Speech coding system and method using time-separated coding algorithm

• US 6,662,153 B2
• Filed: 01/24/2001
• Issued: 12/09/2003
• Est. Priority Date: 09/19/2000
• Status: Active Grant

• Current Assignee: Pantech Corporation (Ideahub, Inc.)
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Lee, In Sung, Kim, Jong Hark, Park, Man Ho, Yoon, Byung Sik, Choi, Song In, Kim, Dae Sik, Kim, Hyoung Jung
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): NOLAN, DANIEL A
• Application Number:
  US09/769,068
• Publication Number:
  US 20020052737A1
• Time in Patent Office: 1,049 Days
• Field of Search: 704/214, 704/200, 704/230, 704/267, 704/268, 704/208, 704/203, 704/205, 704/216, 704/219
• US Class Current: 704/214
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders

Abstract

A time-separated speech coder that codes a transitional signal of voiced/unvoiced sound through harmonic speech coding, the coder including a transitional excitation signal analyzer/synthesizer for coding the transitional signal by extracting the harmonic model parameters of both transitional analyzers after detecting a transitional point and generating sinusoidal waveforms according to a variable transitional point separating both transitional analyzers. By the transitional point at which energy varies abruptly and the time-separated coding based on the transitional point, more improved speech quality than in the general harmonic speech coder can be obtained using the time-separated speech coder by increasing the representation capability of the transitional signal with large energy variation, after adapting it to the variable transitional point.

Claims

1. A time-separated speech coder for coding the transitional signal of voiced/unvoiced sound through harmonic speech coding, the time-separated speech coder comprises:

an excitation signal transitional analyzer analyzing means which comprises;

a transitional point detecting means for detecting a transitional point to notify the transitional analyzer of said transitional signal;

a harmonic excitation signal analyzing means including window means for extracting harmonic model parameter of each block by applying a Time Warp Hamming (TWH) window to a central point of each left/right block after dividing a Linear Prediction Coefficient (LPC) residual signal which is one of the inputted signals within the transitional analyzer centering said detected transitional point; and

a harmonic excitation signal synthesizing means for adding said harmonic model parameter.

2. The time-separated speech coder according to claim 1, wherein said transitional point detecting means detects said transitional point by measuring abruptly varying degree of the energy ratio of left/right block after computing the left/right energy ratio value E_rate(n) for certain time n.

3. The time-separated speech coder according to claim 2, wherein the computation of left/fight energy ratio value E_rate(n) for said time n is comprised by using the following equation:

$\begin{array}{c}{E}_{\min }<br><br>\left(n\right)=\min <br><br>\left[\underset{i=0}{\overset{P}{\sum <br><br>}}<br><br>s^2<br><br>\left(n+i\right),\underset{i=0}{\overset{P}{\sum <br><br>}}<br><br>s^2<br><br>\left(n-i\right)\right]\\ E_{\max }<br><br>\left(n\right)=\max <br><br>\left[\underset{i=0}{\overset{P}{\sum <br><br>}}<br><br>s^2<br><br>\left(n+i\right),\underset{i=0}{\overset{P}{\sum <br><br>}}<br><br>s^2<br><br>\left(n-i\right)\right]\\ E_{\mathrm{rate}}<br><br>\left(n\right)={\left[\frac{E_{\max }-E_{\min }}{E_{\max }}\right]}^2\end{array}$

where, P is the pitch period, s(n) represents the speech signal after passing a Direct Current removal filter, min(x,y) is the function selecting the smaller number out of x and y, and max(x,y) is the function selecting the larger number out of x and y.

4. The time-separated speech coder according to claim 1, wherein said TWH window ω

is represented in the following equation;

$\begin{array}{c}\mathrm{\omega <br><br>}<br><br>\left(c,n\right)=\text{\hspace{1em}<br><br>}<br><br>\{\begin{array}{cc}{\mathrm{\omega <br><br>}}_h<br><br>\left(c,n\right);<br><br>& 0\le <br><br>c\le <br><br>\frac{\left(N-1\right)}{2}\\ {\mathrm{\omega <br><br>}}_h<br><br>\left(128-c,128-n\right);<br><br>& \frac{\left(N-1\right)}{2}\le <br><br>c\le <br><br>\left(N-1\right)\\ 0;<br><br>& \mathrm{otherwise}\end{array}\\ {\mathrm{\omega <br><br>}}_h<br><br>\left(c,n\right)=\text{\hspace{1em}<br><br>}<br><br>0.54-0.46<br><br>\cos <br><br>\left(2<br><br>\mathrm{\pi <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{f_{\mathrm{\omega <br><br>}}<br><br>\left(c,n\right)}{N-1}\right)\\ f_{\mathrm{\omega <br><br>}}<br><br>\left(c,n\right)=\text{\hspace{1em}<br><br>}<br><br>\frac{N-1}{2<br><br>\log <br><br>\left(\frac{N-1-c}{c}\right)}<br><br>\log <br><br>\left(1+\frac{N-1-2<br><br>c}{c}<br><br>n\right);<br><br>c\le <br><br>\frac{\left(N-1\right)}{2}\end{array}$

where, c is the center of the block, and N represents the number of samples of analysis frame.

