Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Reexamination Certificate
2000-12-05
2003-04-15
Banks-Harold, Marsha D. (Department: 2654)
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
C704S221000, C704S225000
Reexamination Certificate
active
06549885
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a CELP (Code Excited Linear Prediction) type voice encoding device and a CELP type voice decoding device in a mobile communication system and the like which encodes and transmits a voice signal, and a mobile communication device.
BACKGROUND ART
The CELP type voice encoding device divides a voice into certain frame lengths, linearly predicts the voice in each frame and encodes a prediction residue (activating signal) resulting from the linear prediction for each frame by using an adaptive code vector and a noise code vector constituted of known waveforms. For the adaptive code vector and the noise code vector, as shown in
FIG. 34
, the adaptive code vector and the noise code vector which are stored in an adaptive code book
1
and a noise code book
2
, respectively, are used as they are in some case. As shown in
FIG. 35
, in another case used are the adaptive code vector from the adaptive code book
1
and the noise code vector from the noise code book
2
which is synchronized with a pitch cycle L of the adaptive code book
1
.
FIG. 35
shows a constitution of a noise sound source vector generating portion in the CELP type voice encoding device which is disclosed in publications of Patent Application Laid-open No. Hei 5-19795 and Hei 5-19796. In
FIG. 35
, the adaptive code vector is selected from the adaptive code book
1
, while the pitch cycle L is emitted. The noise code vector selected from the noise code book
2
is made periodic by a periodic unit
3
using the pitch cycle L. To make periodic the noise code vector, the vector is cut by the pitch cycle from its top and repeatedly connected plural times until a sub-frame length is reached.
However, in the aforementioned conventional CELP type voice encoding device in which the noise code vector is pitch-cycled, after an adaptive code vector component is removed, a residual pitch cycle component is removed by making periodic the noise code vector in the pitch cycle. Therefore, phase information which exists in one pitch waveform, that is, the information representing where a pitch pulse peak exists is not positively used. Therefore, enhancement of voice quality has been restricted.
The present invention has been developed to solve the conventional problem, and an object thereof is to provide a voice encoding device which can further enhance a voice quality.
DISCLOSURE OF THE INVENTION
To attain the aforementioned object, in the invention, by emphasizing an amplitude of a noise code vector which corresponds to a pitch peak position of an adaptive code vector, phase information existing in one pitch waveform is used to enhance a sound quality.
Also in the invention, by using the noise code vector which is restricted only in the vicinity of the pitch peak of the adaptive code vector, even when a small number of bits are allocated to the noise code vector, a deterioration in sound quality is minimized.
Further in the invention, by using the pitch peak position and a pitch cycle of the adaptive code vector to restrict a pulse position search range, even when there are a small number of bits indicative of pulse positions, the search range is narrowed while minimizing the deterioration in sound quality.
Also in the invention, when the pitch peak position and pitch cycle of the adaptive code vector are used to restrict the pulse position search range, especially by finely setting a pulse position searching precision in one or two pitch waveform, sound quality is enhanced in a voiced portion of a voice with a short pitch cycle.
Also in the invention, by varying the number of pulse sound source pulses with a pitch cycle value, sound quality is enhanced.
Also in the invention, by determining a pulse amplitude in the vicinity of the pitch peak position of the adaptive code vector and the other portions before searching the pulse sound source, sound quality is enhanced.
Also in the invention, since a pitch gain is quantized in multiple stages and a first stage of information quantization is performed immediately after an adaptive code book is searched, the first-stage quantized information of the pitch gain can be used as mode information for switching a noise code book. Encoding efficiency is thus enhanced.
Also in the invention, by using quantized pitch cycle information or quantized pitch gain information in the immediately previous sub-frame or the present sub-frame, a control is performed to switch search positions of the pulse sound source. Therefore, voice quality is enhanced.
Also in the invention, a phase continuity between sub-frames is determined backward. Only to the sub-frame whose phase is determined to be continuous, a phase adaptation process is applied. Thereby, without increasing the quantity of information to be transmitted, the phase adaptation process is switched. Thus, voice quality is enhanced. Additionally, when the phase adaptation process is not performed, by using a fixed code book, an error in transmission line can be effectively prevented from being propagated.
Also in the invention, it is determined by a degree of centralization of signal power to the vicinity of the pitch peak position in the adaptive code vector whether or not the phase adaptation process is to be applied. Thereby, without increasing the quantity of information to be transmitted, the phase adaptation process is switched. Voice quality is thus enhanced. Additionally, when the phase adaptation process is not performed, by using the fixed code book, a transmission line error can be effectively prevented from being propagated.
Also according to the invention, in the CELP type voice encoding device in which sound source pulses are searched in positions relative to the pitch peak position, the pulse positions are indexed in order from the top of the sub-frame. Thereby, the influence of the transmission line error which occurs in some frame is prevented from being propagated to subsequent frames which have no transmission line error.
Also according to the invention, in the CELP type voice encoding device in which sound source pulses are searched in the positions relative to the pitch peak position, the pulse positions are indexed in order from the top of the sub-frame. Additionally, different pulses having the same index are numbered in order from the top of the sub-frame. Thereby, the influence of the transmission line error which occurs in some frame is prevented from being propagated to the subsequent frames which have no transmission line error.
Also according to the invention, in the CELP type voice encoding device in which sound source pulses are searched in the positions relative to the pitch peak position, all the pulse search positions are not represented by the relative positions. Only a part of the vicinity of the pitch peak is represented by the relative positions, while the remaining part is set in predetermined fixed positions. Thereby, the influence of the transmission line error which occurs in some frame is prevented from being propagated to the subsequent frames which have no transmission line error.
Also in the invention, when the pitch peak position is obtained, instead of searching all object signals for the pitch peak position, there is provided a means for searching signals in the cut pitch cycle length for the pitch peak position. Thereby, the top pitch peak position can be extracted more precisely.
Also according to the invention, in a portion in which the pitch cycle is continuous between the sub-frames, that is, a portion which is supposed to be a voiced stationary portion, the pitch peak position in the immediately previous sub-frame, the pitch cycle in the immediately previous sub-frame and the pitch cycle in the present sub-frame are used to predict the pitch peak position in the present sub-frame. Based on the predicted pitch peak position, an existence range of the pitch peak position in the present sub-frame is restricted. Thereby, the pitch peak position can be extracted in such a manner that the phase in the voiced stationary portion is prevented from being
Ehara Hiroyuki
Morii Toshiyuki
Banks-Harold Marsha D.
Lerner Martin
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
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