecting means 5 that detects a pitch frequency of an input speech signal, residual calculating means 6 that calculates the difference (residual frequency) between the pitch frequency and a reference frequency, a frequency shifter 4 that shifts a frequency of the input speech signal in proportional to the residual frequency in a direction for being close to the reference frequency and equalizes a pitch period, and orthogonal transforming means that orthogonally transforms the speech signal (pitch-equalizing speech signal) output by the frequency shifter 4 by a constant number of the pitch intervals and generates transforming coefficient data, and waveform coding means that encodes the transforming coefficient data.

Claims

1. A pitch period equalizing apparatus that equalizes a pitch period of voiced sound of an input speech signal, comprising:

pitch detecting means that detects a pitch frequency of the speech signal;

residual calculating means that calculates a residual frequency, as the difference obtained by subtracting a predetermined reference frequency from the pitch frequency; and

a frequency shifter that equalizes the pitch period of the speech signal by shifting the pitch frequency of the speech signal in a direction for being close to the reference frequency on the basis of the residual frequency,

wherein the frequency shifter comprises;

modulating means that modulates an amplitude of the input signal by a predetermined modulating wave and generates the modulated wave;

a band-pass filter that allows only a signal having a single side band component of the modulated wave to selectively pass through;

demodulating means that demodulates the modulated wave subjected to the filtering of the band-pass filter by a predetermined demodulating wave and outputs the demodulated wave as an output speech signal; and

frequency adjusting means that sets, as a predetermined basic carrier frequency, one of a frequency of the modulating wave used for modulation of the modulating means and a frequency of the demodulating wave used for demodulation of the demodulating means, and sets the other frequency to a frequency obtained by subtracting the residual frequency from the basic carrier frequency.

2. The pitch period equalizing apparatus according to claim 1, wherein the pitch detecting means comprises:

input pitch detecting means that detects an input pitch frequency of the input speech signal input to the frequency shifter; and

output pitch detecting means that detects an output pitch frequency of the output speech signal output from the frequency shifter, and

the pitch period equalizing apparatus further comprises;

pitch averaging means that calculates an average pitch frequency as the time-based average of the input pitch frequencies, and

the residual calculating means sets the average pitch frequency as a reference frequency, and calculates a residual frequency as the difference between the output pitch frequency and the reference frequency.

3. The pitch period equalizing apparatus according to claim 1, wherein the pitch detecting means is an input pitch detecting means that detects an input pitch frequency of the input speech signal input to the frequency shifter, and comprises:

pitch averaging means that calculates an average pitch frequency as the time-based average of the input pitch frequencies, and

the residual calculating means sets the average pitch frequency as a reference frequency and calculates a residual frequency as the difference between the input pitch frequency and the reference frequency.

4. The pitch period equalizing apparatus according to claim 1, wherein the pitch detecting means is output pitch detecting means that detects an output pitch frequency of the output speech signal output from the frequency shifter, and comprises:

pitch averaging means that calculates an average pitch frequency as the time-based average of the output pitch frequencies, and

the residual calculating means sets the average pitch frequency as a reference frequency, and calculates a residual frequency between the output pitch frequency and the reference frequency.

5. The pitch period equalizing apparatus according to claim 1, wherein the pitch detecting means is input pitch detecting means that detects an input pitch frequency of the input speech signal input to the frequency shifter, and comprises reference frequency generating means that outputs the reference frequency, and

the residual calculating means calculates a residual frequency as the difference between the input pitch frequency and the reference frequency.

6. The pitch period equalizing apparatus according to claim 1, wherein the pitch detecting means is output pitch detecting means that detects an output pitch frequency of the output speech signal output from the frequency shifter, and comprises:

reference frequency generating means that outputs the reference frequency, and

the residual calculating means calculates a residual frequency as the difference between the output pitch frequency and the reference frequency.

7. A speech coding apparatus that encodes an input speech signal, comprising:

the pitch period equalizing apparatus according to claim 1 that equalizes a pitch period of voiced sound of the speech signal; and

orthogonal transforming means that orthogonally transforms a pitch-equalizing speech signal output by the pitch period equalizing apparatus at an interval of a constant number of pitches, and generates transforming coefficient data of a subband.

8. The speech coding apparatus according to claim 7, further comprising:

resampling means that performs resampling of the pitch-equalizing speech signal output by the pitch period equalizing apparatus so that the number of samples at one pitch interval is constant.

17. A program that is executed by a computer to enable the computer to function as the pitch period equalizing apparatus according to claim 1.

18. A program that is executed by a computer to enable the computer to function as the speech coding apparatus according to claim 7.

9. A speech decoding apparatus that decodes an original speech signal on the basis of a pitch-equalizing speech signal obtained by equalizing a pitch frequency of the original speech signal to a predetermined reference frequency and by resolving the equalized pitch frequency to a subband component with orthogonal transformation and a residual frequency signal as the difference obtained by subtracting the reference frequency from the pitch frequency of the original speech signal, the speech decoding apparatus comprising:

inverse-orthogonal transforming means that restores a pitch-equalizing speech signal by orthogonally inverse-transforming the pitch-equalizing speech signal orthogonally-transformed at a constant number of pitches; and

a frequency shifter that generates the restoring speech signal by shifting the pitch frequency of the pitch-equalizing speech signal to be close to a frequency obtained by adding the residual frequency to the reference frequency, and

wherein the frequency shifter comprises;

modulating means that modulates an amplitude of the pitch-equalizing speech signal by a predetermined modulating wave and generates the modulated wave;

a band-pass filter that allows only a signal of a single side band component of the modulated signal to selectively pass through;

demodulating means that demodulates the modulated wave subjected to the filtering by the band-pass filter by a predetermined demodulating wave and outputs the demodulated wave as a restoring speech signal; and

frequency adjusting means that sets, as a predetermined basic carrier frequency, one of a frequency of the modulating wave used for modulation by the modulating means and a frequency of the demodulating wave used for demodulation by the demodulating means, and sets the other frequency to a value obtained by adding the residual frequency to the basic carrier frequency.

