Data processing: speech signal processing – linguistics – language – Speech signal processing – Synthesis
Reexamination Certificate
1999-10-14
2003-03-25
Banks-Harold, Marsha D. (Department: 2654)
Data processing: speech signal processing, linguistics, language
Speech signal processing
Synthesis
C704S223000
Reexamination Certificate
active
06539355
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a signal band expanding method and apparatus and signal synthesis method and apparatus in which speech signals of a narrow frequency range, transmitted by communication or broadcasting or stored in a medium, or parameters making up the signals, are transmitted over a transmission path or directly recorded on the medium, so as to be used on the reception or reproducing side for estimating the broad-band speech signals on the receiving or reproducing side, and which may be used with advantage especially in a portable telephone terminal having the band expanding function.
2. Description of the Related Art
The bandwidth of the telephone network is narrow such as 300 to 3400 such that limitations are imposed on the frequency band of speech signals sent over the telephone network. Therefore, the sound quality of the conventional analog telephone network cannot be said to be optimum. The digital portable telephone also is not satisfactory in sound quality.
However, since the standard of the transmission path is fixed, it is difficult to enlarge its bandwidth. Thus, a variety of systems are now proposed for predicting signal components outside the band on the receiving side to generate broad-band signals.
In particular, in systems exploiting the vector sum excited linear prediction (VSELP) coding or pitch synchronization innovation—code excited linear prediction (PSI-CELP), which are the speech codec system for car/portable telephone in Japan, attention is directed to LPC synthesis, both the linear prediction coefficients &agr; and the excitation source are enlarged in the frequency range and LPC synthesis is made by &agr; and the excitation source of the broad bandwidth.
However, the broad band-speech, thus obtained, suffers from distortion. Therefore, in the frequency component contained in the original speech, the original speech is naturally of higher quality, and hence these components contained in the synthesized broad-band speech are filtered off and summed to the original speech.
For combatting the overflow in the digital signal processing, there are known methods of clipping the digital signal to a maximum value or of adjusting the gain of the entire signal to prevent signal overflow.
However, if overflow occurs in the process of addition of main signals and sub-signals, and it is desired not to change the main signal even if the sub-signal is eliminated in its entirety, these overflow combatting measures are not optimum.
There is also known a technique in which the speech of the vector sum excited linear prediction (VSELP) coding and pitch synchronization innovation—code excited linear prediction (PSI-CELP) coding system, as the speech codec of the car/portable telephone in the personal digital cellular (PDC) system, having the frequency bandwidth of 300 to 3400 Hz, is enlarged in bandwidth to approximately 300 to 6000 Hz by estimating the signal components outside the band on the receiving side. In this technique, the signals outside the transmission bandwidth is synthesized and summed to the narrow band signals corresponding to the original speech signals.
Among transmitted narrrow band parameters, there are a linear prediction coefficient &agr;, a reflection coefficient k and a line spectrum pair (LSP). These represent the speech spectrum envelope, with the number of orders of the coefficients corresponding to peaks of the spectrum. In the PDC system, up to the tenth order coefficients are transmitted, in consideration that the number of formants in the human voice up to approximately 3400 Hz is on the order of five.
One of a wide variety of possible prediction methods for the wide range parameter representing the wide band formant exploits vector quantization. In this method, a number of vectors corresponding to the number of orders of the broad band parameters are prepared by previous learning and, on inputting of the narrow band parameter, a suitable broad band vector is selected from these parameters as the broad band parameter.
It has now been found that, in the broad band speech, thus synthesized, there exists a marked difference in personal appreciation of the sound quality and hence it is preferred not to fix the gain of the high range component synthesized by prediction. Similarly, the high range component not less than 6 kHz, for which the general preference is moderate suppression, also is preferably not fixed.
It is therefore an object of the first subject-matter of the present invention to provide a bandwidth expanding method and apparatus in which frequency characteristics of high-frequency components can be adjusted to the liking of users.
On the other hand, in the above-described bandwidth expansion technique, overflow by addition is eventually produced. However, the main signal needs to be the original signal at any rate, while the component outside the transmission band is not needed at the cost of generation of extraneous sound ascribable to overflow.
It is therefore not desirable to clip the signal at the maximum value to produce extraneous sound or to adjust the entire signal to produce perceptible power variations, and hence an alternative overflow combatting technique is desired.
It is therefore an object of the second subject-matter of the present invention to provide a signal processing method and apparatus for suppressing overflow by adjusting only the signals of the subsidiary system.
It is also an object of the second subject-matter of the present invention to provide a bandwidth expanding method and apparatus in which it is possible to suppress overflow and to expand the bandwidth without changing the low range signals to improve spontaneity in hearing.
In addition, in estimating and synthesizing the broad-band speech from the narrow band parameters, transmitted as described above, the number of formants naturally is larger than that for the narrow bands, that is five.
The increased number of formants is not meritorious since comparison is then made of finer components of the spectrum envelope to depart from the inherent intention of roughly estimating the broad-band spectrum envelope.
It is therefore an object of the third subject-matter of the present invention to provide a speech band expanding method and apparatus and speech synthesis method and apparatus in which the number of broad-band formants can be diminished, importance can be attached to the rough structure of the spectrum, the broad-band speech can be improved in quality and in which the processing volume required in the memory capacity and codebook searching can be saved.
SUMMARY OF THE INVENTION
In connection with the first subject-matter, the present invention provides a bandwidth expanding method for expanding a bandwidth by estimating, from narrow-band signals or from parameters allowing for synthesizing the narrow-band signals, outside-band components, and by adding the outside-band components to the narrow-band signals, wherein frequency characteristics of the outside-band components are first adjusted by pre-set alterable parameter values and subsequently the outside-band components are added to the narrow-band signals.
In connection with the first subject-matter, the present invention provides a bandwidth expanding apparatus for expanding the bandwidth by estimating, from narrow-band signals or from parameters allowing for synthesizing the narrow-band signals, outside-band components, and by adding the outside-band components to the narrow-band signals, wherein the apparatus includes frequency characteristics adjustment means for adjusting frequency characteristics of the outside-band components by pre-set alterable parameter values, and addition means for adding the outside-band components, the frequency characteristics of which have been adjusted by the frequency characteristics adjustment means, to the narrow-band signals.
In connection with the first subject-matter, the present invention provides a bandwidth expanding apparatus for expanding the bandwidth by estimating, from narrow-band s
Nishiguchi Masayuki
Omori Shiro
Banks-Harold Marsha D.
Maioli Jay H.
Sony Corporation
Storm Donald L.
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