Signal processing apparatus and mobile radio communication terminal Number:7,058,574 from the United States Patent and Trademark Office (PTO) owispatent

Title: Signal processing apparatus and mobile radio communication terminal

Abstract: In a signal processing apparatus, a speech coder includes, as three sections for coding speech data by different algorithm, an Algorithm-A coding section, an Algorithm-B coding section and an Algorithm-C coding section. A noise suppressor includes, as three sections for suppressing background noise by different algorithm, an Algorithm-X noise suppress section, an Algorithm-Y noise suppress section and an Algorithm-Z noise suppress section. A suppress algorithm switching control section controls switching on the basis of information from a coding algorithm switching control section such that an optimal one of the noise suppress sections may function in association with the coding section activated in the speech coder.

Patent Number: 7,058,574 Issued on 06/06/2006 to Taniguchi,   et al.

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Inventors:	Taniguchi; Takayuki (Kawasaki, JP); Tsukahara; Yuriko (Kawasaki, JP); Miseki; Kimio (Yokohama, JP)
Assignee:	Kabushiki Kaisha Toshiba (Kawasaki, JP)
Appl. No.:	000268
Filed:	December 1, 2004

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Foreign Application Priority Data

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May 10, 2000 [JP]			2000-137181

Current U.S. Class:	704/233
Current International Class:	G10L 19/00 (20060101)

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References Cited [Referenced By]

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U.S. Patent Documents

	5659622		August 1997		Ashley
	5812970		September 1998		Chan et al.
	6122384		September 2000		Mauro
	6141639		October 2000		Thyssen
	6496798		December 2002		Huang et al.
	6604070		August 2003		Gao et al.
	6810273		October 2004		Mattila et al.
	6925435		August 2005		Gao
	2001/0001853		May 2001		Mauro et al.

Foreign Patent Documents

	WO 99/01972		Jan., 1999		WO
	WO 00/11650		Mar., 2000		WO

Other References

Patent Abstracts of Japan, JP 5-300209, Nov. 12, 1993. cited by other.

Primary Examiner: McFadden; Susan
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.

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Parent Case Text

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CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent document is a continuation of U.S. application Ser. No. 09/852,235, filed on May 10, 2001, now abandoned, and in turn claims the benefit of priority from the prior Japanese Patent Application No. 2000-137181, filed May 10, 2000, the entire contents of each of which are incorporated herein by reference.

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Claims

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What is claimed is:

1. A signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics for suppressing background noise contained in a speech signal, where a number of the noise suppression characteristics is Q (Q: a positive integer); a speech encoder having a plurality of different speech coding algorithms for encoding an output signal from the noise suppressor, where a number of the speech coding algorithms is P (P: positive integer and P.gtoreq.Q>1); means for selecting one of the plurality of noise suppression characteristics and one of the plurality of speech coding algorithms based upon a select command; and control means for activating the noise suppressor with the selected noise suppression characteristic and the speech encoder with the selected speech coding algorithm, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

2. The signal processing apparatus according to claim 1, wherein one of the speech coding algorithms is the AMR standard or the EVRC standard.

3. A signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics for suppressing background noise contained in a speech signal, where a number of the noise suppression characteristics is Q (Q: a positive integer); a speech encoder having a plurality of different speech coding rates for encoding an output signal from the noise suppressor, where a number of the speech coding rates is R (R: positive integer and R.gtoreq.Q>1); means for selecting one of the plurality of noise suppression characteristics and one of the plurality of speech coding rates based upon a select command; and control means for activating the noise suppressor with the selected noise suppression characteristic and the speech encoder with the selected speech coding rate, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

4. A signal processing apparatus comprising: a parameter table configured to store a plurality of parameter sets for characterizing a noise suppressor, where a number of the parameter sets is S (S: a positive integer); a noise suppressor, whose noise suppression characteristic is varied in accordance with the parameter set, configured to suppress background noise contained in a speech signal; a speech encoder having a plurality of different speech coding algorithms for encoding an output signal from the noise suppressor, where a number of the speech coding algorithms is P (P: positive integer and P.gtoreq.S>1); means for selecting one of the plurality of parameter sets and one of the plurality of speech coding algorithms based upon a select command; and control means for activating the noise suppressor with the noise suppression characteristic in accordance with the selected parameter set and the speech encoder with the selected speech coding algorithm, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

5. The signal processing apparatus according to claim 4, wherein one of the speech coding algorithms is the AMR standard or the EVRC standard.

6. A signal processing apparatus comprising: a parameter table configured to store a plurality of parameter sets for characterizing a noise suppressor, where a number of the parameter sets is S (S: a positive integer); a noise suppressor, whose noise suppression characteristic is varied in accordance with the parameter set, configured to suppress background noise contained in a speech signal; a speech encoder having a plurality of different speech coding rates for encoding an output signal from the noise suppressor, where a number of the speech coding rates is R (R: positive integer and R.gtoreq.S>1); means for selecting one of the plurality of parameter sets and one of the plurality of speech coding rates based upon a select command; and control means for activating the noise suppressor with the noise suppression characteristic in accordance with the selected parameter set and the speech encoder with the selected speech coding rate, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

7. A signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression algorithms for suppressing background noise contained in a speech signal, where a number of the noise suppression algorithms is Q (Q: a positive integer); a speech encoder having a plurality of different speech coding algorithms for encoding an output signal from the noise suppressor, where a number of the speech coding algorithms is P (P: positive integer and P.gtoreq.Q>1); means for selecting one of the plurality of noise suppression algorithms and one of the plurality of speech coding algorithms based upon a select command; and control means for activating the noise suppressor with the selected noise suppression algorithm and the speech encoder with the selected speech coding algorithm, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

8. The signal processing apparatus according to claim 7, wherein one of the speech coding algorithms is the AMR standard or the EVRC standard.

