Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Reexamination Certificate
2000-05-10
2003-02-25
Chawan, Vijay (Department: 2654)
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
C704S230000, C704S225000, C704S244000, C704S205000
Reexamination Certificate
active
06526378
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method and an apparatus for processing a sound signal such as speech or music, which processes the signal so that subjectively bad component included in the sound signal such as quantization noise generated in encoding/decoding process, or sound distortion made by various signal processing such as noise suppression is made subjectively unperceptible.
BACKGROUND ART
The more compressibility is increased in encoding information source such as speech or music, the more quantization noise is generated as a distortion made in the encoding process. Furthermore, the quantization noise becomes warped to cause the reproduced sound to be subjectively unbearable. For example, in case of speech encoding method faithfully expressing a speech signal itself such as PCM (Pulse Code Modulation) and ADPCM (Adaptive Differential Pulse Code Modulation), the quantization noise appears at random and the reproduced sound including such a noise is not so subjectively unpleasant. However, as the compressibility is increased and the encoding method becomes more complex, sometimes there appear a certain spectral characteristic peculiar to the encoding method in the quantization noise, which causes the reproduced sound to become subjectively degraded:. Especially, within a signal period where background noise is dominant, a speech model utilized by the speech encoding method with high compressibility does not match, thus the reproduced sound becomes extremely unpleasant sound.
In another case, on performing a noise suppression such as a spectral subtraction method, there remains an estimated error of noise as a damage in the processed signal. This estimated error has a characteristic being much different from the original signal, which may damage subjective evaluation of the reproduced sound.
Conventional methods to suppress the degradation of the subjective evaluation of the reproduced sound due to the quantization noise or distortion are disclosed in Japanese Unexamined Patent Publications No. HEI 8-130513, No. HEI 8-146998, No. HEI 7-160296, HEI 6-326670, HEI 7-248793, and S. F. Boll, “raction SSP-27, No. 2, pp. 113-120, April 1979) (this document is referred to as “document 1”, hereinafter).
Japanese Unexamined Patent Publication No. HEI 8-130513 aims to improve the quality of the reproduced sound within the background noise period. It is checked whether the period includes only background noise or not. When it is detected to be the period including only background noise, a sound signal is encoded/decoded in an exclusive way to such a period. On decoding the encoded signal within the period including only background noise, the characteristics of a synthetic filter is controlled so as to obtain the perceptually natural reproduced sound.
In Japanese Unexamined Patent Publication No. HEI 8-146998, white noise or previously stored background noise is added to the decoded speech so as to prevent the white noise from turning into harsh grating noise in the reproduced sound due to encoding or decoding.
Japanese Unexamined Patent Publication No. HEI 7-160296 aims to perceptually reduce the quantization noise by postfiltering using a coefficient, which is a filtering coefficient obtained based on an perceptually masking threshold value corresponding to a decoded speech or an index concerning a spectral parameter received by a speech decoding unit.
In a conventional code transmission system where the transmission of the code is suspended during non-speech period for controlling communication power, the decoding side generates and outputs pseudo background noise when the code transmission is suspended. Japanese Unexamined Patent Publication No. HEI 6-326670 aims to reduce an incongruity between an actual background noise included in the speech period and the pseudo background noise generated for the non-speech period. In this method, the pseudo background noise is overlaid onto the sound signal of the speech period as well as the non-speech period.
Japanese Unexamined Patent Publication No. HEI 7-248793 aims to perceptually reduce the distortion sound generated by the noise suppression. First, the encoding side checks whether it is the noise period or the speech period. In the noise period, the noise spectrum is transmitted. In the speech period, the spectrum of speech, in which noise has been suppressed is transmitted. The decoding side generates and outputs a synthetic sound using the received noise spectrum in the noise period. In the speech period, the synthetic sound generated using the received spectrum of speech, in which noise has been suppressed is added to a result of multiplication of the synthetic sound generated using the noise spectrum received in the noise period and overlaying multiplying factor, and the added result is output.
Document
1
aims to perceptually reduce the distortion sound due to the noise suppression by smoothing the amplitude spectrum of the output speech, in which noise has been suppressed with the previous/subsequent period, and further, by suppressing the amplitude only in the background noise period.
As for the above conventional methods, the following problems are to be solved.
In Japanese Unexamined Patent Publication No. HEI 8-130513, there is a problem that a sudden change of the characteristic may happen at a border between the noise period and the speech period because encoding and decoding are completely switched based on the period check result. In particular, if it frequently happens that the noise period is misjudged to be a speech period, the reproduced sound of the noise period, which is to be relatively stable in general, unsteadily changes. This may cause degradation of the reproduced sound of the noise period. When the check result of the noise period is transmitted, information for transmission is required to be added. This information may be mistook on the channel, which may cause another problem, that is, unnecessary degradation. Further, there is another problem that an effective improvement cannot be brought to the reproduced sound in case of specific kind of noise because it is impossible to reduce the quantization noise generated by encoding the sound source only by controlling the characteristic of a synthetic filter.
Japanese Unexamined Patent Publication No. HEI 8-146998 has a problem that a characteristic of the present encoded background noise may lose because a prepared noise is added. In order to make a degraded sound unperceptible, it is required to add a noise with higher level than the degraded sound. This causes another problem that the reproduced background noise becomes loud.
In Japanese Unexamined Patent Publication No. HEI 7-160296, an perceptually masking threshold value is obtained based on a spectral parameter, and a spectral postfiltering is performed based on this threshold value. There is a problem that in case of a background noise with relatively flat spectrum, few components are masked, which may cause no effect to the reproduced sound. Unmasked main component is not much changed, thus there is another problem that a distortion included in the main component may remain unchanged.
In Japanese Unexamined Patent Publication No. HEI 6-326670, pseudo background noise is generated regardless of the actual background noise, which causes a problem that a characteristic of the actual background noise may lose.
In Japanese Unexamined Patent Publication No. HEI 7-248793, encoding and decoding is completely switched according to the period check result, so that when the period is mistook between the noise period and the speech period, the reproduced sound may much degraded. Namely, when a part of the noise period is mistook as the speech period, the quality of the reproduced sound within the noise period discontinuously varies and the reproduced sound becomes unpleasant to hear. On the contrary, when the speech period is mistook as the noise period, the quality of the reproduced sound is generally degraded because speech component may be inserted in the synthetic sound of the noise period generat
Birch & Stewart Kolasch & Birch, LLP
Chawan Vijay
Mitsubishi Denki & Kabushiki Kaisha
LandOfFree
Method and apparatus for processing sound signal does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for processing sound signal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for processing sound signal will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3180496