19. A program that is executed by a computer to enable the computer to function as the speech decoding apparatus according to claim 9.

10. A pitch period equalizing method that equalizes a pitch period of voiced sound of an input speech signal using a pitch period equalizing apparatus, the pitch period equalizing method comprising:

a frequency shifting step of inputting the input speech signal to a frequency shifter and obtaining an output speech signal from the frequency shifter;

an output pitch detecting step using an output pitch detecting means for detecting an output pitch frequency of the output speech signal; and

a residual frequency calculating step using a residual calculating means for calculating a residual frequency as the difference between the output pitch frequency and a predetermined reference frequency,

wherein the frequency shifting step comprises;

a frequency setting step of setting one of a frequency of a modulating wave used for modulation and a frequency of a demodulating wave used for demodulation to a predetermined basic carrier frequency, and setting the other frequency to a frequency obtained by subtracting the residual frequency calculated by the residual frequency calculating step from the basic carrier frequency;

a modulating step of modulating an amplitude of the input speech signal by the modulating wave and generating the modulated wave;

a band reducing step of performing filtering of the modulated wave by a band-pass filter that allows only a single side band component of the modulated wave to pass through; and

a demodulating step of demodulating the modulated wave subjected to the filtering of the band-pass filter by the demodulating wave and outputting the demodulated wave as an output speech signal.

11. The pitch period equalizing method according to claim 10, further comprising:

a pitch averaging step of calculating an average pitch frequency as the time-based average of the output pitch frequencies,

wherein the residual frequency calculating step uses the residual calculating means to calculate the difference between the output pitch frequency and the average pitch frequency, and sets the calculated difference as the residual frequency.

12. The pitch period equalizing method according to claim 10, further comprising:

an input pitch detecting step using an input pitch detecting means for detecting an input pitch frequency of the input speech signal; and

a pitch averaging step of calculating an average pitch frequency as the time-based average of the input pitch frequencies,

wherein the residual frequency calculating step using the residual calculating means to calculate the difference between the output pitch frequency and the average pitch frequency, and sets the calculated difference as the residual frequency.

15. A speech coding method that encodes an input speech signal, comprising:

a pitch period equalizing step of equalizing a pitch period of voiced sound of the speech signal with the pitch period equalizing method according to claim 10;

an orthogonal transforming step of orthogonally transforming a pitch-equalizing speech signal equalized by the pitch period equalizing step at a constant number of pitches, and generating transforming coefficient data of a subband; and

a waveform coding step of encoding the transforming coefficient data.

13. A pitch period equalizing method that equalizes a pitch period of voiced sound of an input speech signal using a pitch period equalizing apparatus, the pitch period equalizing method comprising:

an input pitch detecting step using an input pitch detecting means for detecting an input pitch frequency of the input speech signal;

a frequency shifting step of inputting the input speech signal to a frequency shifter and obtaining an output speech signal from the frequency shifter; and

a residual frequency calculating step of calculating a residual frequency as the difference obtained by subtracting a predetermined reference frequency from the input pitch frequency,

wherein the frequency shifting step comprises;

a frequency setting step of setting one of a frequency of a modulating wave used for modulation and a frequency of a demodulating wave used for demodulation to a predetermined basic carrier frequency, and setting the other frequency to a frequency obtained by subtracting the residual frequency calculated by the residual frequency calculating step from the basic carrier frequency;

a modulating step of modulating an amplitude of the input speech signal by the modulating wave and generating a modulated wave;

a band reducing step of performing filtering of the modulated wave by a band-pass filter that allows only a single side band component of the modulated wave; and

a demodulating step of demodulating the modulated wave subjected to the filtering with the band-pass filter by the demodulating wave and outputting the demodulated wave as an output speech signal.

14. The pitch period equalizing method according to claim 13, further comprising:

a pitch averaging step of calculating an average pitch frequency as the time-based average of the input pitch frequencies,

wherein the residual frequency calculating step calculates the difference between the input pitch frequency and the average pitch frequency, and sets the calculated difference as the residual frequency.

16. The speech coding method according to claim 14, further comprising:

a resampling step of performing resampling of the pitch-equalizing speech signal equalized by the pitch period equalizing step so that the number of samples at one pitch interval is constant.

20. A speech coding method that encodes an input speech signal, comprising:

a pitch period equalizing step of equalizing a pitch period of voiced sound of the speech signal with the pitch period equalizing method according to claim 13;

an orthogonal transforming step of orthogonally transforming a pitch-equalizing speech signal equalized by the pitch period equalizing step at a constant number of pitches, and generating transforming coefficient data of a subband; and

a waveform coding step of encoding the transforming coefficient data.