9. A signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression algorithms for suppressing background noise contained in a speech signal, where a number of the noise suppression algorithms is Q (Q: a positive integer); a speech encoder having a plurality of different speech coding rates for encoding an output signal from the noise suppressor, where a number of the speech coding rates is R (R: positive integer and R.gtoreq.Q>1); means for selecting one of the plurality of noise suppression algorithms and one of the plurality of speech coding rates based upon a select command; and control means for activating the noise suppressor with the selected noise suppression algorithm and the speech encoder with the selected speech coding rate, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

10. A mobile communication terminal having a signal processor, the signal processor comprising: a microphone configured to capture a speech signal; a noise suppressor having a plurality of different noise suppression characteristics for suppressing background noise contained in the speech signal, where a number of the noise suppression characteristics is Q (Q: a positive integer); a speech encoder having a plurality of different speech coding algorithms for encoding an output signal from the noise suppressor, where a number of the speech coding algorithms is P (P: positive integer and P.gtoreq.Q>1); means for selecting one of the plurality of noise suppression characteristics and one of the plurality of speech coding algorithms based upon a select command; and control means for activating the noise suppressor with the selected noise suppression characteristic and the speech encoder with the selected speech coding algorithm, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

11. A mobile communication comprising: a signal processor, the signal processor comprising: a microphone configured to capture a speech signal; a noise suppressor having a plurality of different noise suppression characteristics for suppressing background noise contained in the speech signal, where a number of the noise suppression characteristics is Q (Q: a positive integer); a speech encoder having a plurality of different speech coding rates for encoding an output signal from the noise suppressor, where a number of the speech coding rates is R (R: positive integer and R.gtoreq.Q>1); means for selecting one of the plurality of noise suppression characteristics and one of the plurality of speech coding rates based upon a select command; and control means for activating the noise suppressor with the selected noise suppression characteristic and the speech encoder with the selected speech coding rate, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

12. A mobile communication terminal comprising: a signal processor, the signal processor comprising: a microphone configured to capture a speech signal; a parameter table configured to store a plurality of parameter sets for characterizing a noise suppressor, where a number of the parameter sets is S (S: a positive integer); a noise suppressor, whose noise suppression characteristic is varied in accordance with the parameter set, configured to suppress background noise contained in the speech signal; a speech encoder having a plurality of different speech coding algorithms for encoding an output signal from the noise suppressor, where a number of the speech coding algorithms is P (P: positive integer and P.gtoreq.S>1); means for selecting one of the plurality of parameter sets and one of the plurality of speech coding algorithms based upon a select command; and control means for activating the noise suppressor with the noise suppression characteristic in accordance with the selected parameter set and the speech encoder with the selected speech coding algorithm, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

13. The mobile communication terminal according to claim 12, wherein one of the speech coding algorithms is the AMR standard or the EVRC standard.

14. A mobile communication terminal comprising: a signal processor, the signal processor comprising: a microphone configured to capture a speech signal; a parameter table configured to store a plurality of parameter sets for characterizing a noise suppressor, where a number of the parameter sets is S (S: a positive integer); a noise suppressor, whose noise suppression characteristic is varied in accordance with the parameter set, configured to suppress background noise contained in the speech signal; a speech encoder having a plurality of different speech coding rates for encoding an output signal from the noise suppressor, where a number of the speech coding rates is R (R: positive integer and R.gtoreq.S>1); means for selecting one of the plurality of parameter sets and one of the plurality of speech coding rates based upon a select command; and control means for activating the noise suppressor with the noise suppression characteristic in accordance with the selected parameter set and the speech encoder with the selected speech coding rate, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

15. A mobile communication terminal comprising: a signal processor, the signal processor comprising: a microphone configured to capture a speech signal; a noise suppressor having a plurality of different noise suppression algorithms for suppressing background noise contained in the speech signal, where a number of the noise suppression algorithms is Q (Q: a positive integer); a speech encoder having a plurality of different speech coding algorithms for encoding an output signal from the noise suppressor, where a number of the speech coding algorithms is P (P: positive integer and P.gtoreq.Q>1); means for selecting one of the plurality of noise suppression algorithms and one of the plurality of speech coding algorithms based upon a select command; and control means for activating the noise suppressor with the selected noise suppression algorithm and the speech encoder with the selected speech coding algorithm, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

16. The mobile communication terminal according to claim 15, wherein one of the speech coding algorithms is the AMR standard or the EVRC standard.

17. A mobile communication terminal comprising: a signal processor, the signal processor comprising: a microphone configured to capture a speech signal; a noise suppressor having a plurality of different noise suppression algorithms for suppressing background noise contained in the speech signal, where a number of the noise suppression algorithms is Q (Q: a positive integer); a speech encoder having a plurality of different speech coding rates for encoding an output signal from the noise suppressor, where a number of the speech coding rates is R (R: positive integer and R.gtoreq.Q>1); means for selecting one of the plurality of noise suppression algorithms and one of the plurality of speech coding rates based upon a select command; and control means for activating the noise suppressor with the selected noise suppression algorithm and the speech encoder with the selected speech coding rate, wherein the speech signal is encoded by using the noise suppressor and the speech encoder activated by the control means.

