Pitch modification method by glottal closure interval extrapolation

• US 6,125,344 A
• Filed: 08/21/1998
• Issued: 09/26/2000
• Est. Priority Date: 11/28/1997
• Status: Expired due to Fees

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Lee, Jung Chul, Kang, Dong Gyu, Park, Jun, Kim, Sang Hun
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Nolan, Daniel A.
• Application Number:
  US09/137,606
• Time in Patent Office: 767 Days
• Field of Search: 704/220, 704/201, 704/205-208, 704/223, 704/264
• US Class Current: 704/207
• CPC Class Codes: G10L 21/003 Changing voice quality, e.g. pitch or formants
• CPC Class Codes: G10L 21/013 Adapting to target pitch
• CPC Class Codes: G10L 21/04 Time compression or expansion

Abstract

The present invention relates to an improved pitch modification method by glottal closure interval extrapolation. It is an object of the present invention to modify pitches of speech signals by the glottal closure interval extrapolation and to maintain quality of the modified speech, when concatenating original speech segments to synthesize speech. An input speech signal is converted into a digital speech signal. A glottal closure interval is detected in the digital speech signal so as to estimate vocal tract parameters by using pitch synchronous analysis. Vocal tract characteristic signals of the glottal closure interval and glottal characteristic signals of a glottal open interval are separated from each other according to the detected glottal closure interval. The separated vocal tract characteristic signals are extrapolated and reduced to a desired pitch length by the estimated vocal tract parameter. The extrapolated and reduced vocal tract characteristic signals are overlapped and added to the separated glottal characteristic signal so as to generate a synthetic speech signal which varies in a desired pitch length.

Claims

1. An improved pitch modification method for producing a pitch modified digital speech signal of an input speech signal by glottal closure interval extrapolation, comprising steps of:

(a) converting said input speech signal into an electric analog speech signal;

(b) converting said electric analog speech signal into a digital speech signal;

(c) detecting a glottal closure interval in said digital speech signal, and estimating vocal tract parameters using pitch synchronous analysis;

(d) separating vocal tract characteristic signals of the glottal closure interval and glottal characteristic signals of a glottal open interval from each other according to the glottal closure interval detected at the step (c);

(e) extrapolating the vocal tract characteristic signals separated at step (d) to a desired pitch length by using the vocal tract parameter estimated at the step (c); and

(f) overlapping and adding the extrapolated vocal tract characteristic signals to the glottal characteristic signal separated at step (d) so as to generate a synthetic speech signal which varies in a desired pitch length; and

(g) wherein the step (f) comprises the further steps of multiplying the signal obtained at the step (e) by the weight function Wh(t), said weight function Wh(t) being as follows;

##EQU4## where n is 0, 1, 2, 3 , , , etc., t is time, Ep_n is an epoch point, Ls_n is a glottal open interval of speech signals, and Lf_n is a glottal closure interval of speech signals; and

(h) overlapping and adding the multiplied signal and glottal characteristic signal to generate a synthetic speech signal.

2. The pitch modification method according to claim 1, wherein the glottal closure interval detected in step (c) is 40-50% in one pitch period from the time of epoch.

3. The pitch modification method according to claim 1, wherein the glottal open interval in step (d) is 40-60% in one pitch period located just before the timing of the glottal closure interval.

4. The improved pitch modification method according to claim 1, wherein step (d) further comprises the steps of:

(d-1) generating a multiplied speech signal by multiplying the speech signal by a weight function for separating the vocal tract and glottal characteristic signal by the speech signal;

(d-2) separating the vocal tract characteristic signal and glottal characteristic signal in said multiplied speech signal; and

(d-3) locating the separated signals in the desired pitch positions.

5. The improved pitch modification method according to claim 1, wherein at step (e) a signal succeeding to the speech signals in the glottal closure interval is linearly extrapolated by using the estimated vocal tract parameter.

6. An improved pitch modification method for producing a pitch modified digital speech signal of an input voiced speech signal of a subject frame of an entire voiced speech signal by glottal closure interval extrapolation, comprising steps of:

(a) converting said input voiced speech into an electric analog speech signal;

(b) converting said electric analog speech signal into a digital speech signal;

(c) detecting a present pitch and an epoch in said input voiced speech signal of the subject frame;

(d) determining a glottal closure interval using said detected present pitch and said epoch

(e) determining if the detected present pitch equals a desired pitch;

(f) if the detected present pitch equals the desired pitch, then shifting into a next frame and repeating steps (a)-(d);

(g) if the detected present pitch does not equal a desired pitch, then separating a vocal tract characteristic signal and a glottal characteristic signal using a weight function Wh(t), said weight function Wh(t) being as follows;

##EQU5## where n 0,1,2,3, . . . etc., t is time, Ep_n is an epoch, point Ls_n is a glottal open interval of speech signals, and Lf_n is a glottal closure interval of speech signals;

(h) determining if the glottal closure interval is smaller than the desired pitch;

(i) if half the present pitch is smaller than the desired pitch, then estimating the vocal tract parameters and extrapolating a linear signal successive to speech signals in the glottal closure interval by using vocal tract parameters;

(j) multiplying the extrapolated linear signal by said weight function for generating a multiplied signal;

(k) overlapping and adding the multiplied signal to a vocal tract and glottal characteristic signal;

(l) determining whether said input voiced speech signal is end of said entire voiced speech signal;

(m) if said input voiced speech signal is the end of said entire voiced speech signal, shifting input voiced speech signal of current frame into a next frame; and

(n) if the input voiced speech signal is not the end of speech signal, repeatedly executing steps (a)-(d).