Data processing: speech signal processing – linguistics – language – Speech signal processing
Reexamination Certificate
2000-05-15
2003-05-27
{haeck over (S)}mits, T{overscore (a)}livaldis Ivars (Department: 2654)
Data processing: speech signal processing, linguistics, language
Speech signal processing
C704S200100, C704S205000
Reexamination Certificate
active
06571207
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for processing the phase information of an acoustic signal and a method thereof, and more particularly, to a device for processing the phase information of an acoustic signal, by which important phase components are discriminated in consideration of human auditory recognition characteristics, and a method thereof.
2. Description of the Related Art
Research into auditory psychophysics due to a change in the phase of an acoustic signal is in progress, but useful results have not yet been obtained in large numbers. The research results into auditory psychophysics due to a change in the phase of acoustic signals are disclosed by E. Zwicker and H. Fastl, [“Psychoacoustics-Facts and Models”, Springer-Verlag, 2
nd
Eds, 1999], and B. C. J. Moore, [“Introduction to the Psychology of Hearing”, Academic Press, 4
th
Eds., 1997]. According to these documents, the cochlea of the internal ear among hearing organs can be modeled as a filter bank. The filter bank includes band pass filters, and the passband of each filter can be estimated when the central frequency of the filter is given. Signal processing within a human ear has been known as multi-channel signal processing preformed in units of each critical band of the filter.
When a phase change in a signal is considered from this standpoint, a local phase change denotes a change in the relative phase relationship between signal components which exist within the same critical band (i.e., within the same channel). A global phase change denotes that the phase relationship between channels varies while the relative phase relationship between signal components within the same critical band is being kept. The human ear is dull to global phase changes and somewhat sensitive to local phase changes, which is not completely theorized but known in relation to auditory psychophysics with respect to phase. This is disclosed by R. D. Patterson, [“A Pulse Ribbon Model of Monaural Phase Perception”, J. Acoust. Soc. Am., Vol. 82, No. 5, pp. 1560-1586,1987]; and M. R. Schroeder, [“New Results Concerning Monaural Phase Sensitivity”, J.Acoust. Soc. Am, Vol. 31, p.1579, 1959].
Also, phase information processing in a harmonic speech system is disclosed by R. J. MacAulary and T. F. Quatieri, “Sinusoidal Coding in Speech Coding and Synthesis”, W. B. Kleijn and K. K. Palivwal Eds, Elsevier, pp. 121-173, 1998; J. S. Marques and L. B. Almeida, “Sinusoidal Modeling of Voiced and Unvoiced Speech”, in Proc. ICASSP, pp. 203-206, 1983; and J. S. Marques, L. B. Almeida, and J. M. Tribolet, “Harmonic coding at 4.8 kb/s”, in Proc. ICASSP, pp. 17-20, 1990. According to these documents, a harmonic speech coding system can be used to express the excitation signal of speech using the following Equation 1:
e
(
n
)
=
∑
k
=
1
K
A
k
cos
(
k
ω
0
n
+
θ
k
)
(
1
)
wherein &ohgr;
0
denotes a fundamental frequency, A
k
denotes the spectral magnitude of harmonics, and &thgr;
k
denotes the phase of harmonics. The excitation signal is used as the input to a filter which has been modeled by the spectral envelope of speech, to thereby finally obtain an acoustic signal. Thus, in a speech coding system, spectrum envelope filter coefficients, the spectral magnitude A
k
, the fundamental frequency &ohgr;
0
, and the phase of harmonics (&thgr;
k
) are quantized and transmitted, and acoustic signals are synthesized using the received parameters. In present harmonic speech coding systems, the spectrum phase information &thgr;
k
is relatively neglected compared to the spectral magnitude information A
k
of a signal, and a method in which a transmission system does not send the phase information of an acoustic signal, but a reception system applies an arbitrary phase using the condition that the phase of an acoustic signal continuously changes, is generally used.
However, an acoustic signal synthesized by the conventional method does not provide a satisfactory quality of sound. Also, when phase information is completely coded to solve this problem, the amount of information increases too much.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide an acoustic signal phase information processing device, in which important phase components are discriminated in consideration of human auditory characteristics to selectively code or synthesize the phase components of an acoustic signal.
Another objective of the present invention is to provide an acoustic signal phase information processing method performed by the above device.
To achieve the first objective, there is provided a device for processing the phase information of a digital speech signal which is expressed as a discrete sum of periodic signals having different frequency components, according to an aspect of the present invention. This device includes: a critical bandwidth calculator for calculating the critical bandwidth of each frequency according to the bandwidth characteristics of a human's auditory filter; a frequency range setting unit for setting the frequency ranges of local phase changes using critical bandwidths corrected by multiplying the critical bandwidths by a predetermined scaling coefficient; and a phase significance discriminator for checking whether frequency components adjacent to each frequency are within the frequency range corresponding to the frequency, and discriminating whether the phase of a signal having the frequency component is significant in terms of auditory characteristics.
Preferably, the device further includes an acoustic signal transformer for transforming an acoustic signal into the discrete sum of periodic signals having different frequency components. Also, it is preferable that the scaling coefficient is smaller than 1. Preferably, the phase significance discriminator obtains an assembly of frequencies having phases that are significant in terms of auditory characteristics.
To achieve the first objective, a device for processing the phase components of an acoustic signal, according to another aspect of the present invention, includes: an acoustic signal transformer for transforming an acoustic signal into
s
(
n
)
=
∑
l
=
1
L
A
l
cos
(
ω
l
n
+
θ
l
)
,
wherein L is an integer greater than 1, A
1
, &ohgr;
l
, and &thgr;
I
denote the spectral magnitude, frequency, and phase of an I-th periodic signal, respectively, and &ohgr;
1
<&ohgr;
2
<. . . <&ohgr;
L
; a critical bandwidth calculator for calculating the critical bandwidth of each frequency according to the bandwidth characteristics of a human's auditory filter; a frequency range setting unit for obtaining critical bandwidths &ohgr;
L,UB
and &ohgr;
l,LB
corrected by multiplying the critical bandwidths by a predetermined scaling coefficient, and setting a frequency set of a channel satisfying the condition of &ohgr;
l,LB
≦&ohgr;≦&ohgr;
l
with the frequency &ohgr;
l
set as an upper bound, to be C(&ohgr;
l
,1), and setting a frequency set of a channel satisfying the condition of &ohgr;
l
≦&ohgr;≦
I,UB
with the frequency &ohgr;
I
set as a lower bound, to be C(&ohgr;
l
,2); and a phase significance discriminator for discriminating whether the conditions of &ohgr;
I−1
∉C(&ohgr;
l
,1) and &ohgr;
l+1
∉C(&ohgr;
l
,2) are satisfied with respect to &ohgr;
l
, and outputting significance data representing that the phase &thgr;
I
of the frequency &ohgr;
l
is not significant in terms of auditory characteristics, if the conditions are satisfied, and otherwise, outputting significance data representing that the phase &thgr;
I
of the frequency &ohgr;
l
is significant in terms of auditory characteristics.
To achieve the second objective, a method of processing the phase components of an acoustic signal, according to an aspect of the present invention includes: (a) expressing an acoustic signal as a discrete sum of periodic sig
Azad Abul K.
Burns Doane Swecker & Mathis L.L.P.
Samsung Electronics Co,. Ltd.
{haeck over (S)}mits T{overscore (a)}livaldis Ivars
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