18. The mobile communication terminal according to claim 10, wherein one of the speech coding algorithms is the AMR standard or the EVRC standard.

19. A signal processing apparatus comprising: a plurality of noise suppressors; a plurality of speech encoders; and means for selecting one of the plurality of noise suppressors and one of the plurality of speech encoders, wherein a background noise contained in an input speech signal is suppressed by using the selected noise suppressor and an output signal from the noise suppressor is encoded using the selected speech encoder.

20. The signal processing apparatus according to claim 19, wherein at least two of the plurality of the noise suppressors have noise suppression characteristics different from each other and at least two of the plurality of the speech encoders have speech coding algorithms different from each other.

21. A mobile communication terminal comprising: a signal processor, the signal processor comprising: a microphone configured to capture a speech signal; a plurality of noise suppressors; a plurality of speech encoders; and means for selecting one of the plurality of noise suppressors and one of the plurality of speech encoders, wherein a background noise contained in the speech signal is suppressed by using the selected noise suppressor and an output signal from the noise suppressor is encoded using the selected speech encoder.

22. The mobile communication terminal according to claim 21, wherein at least two of the plurality of the noise suppressors have noise suppression characteristics different from each other and at least two of the plurality of the speech encoders have speech coding algorithms different from each other.

23. A signal processing apparatus comprising: a plurality of noise suppressor programs; a plurality of speech encoder programs; means for selecting one of the plurality of noise suppressor programs and one of the plurality of speech encoder programs; means for suppressing a background noise contained in a speech signal by using the selected noise suppressor program; and means for encoding an output signal from the noise suppression means by using the selected speech encoder program.

24. A mobile communication terminal comprising: a signal processor, the signal processor comprising: a microphone configured to capture a speech signal; a plurality of noise suppressor programs; a plurality of speech encoder programs; means for selecting one of the plurality of noise suppressor programs and one of the plurality of speech encoder programs; means for suppressing a background noise contained in a speech signal by using the selected noise suppressor program; and means for encoding an output signal from the noise suppression means by using the selected speech encoder program.

25. A signal processing apparatus comprising: a plurality of speech decoders; a plurality of noise suppressors; and means for selecting one of the plurality of speech decoders and one of the plurality of noise suppressors, wherein a speech signal is decoded by using the selected speech decoder and a background noise contained in the speech signal is suppressed by using the selected noise suppressor.

26. A signal processing apparatus comprising: a plurality of speech decoder programs; a plurality of noise suppressor programs; means for selecting one of the plurality of speech decoder programs and one of the plurality of noise suppressor programs; means for decoding a speech signal by using the selected speech decoder program; and means for suppressing a background noise contained in the speech signal by using the selected noise suppressor program.

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Description

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BACKGROUND OF THE INVENTION

The present invention relates to a noise suppressor for reducing noise contained in transmitted/received speech signal, which is used in radio communication apparatuses of various digital communication methods, including a digital mobile phone system.

A telephone service using speech communication is known as a basic service of mobile communication. A mobile telephone system first began with an analog method, but now a digital method is prevailing.

In the digital method, an A/D converter is needed to convert analog speech signals to digital signals. However, simple A/D conversion requires a coding rate of about 100 kbps. Considering limited radio wave resources, it is necessary to compress the digital signals to 1/10 to 1/20. To meet the demand, a high-efficiency speech coding method, generally called speech compression, is employed and it is embodied as a speech CODEC.

In current mobile communications, a speech CODEC with a coding rate of about 3.5 kbps to 32 kbps is used. In the low-rate CODEC, the coding rate is decreased by utilizing the characteristics of speech signals as much as possible. As a result, even if an adequate quality of speech is obtained, the reproducibility and quality of "sound" other than speech tend to deteriorate.

A low-rate speech CODEC is used as an application in mobile phones which are often used outdoors. In some cases, mobile phones are used in an environment with large background noise.

If background noise is input to the low-rate speech CODEC which is designed mainly for "speech", the speech quality will vary. The clearness and quality of speech will deteriorate in the environment with background noise.

As techniques for solving this problem, attention has recently been paid to noise suppressors (or noise cancelers) which are designed to suppress background noise taken in through microphones and to deliver only speech to the speech CODEC.

For example, a noise canceler is described in the chapter "Half-Rate Speech CODEC" in the "Personal Digital Cellular Telecommunication System RCR STD-27" published by Association of Radio Industries and Businesses (ARIB) in Japan.

New speech CODECs have been developed by technical innovations. There is a recent trend of multi-mode, in other words multi-algorithm, wherein new CODECs are introduced in systems to achieve two-algorithm switching (two speech CODECs can be switched) or three-algorithm switching (three speech CODECs can be switched).

On the other hand, like EVRC (Enhanced Variable Rate Codec) known as the TIA (Telecommunications Industry Association) standard IS-127 in the U.S.A. or AMR (Adaptive Multi Rate), multi-rate systems have been proposed wherein one CODEC is used while plural different coding rates are supported. Moreover, a hands-free function that enables a user to make calls without having to lift his/her handset has been provided for the user's convenience.