5. The time-separated speech coder according to claim 1, wherein said window means adjust two blocks'"'"' energies to the original signal through gain control before using as input of harmonic analysis by applying the TWH window to said energies of left/right block.

6. The time-separated speech coder according to claim 5, wherein said gain control is performed through the following equation:

$G=K<br><br>\sqrt{\left(\frac{\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br>{s<br><br>\left(k\right)}^2}{\underset{k=1}{\overset{N}{\sum <br><br>}}<br><br>{s_{\mathrm{\omega <br><br>}}<br><br>\left(k\right)}^2}<br><br>\frac{N}{n}\right)}$

where, s(k) is the input signal prior to window treatment, s_w(k) represents the input signal which is TWH window treated and N, n, and K represent the length of total frame, the length of the transitional analyzer and the mean energy of the window, respectively.

7. The time-separated speech coder according to claim 1, wherein said harmonic excitation signal synthesizing means guarantees the linear phase of each frame by making the synthesis length and synthesis start position in synthesizing the extracted model parameter,

(a) in the case of non-transitional analyzer, makes the synthesis length as “

L−

st<sup>k−

1</sup>”

, the synthesis buffer start position as “

st<sup>k−

1</sup>” and

finally “

st^k”

value as 0;

(b) in the case of transitional analyzer, divides into the first and the second section, and in the first section makes the synthesis length as “

L/80+l−

st<sup>k−

1</sup>” and

synthesis buffer start position as “

st<sup>k−

1</sup>” and

in the second section makes the synthesis length as “

L/2”

, the synthesis buffer start position as “

80+l” and

finally “

st^k”

value as l, wherein the transitional point, the synthesis length of each block and the frame length are defined as 2l, 160 samples and L, respectively.

8. A time-separated speech coding method for coding the transitional signal of voiced/unvoiced sound through harmonic speech coding, comprising the steps of:

a transitional point detecting step for detecting the transitional point of the transitional signal;

a window applying step for extracting harmonic model parameter of each block by applying TWH window to the central point of left/right block after dividing LPC residue signal out of inputted signals centering said transitional point; and

a synthesis step for adding said harmonic model parameter.

9. The time-separated speech coder according to claim 8, wherein said synthesis step guarantees the linear phase of each frame by making the synthesis length and synthesis start position in order to use an Inverse Fast Fourier Transform (IFFT) synthesis algorithm,

(a) in the case of non-transitional analyzer, makes the synthesis length as “ L−

st<sup>k−

1</sup>”

, the synthesis buffer start position as “

st<sup>k−

1</sup>” and

finally “

st^k”

value as 0;

(b) in the case of transitional analyzer, divides into the first and the second section, and in the first section makes the synthesis length as “

L/80+l−

st<sup>k−

1</sup>” and

synthesis buffer start position as “

st<sup>k−

1</sup>” and

in the second section makes the synthesis length as “

L/2”

, the synthesis buffer start position as “

80+l” and

finally “

st^k”

value as l, wherein the transitional point, the synthesis length of each block and the frame length are defined as 2l, 160 samples and L, respectively.

10. A time-separated speech coder for coding a transitional signal of voiced and unvoiced sound through harmonic speech coding, the time-separated speech coder comprising:

an excitation signal transitional analyzer, comprising;

a transitional point detector configured to detect a transitional point of the transitional signal by measuring abruptly varying degrees of the energy ratio of a left and right signal block after computing a left and right energy ratio value E_rate(n) for a time n, a computation using the following equation;

$\begin{array}{c}{E}_{\min }<br><br>\left(n\right)=\min <br><br>\left[\underset{i=0}{\overset{P}{\sum <br><br>}}<br><br>s^2<br><br>\left(n+i\right),\underset{i=0}{\overset{P}{\sum <br><br>}}<br><br>s^2<br><br>\left(n-i\right)\right]\\ E_{\max }<br><br>\left(n\right)=\max <br><br>\left[\underset{i=0}{\overset{P}{\sum <br><br>}}<br><br>s^2<br><br>\left(n+i\right),\underset{i=0}{\overset{P}{\sum <br><br>}}<br><br>s^2<br><br>\left(n-i\right)\right]\\ E_{\mathrm{rate}}<br><br>\left(n\right)={\left[\frac{E_{\max }-E_{\min }}{E_{\max }}\right]}^2\end{array}$

 

where, P is the pitch period, s(n) represents the speech signal after passing a Direct Current removal filter, min(x,y) is the function selecting the smaller number out of x and y, and max(x,y) is the function selecting the larger number out of x and y;

a harmonic excitation signal analyzer for extracting a harmonic model parameter of each left and right block; and

a harmonic excitation signal synthesizer for adding the harmonic model parameter.