Pitch determination apparatus and method using...

Details Pitch determination apparatus and method using... Pitch determination apparatus and method using...

1999-01-07

2001-03-27

Hudspeth, David (Department: 2741)

Data processing: speech signal processing, linguistics, language

Speech signal processing

For storage or transmission

C704S263000, C704S267000, C704S268000, C704S217000, C704S216000

Reexamination Certificate

active

06208958

ABSTRACT:

This application claims priority under 35 U.S.C. §§119 and/or 365 to 98-13665 filed in Korea on Apr. 16, 1998; the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to speech signal processing, and more particularly, to a pitch determination apparatus and method which is used in a voice coder of a low bit rate, a voice recognition apparatus, etc.
2. Description of the Related Art
A pitch is generated by periodical characteristics of opening and closing of a vocal cord in the respect of the characteristics of voice production of human being. This pitch is an important parameter which is used upon voice modeling. The pitch is usually applied to, for example, a voice coder (or a vocoder or a voice codec), voice recognition, voice transformation, etc.
In a case of a low bit rate voice decoder, when an error is generated upon pitch determination, the quality of speech communication is significantly deteriorated. Thus, in these application fields, it is very important to select an accurate pitch determination method.
Generally, a pitch determination error can be a pitch doubling, a pitch halving, or a first formant error. In the pitch doubling, an original pitch T is erroneously determined to be 2T, 3T, 4T, . . . In the pitch halving, an original pitch T is erroneously determined to be T/2, T/4, T/8, . . . The first formant error is generated when the autocorrelation of a first formant is greater than the correlation value of a pitch.
FIG. 1
shows a widely-used conventional pitch determination method using autocorrelation at a time axis.
However, in this conventional pitch determination method, an error due to pitch doubling occurs frequently.
For example, when an input voice is the same as
FIG. 5A
, an autocorrelation value is the same as FIG.
5
B. When an original voice pitch is
31
, the autocorrelation method provokes an error upon pitch determination since correlation values of candidate pitches
31
,
62
and
93
are large.
Accordingly, the conventional pitch determination method using the autocorrelation has a high pitch determination error rate, thus significantly degrading the tone quality of a voice coder. Particularly, when background noise is mixed in an input voice, the tone quality is more deteriorated due to a pitch determination error.
SUMMARY OF THE INVENTION
To solve the above problem, it is an objective of the present invention to provide a pitch determination apparatus and method which uses spectro-temporal autocorrelation to prevent pitch determination errors.
Accordingly, to achieve the above objective, there is provided a pitch determination apparatus using spectro-temporal autocorrelation, comprising: a formant bandwidth extension unit for extending a formant bandwidth to reduce the influence of a first formant with respect to an input voice; a temporal autocorrelation calculation unit for calculating an autocorrelation value of a time axial voice within a candidate pitch range with respect to a time axial speech signal output from the formant bandwidth extension unit; a spectral autocorrelation calculation unit for transforming the time axial speech signal output from the formant bandwidth extension unit into a frequency axial signal, and calculating an autocorrelation value between frequency axis amplitude spectrums within the candidate pitch range; an autocorrelation value synthesis unit for summing the autocorrelation values obtained by the temporal and spectral autocorrelation calculation units and obtaining a spectro-temporal autocorrelation value; and a pitch determination unit for determining a pitch having a maximum spectro-temporal autocorrelation value as a final pitch.
To achieve the above objective, there is provided a method of determining a pitch with respect to an input speech signal using spectro-temporal autocorrelation, comprising the steps of: extending a formant bandwidth to reduce an influence of a first formant with respect to the input speech signal; calculating temporal autocorrelation values with respect to a candidate pitch from a formant-extended speech signal output from the formant bandwidth extension step; calculating spectral autocorrelation values with respect to the candidate pitch from the formant-extended speech signal output from the formant bandwidth extension step; obtaining spectro-temporal autocorrelation values with respect to the candidate pitch using the temporal and spectral autocorrelation values obtained by the above steps; and determining a candidate pitch having a maximum spectro-temporal autocorrelation value as a pitch.


REFERENCES:
patent: 5365592 (1994-11-01), Horner et al.
patent: 5619004 (1997-04-01), Dame
patent: 5799271 (1998-08-01), Byun et al.
patent: 5822732 (1998-10-01), Tasaki
patent: 5911128 (1999-06-01), DeJaco
patent: 6041297 (2000-03-01), Goldberg
patent: 6047254 (2000-04-01), Ireton et al.

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