However, in the conventional multi-mode or multi-rate communications apparatus, the noise suppressor may not fully function due to mismatching between the speech CODEC and noise suppressor in a certain selected mode or rate. As a result, high-quality transmitted speech or received speech cannot be obtained.

Furthermore, in the conventional communications apparatus with the hands-free function, in accordance with switching between the hands-free algorithm and non-hands-free algorithm, a speech input path to the noise suppressor may vary via a microphone, an analog amplifier, etc. or speech input characteristics may vary. Besides, if the environment of use changes, for example, when a new device such as an echo canceler is provided in the signal path for echo control, the noise suppressor cannot fully function and high-quality transmitted speech or received speech cannot be obtained.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is to provide a signal processing apparatus and a mobile radio communication terminal wherein a noise suppressor can fully function and high-quality speech can be transmitted and received even if the settings for use are varied due to switching of algorithm and rates or switching between a hands-free operation and a non-hands-free operation.

In order to achieve the object, the invention of claim 1 provides a signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics, suppressing background noise contained in a speech signal; a speech encoder having a plurality of different coding algorithm, encoding the suppressed speech signal by using one of the different coding algorithm; and wherein the noise suppressor selects one noise suppression characteristic in accordance with the used coding algorithm at the speech encoder.

In the signal processing apparatus with this structure, in a case where plural different coding algorithm are selectively performed, a noise component contained in a speech signal is suppressed in a front stage in association with a coding algorithm performed in a rear stage.

According to the signal processing apparatus with this structure, since the noise component is suppressed in association with the coding algorithm, the noise component is fully suppressed even if the content of the coding algorithm is varied, and high-quality speech can be transmitted.

In order to achieve the object, the invention of claim 2 provides a signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics, suppressing background noise contained in a speech signal; a speech encoder having a plurality of different coding rates, encoding the suppressed speech signal by using one of the different coding rates; and wherein the noise suppressor selects one noise suppression characteristic in accordance with the used coding rate at the speech encoder.

In the signal processing apparatus with this structure, in a case where plural different coding rates are selectively performed, a noise component contained in a speech signal is suppressed in a front stage in association with a coding rate performed in a rear stage.

According to the signal processing apparatus with this structure, since the noise component is suppressed in association with the codings rate, the noise components is fully suppressed even if the coding rate is varied, and high-quality speech can be transmitted.

In addition, in order to achieve the object, the invention of claim 10 provides a signal processing apparatus comprising: a speech decoder having a plurality of different decoding algorithm, decoding the encoded speech signal by using one of the different decoding algorithm; a noise suppressor having a plurality of different noise suppression characteristics, suppressing noise component contained in the decoded speech signal; and wherein the noise suppressor selects one noise suppression characteristics in accordance with the used decoding algorithm at the speech encoder.

In the signal processing apparatus with this structure, plural different decoding algorithm are selectively performed. When a noise component contained in the speech signal is suppressed in a rear stage, noise component suppression is performed in accordance with the performed decoding algorithm.

According to the signal processing apparatus with this structure, since the noise component is suppressed in association with the decoding algorithm, the noise component is fully suppressed even if the content of the decoding algorithm is varied, and high-quality speech can be received.

In order to achieve the object, the invention of claim 19 provides a signal processing apparatus for use in a device in which a hands-free function is selectively usable, the apparatus comprising: a noise suppressor having at least two different noise suppression characteristics, suppressing background noise contained in a speech signal; and the noise suppressor having a switch which selects a suitable suppression characteristic from the different noise suppression characteristics in accordance with the use of the hands-free function.

In the signal processing apparatus with this structure, the noise component in the input speech signal is suppressed in a manner varying depending on whether or not the speech signal has been input with use of the hands-free function.

According to the signal processing apparatus with this structure, even if the signal input path is varied depending on whether or not the speech signal has been input with use of the hands-free function, the noise component is fully suppressed and high-quality speech can be received.

In order to achieve the object, the invention of claim 22 provides a mobile radio communication terminal having a signal processing apparatus, the signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics, suppressing background noise contained in a speech signal; a speech encoder having a plurality of different coding algorithm, encoding the suppressed speech signal by using one of the different coding algorithm; and wherein the noise suppressor selects one noise suppression characteristics in accordance with the used coding algorithm at the speech encoder.

In the mobile radio communication terminal with this structure, in a case where plural different coding algorithm are selectively performed, a noise component contained in a speech signal is suppressed in a front stage in association with a coding algorithm performed in a rear stage.

According to the mobile radio communication terminal with this structure, since the noise component is suppressed in association with the coding algorithm, the noise component is fully suppressed even if the content of the coding algorithm is varied, and high-quality speech can be transmitted.

In order to achieve the object, the invention of claim 23 provides a mobile radio communication terminal having a signal processing apparatus, the signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics, suppressing background noise contained in a speech signal; a speech encoder having a plurality of different coding rates, encoding the suppressed speech signal by using one of the different coding rates; and wherein the noise suppressor selects one noise suppression characteristics in accordance with the used coding rate at the speech encoder.

In the mobile radio communication terminal with this structure, plural different decoding rates are selectively performed. When a noise component contained in the speech signal is suppressed in a rear stage, noise component suppression is performed in accordance with the used coding rate at the speech encoder.

According to the mobile radio communication terminal with this structure, since the noise component is suppressed in association with the coding rate, the noise component is fully suppressed even if the coding rate is varied, and high-quality speech can be received.

In order to achieve the object, the invention of claim 24 provides a signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics, suppressing background noise contained in a speech signal, where the number of the noise suppression characteristics is Q (Q: a positive integer); a speech encoder having a plurality of different coding algorithm, encoding the suppressed speech signal by using one of the different coding algorithm, where the number of the coding algorithm is P (P: a positive integer); and wherein the noise suppressor selects one noise suppression characteristic in accordance with the used coding algorithm at the speech encoder, the following relationship is established: P.gtoreq.Q>1.

In the signal processing apparatus with this structure, in a case where coding processes of plural different coding algorithm are selectively performed, when a noise component contained in a speech signal is to be suppressed in a front stage, a noise suppressor for suppressing the noise component in association with the coding algorithm performed in a rear stage is selected from plural noise suppressors. The relationship between the number P of the coding algorithm and the number Q of the noise suppressors is set to be: P.gtoreq.Q>1.

According to the signal processing apparatus with this structure, even where the relationship between the number P of the coding algorithm and the number Q of the noise suppressors is set to be P.gtoreq.Q>1, the noise component can be suppressed in association with the coding algorithm. Therefore, even if the content of the coding algorithm is varied, the noise component is fully suppressed and high-quality speech can be transmitted.

In order to achieve the object, the invention of claim 25 provides a signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics, suppressing background noise contained in a speech signal, where the number of the noise suppression characteristics is Q (Q: a positive integer); a speech encoder having a plurality of different coding rates, encoding the suppressed speech signal by using one of the different coding rates, where the number of the coding rates is R (R: a positive integer); and wherein the noise suppressor selects one noise suppression characteristic in accordance with the used coding rate at the speech encoder, the following relationship is established: R.gtoreq.Q>1.

In the signal processing apparatus with this structure, in a case where coding algorithm of plural different coding rates are selectively performed, when a noise component contained in a speech signal is to be suppressed in a front stage, a noise suppressor for suppressing the noise component in association with the coding algorithm performed in a rear stage is selected from plural noise suppressors. The relationship between the number R of the coding rates and the number Q of the noise suppressors is set to be: R.gtoreq.Q>1.

According to the signal processing apparatus with this structure, even where the relationship between the number R of the coding rates and the number Q of the noise suppressors is set to be R.gtoreq.Q>1, the noise component can be suppressed in association with the coding algorithm. Therefore, even if coding rate is varied, the noise component is fully suppressed and high-quality speech can be transmitted.

In order to achieve the object, the invention of claim 26 provides a signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics, suppressing background noise contained in a speech signal, the noise suppression characteristics is varied in accordance with a parameter set by a parameter setting means; a speech encoder having a plurality of different coding algorithm, encoding the suppressed speech signal by using one of the different coding algorithm, where the number of the coding algorithm is P (P: a positive integer); and wherein the parameter setting means set a suitable parameter so as to select an optimal noise suppression characteristic in accordance with the used coding algorithm at the speech encoder, where the number of the parameter is S (S: a positive integer), the following relationship is established: R.gtoreq.S>1.

In the signal processing apparatus with this structure, in a case where coding processes of plural different coding algorithm are selectively performed, when a noise component contained in a speech signal is to be suppressed in a front stage, parameters are selected from plural parameters sets for a noise suppressor so that the noise suppressor may suppress the noise component with characteristics suitable for the coding algorithm performed in a rear stage. The relationship between the number P of the coding algorithm and the number S of parameter sets is set to be: P.gtoreq.S>1.

According to the signal processing apparatus with this structure, even where the relationship between the number P of the coding algorithm and the number S of the parameter sets is set to be P.gtoreq.S>1, the noise component can be suppressed in association with the coding algorithm. Therefore, even if the content of the coding algorithm is varied, the noise component is fully suppressed and high-quality speech can be transmitted.

In order to achieve the object, the invention of claim 27 provides a signal processing apparatus comprising: a noise suppressor having a plurality of different noise suppression characteristics, suppressing background noise contained in a speech signal, the noise suppression characteristics is varied in accordance with a parameter set by a parameter setting means; a speech encoder having a plurality of different coding rates, encoding the suppressed speech signal by using one of the different coding rates, where the number of the coding rates is R (R: a positive integer); and wherein the parameter setting means set a suitable parameter so as to select an optimal noise suppression characteristic in accordance with the used coding rate at the speech encoder, where the number of the parameter is S (S: a positive integer), the following relationship is established: R.gtoreq.S>1.

In the signal processing apparatus with this structure, in a case where coding algorithm of plural different coding rates are selectively performed, when a noise component contained in a speech signal is to be suppressed in a front stage, parameters are selected from plural parameter sets for a noise suppressor so that the noise suppressor may suppress the noise component with characteristics suitable for the coding algorithm performed in a rear stage. The relationship between the number R of the coding rates and the number S of parameter sets is set to be: R.gtoreq.S>1.

According to the signal processing apparatus with this structure, even where the relationship between the number R of the coding rates and the number S of the parameter sets is set to be R.gtoreq.S>1, the noise component can be suppressed in association with the coding algorithm. Therefore, even if coding rate is varied, the noise component is fully suppressed and high-quality speech can be transmitted.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

FIG. 1 is a section block diagram showing the structure of a signal processing apparatus according to a first embodiment of the present invention;

FIG. 2 is a flow chart illustrating the operation of the signal processing apparatus according to the first embodiment shown in FIG. 1;

FIG. 3 is a section block diagram showing the structure of a signal processing apparatus according to a second embodiment of the present invention;

FIG. 4 is a flow chart illustrating the operation of the signal processing apparatus according to the second embodiment shown in FIG. 3;

FIG. 5 is a section block diagram showing the structure of a signal processing apparatus according to a third embodiment of the present invention;

FIG. 6 is a flow chart illustrating the operation of the signal processing apparatus according to the third embodiment shown in FIG. 5;

FIG. 7 is a section block diagram showing the structure of a signal processing apparatus according to a fourth embodiment of the present invention;

FIG. 8 is a flow chart illustrating the operation of the signal processing apparatus according to the fourth embodiment shown in FIG. 7;

FIG. 9 shows a schematic structure of an input speech coding section, to which the signal processing apparatus of the present invention is applied;

FIG. 10 is a section block diagram showing the structure of a modification of the third embodiment;

FIG. 11 is a graph showing a relationship between a coding process and a noise suppression process in a case where the number of kinds of coding processes is not equal to the number of kinds of noise suppression processes;

FIG. 12 shows a schematic structure of an output speech decoding section, to which the signal processing apparatus of the present invention is applied;

FIG. 13 shows an example of the structure wherein the invention is applied to the decoding systems;

FIG. 14 is a flow chart illustrating the operation of the apparatus shown in FIG. 13;

FIG. 15 is a section block diagram showing the structure of a modification of the speech coder in the signal processing apparatuses shown in FIGS. 1 7;

FIG. 16 is a section block diagram showing the structure of a modification of the noise suppressor in the signal processing apparatuses shown in FIGS. 1 7;

FIG. 17 shows an example of parameters set in the noise suppressor shown in FIG. 16;

FIG. 18 shows another example of parameters set in the noise suppressor shown in FIG. 16;

FIG. 19 shows still another example of parameters set in the noise suppressor shown in FIG. 16;

FIG. 20 is a section block diagram showing the structure of a modification of the noise suppressor in the signal processing apparatuses shown in FIGS. 1 7;

FIG. 21 is a section block diagram showing the structure of a signal processing apparatus according to a fifth embodiment of the present invention;

FIG. 22 is a flow chart illustrating the operation of the signal processing apparatus according to the fifth embodiment shown in FIG. 21;

FIG. 23 is a section block diagram showing the structure of a signal processing apparatus according to a sixth embodiment of the present invention; and

FIG. 24 is a flow chart illustrating the operation of the signal processing apparatus according to the sixth embodiment shown in FIG. 23.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 shows the structure of a signal processing apparatus according to a first embodiment of the present invention.

Reference numeral 101 denotes a microphone for capturing a user's speech, converting it to an electric analog speech signal, and taking in the analog speech signal; 102 denotes an A/D converter for converting the analog speech signal taken in by the microphone 101 to digital speech data; 110 denotes a noise suppressor for suppressing background noise contained in the speech data by digital signal processing; 103 denotes speech data in which background noise has been suppressed by the noise suppressor 110; 120 denotes a speech coder for compressing and coding the digital speech data 103; and 104 denotes coded data compressed by the speech coder 120.

The speech coder 120 includes, as three sections for coding speech data by different algorithm, an Algorithm-A coding section 121, an Algorithm-B coding section 122 and an Algorithm-C coding section 123. In addition, the speech coder 120 includes a coding algorithm switching control section 124.

For example, the Algorithm-A coding section 121 performs a coding process in which the coding rate is low but the quality of coded sound relative to background noise is not good. The Algorithm-C coding section 123 performs a coding process in which the coding rate is high and the quality of coded sound relative to background noise is relatively good. The Algorithm-B coding section 122 performs a coding process capable of obtaining an intermediate speech quality between the Algorithm-A coding section 121 and the Algorithm-C coding section 123.

In response to an external coding algorithm select command 105, the coding algorithm switching control section 124 effects switching among the Algorithm-A coding section 121, Algorithm-B coding section 122 and Algorithm-C coding section 123 so that one of them may function. In addition, the coding algorithm switching control section 124 delivers information representative of the coding algorithm chosen by the switching to the noise suppressor 110 as coding algorithm select information 106.

The noise suppressor 110 includes, as three sections for suppressing background noise by different algorithm, an Algorithm-X noise suppress section 111, an Algorithm-Y noise suppress section 112 and an Algorithm-Z noise suppress section 113. Each noise suppress section has each different noise suppression characteristic. In addition, the noise suppressor 110 includes a suppress algorithm switching control section 114.

In response to the coding algorithm select information 106, the suppress algorithm switching control section 114 effects switching among the Algorithm-X noise suppress section 111, Algorithm-Y noise suppress section 112 and Algorithm-Z noise suppress section 113 so that an optimal one of them may function.

In the switching control by the suppress algorithm switching control section 114, the optimal noise suppress section (111, 112 or 113) is made to function in association with the coding section (121, 122 or 123) activated in the speech coder 120. Specifically, where the Algorithm-A coding section 121 functions, the Algorithm-X noise suppress section 111 is selected by the coding algorithm select information 106. Where the Algorithm-B coding section 122 functions, the Algorithm-Y noise suppress section 112 is selected by the coding algorithm select information 106. Where the Algorithm-C coding section 123 functions, the Algorithm-Z noise suppress section 113 is selected by the coding algorithm select information 106.

In order to optimize the correspondency between the coding section and the noise suppress section, the Algorithm-X noise suppress section 111, for example, adopts a spectral subtraction (SS) method in a frequency domain with a high noise suppress performance, although somewhat complex processing needs to be performed. The Algorithm-Y noise suppress section 112 adopts a similar SS method, in which, however, less complex processing needs to be performed than in the Algorithm-X noise suppress section 111. The Algorithm-Z noise suppress section 113 adopts an adaptive filtering method in a dime domain with a relatively simple scheme.

The operation of the signal processing apparatus according to the first embodiment will now be described. FIG. 2 is a flow chart illustrating this operation.

In a command input standby state in step 2a, if the coding algorithm select command 105 to the effect that "Use the Algorithm-A as the coding algorithm" has been input to the coding algorithm switching control section 124, control advances to step 2b to determine the designated coding algorithm. Since the designated coding algorithm is the Algorithm-A in this case, control goes to step 2c.

In step 2c, the coding algorithm switching control section 124 controls switching so that the digital data 103 may be input to the Algorithm-A coding section 121. Accordingly, the Algorithm-A coding section 121 begins coding the input digital data 103.

In step 2c, in parallel with the switching control, the coding algorithm switching control section 124 outputs, as the coding algorithm select information 106, the information to the effect that the Algorithm-A coding section 121 is to be used for coding the digital data 103 to the suppress algorithm switching control section 114. Control then goes to step 2d.

In step 2d, the suppress algorithm switching control section 114 controls switching so that the output from the A/D converter 102 may enter the Algorithm-X noise suppress section 111, thereby effecting noise suppression by the Algorithm-X noise suppress section 111, which is optimized for the coding by the Algorithm-A coding section 121. Control then goes to step 2i.

With this switching control operation, the output from the A/D converter 102 is subjected to noise suppression in the Algorithm-X noise suppress section 111. The output from the Algorithm-X noise suppress section 111 is input to the Algorithm-A coding section 121 as digital data 103. The digital data 103 is coded in the Algorithm-A coding section 121 and the resultant data is output as coded data 104.

In step 2i, if the coding algorithm select command 105 to the effect that "Use the Algorithm-B as the coding algorithm" has been input to the coding algorithm switching control section 124, control advances to step 2b to determine the designated coding algorithm. Since the designated coding algorithm is the Algorithm-B in this case, control goes to step 2e.

In step 2e, the coding algorithm switching control section 124 controls switching at a proper timing so that the digital data 103 may be input to the Algorithm-B coding section 122. Accordingly, the Algorithm-A coding section. 121 stops functioning, and instead the Algorithm-B coding section 122 begins coding the input digital data 103.

In step 2e, in parallel with the switching control, the coding algorithm switching control section 124 outputs, as the coding algorithm select information 106, the information to the effect that the Algorithm-B coding section 122 is to be used for coding the digital data 103 to the suppress algorithm switching control section 114. Control then goes to step 2f.

In step 2f, the suppress algorithm switching control section 114 controls switching so that the output from the A/D converter 102 may enter the Algorithm-Y noise suppress section 112, thereby effecting noise suppression by the Algorithm-Y noise suppress section 112, which is optimized for the coding by the Algorithm-B coding section 122. Control then goes to step 2i.

With this switching control operation, the output from the A/D converter 102 is subjected to noise suppression in the Algorithm-Y noise suppress section 112. The output from the Algorithm-Y noise suppress section 112 is input to the Algorithm-B coding section 122 as digital data 103. The digital data 103 is coded in the Algorithm-B coding section 122 and the resultant data is output as coded data 104.

In step 2i, if the coding algorithm select command 105 to the effect that "Use the Algorithm-C as the coding algorithm" has been input to the coding algorithm switching control section 124 while the digital data 103 is being coded in the Algorithm-A coding section 121 or Algorithm-B coding section 122 as described above, control advances to step 2b to determine the designated coding algorithm. Since the designated coding algorithm is the Algorithm-C in this case, control goes to step 2g.

In step 2g, the coding algorithm switching control section 124 controls switching at a proper timing so that the digital data 103 may be input to the Algorithm-C coding section 123. Accordingly, the Algorithm-A coding section 121 or Algorithm-B coding section 122 stops functioning, and instead the Algorithm-C coding section 123 begins coding the input digital data 103.

In step 2g, in parallel with the switching control, the coding algorithm switching control section 124 outputs, as the coding algorithm select information 106, the information to the effect that the Algorithm-C coding section 123 is to be used for coding the digital data 103 to the suppress algorithm switching control section 114. Control then goes to step 2h.

In step 2h, the suppress algorithm switching control section 114 controls switching so that the output from the A/D converter 102 may enter the Algorithm-Z noise suppress section 113, thereby effecting noise suppression by the Algorithm-Z noise suppress section 113, which is optimized for the coding by the Algorithm-C coding section 123. Control then goes to step 2i.

With this switching control operation, the output from the A/D converter 102 is subjected to noise suppression in the Algorithm-Z noise suppress section 113. The output from the Algorithm-Z noise suppress section 113 is input to the Algorithm-C coding section 123 as digital data 103. The digital data 103 is coded in the Algorithm-C coding section 123 and the resultant data is output as compressed coded data 104.

In step 2i, if no command is input, control goes to step 2j. In step 2j, it is determined whether a communication end request is input. If the communication end request has been input, the present process is finished. If the communication end request is not input, command input is monitored once again in step 2i.

As has been described above, in the signal processing apparatus having the above structure, when the compressed coded data 104 is to be acquired, the optimal noise suppress section (111, 112 or 113) is activated in accordance with the coding section (121, 122 or 123) functioning in the speech coder 120.

According to the signal processing apparatus with the above structure, noise suppression is effected by the optimal noise suppress section for the coding by the speech coder 120. Thus, the noise suppress section functions with high performance, and high-quality speech can be transmitted.

The present invention is not limited to the above-described embodiment. For example, in the first embodiment, the suppress algorithm switching control section 114 functions to activate the optimal noise suppress section in accordance with the coding section functioning in the speech coder 120, on the basis of the coding algorithm select information 106 from the coding algorithm switching control section 124.

Instead, the suppress algorithm switching control section 114 may function to activate the optimal noise suppress section in accordance with the coding section functioning in the speech coder 120, on the basis of the coding algorithm select command 105. With this modification, the same advantage can also be obtained.

In this case, the suppress algorithm switching control section 114 controls switching to activate the optimal noise suppress section at a proper timing in consideration of the switching timing of the coding section in the speech coder 120.

A signal processing apparatus according to a second embodiment of the present invention will now be described. FIG. 3 shows the structure of this signal processing apparatus.

Reference numeral 201 denotes a microphone for capturing a user's call speech, converting it to an electric analog speech signal, and taking in the analog speech signal; 202 an A/D converter for converting the analog speech signal taken in by the microphone 201 to digital speech data; 210 a noise suppressor for suppressing background noise contained in the speech data by digital signal processing; 203 speech data in which background noise has been suppressed by the noise suppressor 210; 220 a speech coder for compressing and coding the digital speech data 203; and 204 coded data compressed by the speech coder 220.

The speech coder 220 includes, as three sections for coding speech data by different algorithm, an Algorithm-A coding section 221, an Algorithm-B coding section 222 and an Algorithm-C coding section 223. In addition, the speech coder 220 includes a coding algorithm switching control section 224.

For example, the Algorithm-A coding section 221 performs a coding process in which the coding rate is low but the quality of coded sound relative to background noise is not good. The Algorithm-C coding section 223 performs a coding process in which the coding rate is high and the quality of coded sound relative to background noise is relatively good. The Algorithm-B coding section 222 performs a coding process capable of obtaining an intermediate speech quality between the Algorithm-A coding section 221 and the Algorithm-C coding section 223.

In response to an external coding algorithm select command 205, the coding algorithm switching control section 224 effects switching among the Algorithm-A coding section 221, Algorithm-B coding section 222 and Algorithm-C coding section 223 so that one of them may function. In addition, the coding algorithm switching control section 224 delivers information representative of the coding algorithm chosen by the switching to the noise suppressor 210 as coding algorithm select information 206.

The noise suppressor 210 comprises a noise suppress section 215, a parameter table 216 and a parameter switching control section 217.

The noise suppress section 215 suppresses background noise contained in speech data output from the A/D converter 202. The suppression characteristics for background noise suppression are controlled by parameters input from the parameter table 216.

The parameter table 216 stores parameters for setting the characteristics for background noise suppression to be effected by the noise suppress section 215. Specifically, the parameter table 216 stores three parameter sets for providing optimal noise suppression characteristics for the respective coding algorithm of the Algorithm-A coding section 221, Algorithm-B coding section 222 and Algorithm-C coding section 223. An optimal one of the parameter sets is input to the noise suppress section 215 by the control of the parameter switching control section 217.

In the present embodiment, it is assumed that each parameter set comprises five parameters, and parameter sets (three in this embodiment) are prepared for the respective coding algorithm.

The parameter switching control section 217 controls the parameter table 216. Thus, based on the coding algorithm select information 206, one of the parameter sets, which is optimal for the coding section (221, 222 or 223) functioning in the speech coder 220, can be selectively set in the noise suppress section 215.

In order to optimize the correspondency between the coding section and the parameter setting (noise suppress characteristic setting) in the noise suppress section, the parameter set associated with the Algorithm-A coding section 221, for example, realizes such characteristics as to provide a relatively large noise suppression amount and to reduce noise as much as possible even if some distortion occurs in the speech component. The parameter set associated with the Algorithm-C coding section 223 realizes such characteristics as to provide a relatively small noise suppression amount and to pass noise which can be naturally heard.

The parameter set associated with the Algorithm-B coding section 222 provides intermediate characteristics between those for the Algorithm-A coding section 221 and those for the Algorithm-C coding section 223.

The operation of the signal processing apparatus according to the second embodiment will now be described. FIG. 4 is a flow chart illustrating this operation.

In a command input standby state in step 4a, if the coding algorithm select command 205 to the effect that "Use the Algorithm-A as the coding algorithm" has been input to the coding algorithm switching control section 224, control advances to step 4b to determine the designated coding algorithm. Since the designated coding algorithm is the Algorithm-A in this case, control goes to step 4c.

In step 4c, the coding algorithm switching control section 224 controls switching so that the digital data 203 may be input to the Algorithm-A coding section 221. Accordingly, the Algorithm-A coding section 221 begins coding the input digital data 203.

In step 4c, in parallel with the switching control, the coding algorithm switching control section 224 outputs, as the coding algorithm select information 206, the information to the effect that the Algorithm-A coding section 221 is to be used for coding the digital data 203 to the parameter switching control section 217. Control then goes to step 4d.

In step 4d, the para