CA2060310C - Digital speech coder with vector excitation source having improved speech quality - Google Patents
Digital speech coder with vector excitation source having improved speech quality Download PDFInfo
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- CA2060310C CA2060310C CA002060310A CA2060310A CA2060310C CA 2060310 C CA2060310 C CA 2060310C CA 002060310 A CA002060310 A CA 002060310A CA 2060310 A CA2060310 A CA 2060310A CA 2060310 C CA2060310 C CA 2060310C
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- Prior art keywords
- excitation
- excitation signal
- signal
- candidate
- pitch
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Classifications
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L13/00—Speech synthesis; Text to speech systems
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
- G10L19/08—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
- G10L19/12—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L2019/0001—Codebooks
- G10L2019/0004—Design or structure of the codebook
- G10L2019/0005—Multi-stage vector quantisation
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L2019/0001—Codebooks
- G10L2019/0011—Long term prediction filters, i.e. pitch estimation
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L2019/0001—Codebooks
- G10L2019/0013—Codebook search algorithms
Abstract
In a vector excitation source digital speech coder utilizing vector excitation, candidate excitation sources (111, 121) are con-sidered independent of certain pitch parameters. Once a particular excitation source has been selected, the excluded pitch par-ameter may then be optimized, resulting in an overall improvement in speech quality.
Description
DIGITAL SPEECH CODER WITH VECTOR EXCITATION
SOURCE HAVING IMPROVED SPEECH QUALITY
Technical Field This invention relates generally to speech coders, and more particularly to digital speech coders that use vector excitation sources.
Background of the Invention Speech coders are known in the art. Some speech coders convert analog voice samples into digitized representations, and subsequently represent the spectral speech information through use of linear predictive coding. Other speech coders improve upon ordinary linear predictive coding techniques by providing an excitation signal that is related to the original voice signal. I have described, in previously issued U.S. Patent No. 4,817,157, a digital speech coder having an improved vector excitation source wherein a codebook of excitation vectors is accessed to select an excitation signal that best fits the available information, and hence provides a recovered speech signal that closely represents the original.
In general, the resultant decoded speech signal will more closely represent the original unencoded speech signal if there is a significant number of candidate excitation vectors available for consideration as the excitation source. Increasing performance in this way, however, generally results in enlargement of the codebpok size, and this will usually increase processing complexity and data rates.
A need therefore exists for a digital speech coder that uses a vector excitation signal, wherein for a given size codebook, the quality of the decoded speech signal is substantially maximized with minimal increase in complexity and substantially no increase in data rate.
Summary of the Invention These needs and others are substantially met through provision of the digital speech coder with vector excitation source having improved speech quality disclosed herein. Pursuant to this invention, when encoding a signal sample, such as a speech sample, the coder first determines a pitch period parameter for the speech sample. Relying in part upon this pitch period parameter, a particular coded excitation signal can be determined independent of the pitch filter coefficient, following which the pitch filter coefficient parameter can be optimized for that particular speech sample.
This methodology allows candidate excitation signals to be considered without requiring a commensurate increase in processing complexity or data rates.
In one embodiment, the coded excitation signal is determined substantially independent from any pitch information. In particular, candidate excitation signals as provided by a codebook are processed to substantially remove components that are representable, at least in part, by a reference component that is related, at least in part, to the intermediate pitch vector. More particularly, the vector component related to the intermediate pitch vector is removed from the candidate excitation signal (a process known as orthogonalizing).
The orthogonalized candidate excitation signals are then compared with the unencoded speech sample to identify the candidate excitation signal that best represents this particular speech sample. The pitch information, including a pitch filter coefficient parameter, can be optimized later to best suit the selected excitation signal to thereby yield an overall optimized coded representation of the speech signal.
In another embodiment, a second codebook of candidate excitation signals, wherein two excitation signals are used to represent the speech sample, is provided. The first excitation signal can be selected as described above, and the second excitation signal can be selected in a similar manner, wherein candidate second excitation signals are first orthogonalized with respect to both the intermediate pitch vector and the previously selected first excitation signal.
Brief Description of the Drawin, Fig. 1 comprises a block diagrammatic depiction of the invention; and Fig. 2 cow rises a simple vector diagram representing one aspect of the invention.
SOURCE HAVING IMPROVED SPEECH QUALITY
Technical Field This invention relates generally to speech coders, and more particularly to digital speech coders that use vector excitation sources.
Background of the Invention Speech coders are known in the art. Some speech coders convert analog voice samples into digitized representations, and subsequently represent the spectral speech information through use of linear predictive coding. Other speech coders improve upon ordinary linear predictive coding techniques by providing an excitation signal that is related to the original voice signal. I have described, in previously issued U.S. Patent No. 4,817,157, a digital speech coder having an improved vector excitation source wherein a codebook of excitation vectors is accessed to select an excitation signal that best fits the available information, and hence provides a recovered speech signal that closely represents the original.
In general, the resultant decoded speech signal will more closely represent the original unencoded speech signal if there is a significant number of candidate excitation vectors available for consideration as the excitation source. Increasing performance in this way, however, generally results in enlargement of the codebpok size, and this will usually increase processing complexity and data rates.
A need therefore exists for a digital speech coder that uses a vector excitation signal, wherein for a given size codebook, the quality of the decoded speech signal is substantially maximized with minimal increase in complexity and substantially no increase in data rate.
Summary of the Invention These needs and others are substantially met through provision of the digital speech coder with vector excitation source having improved speech quality disclosed herein. Pursuant to this invention, when encoding a signal sample, such as a speech sample, the coder first determines a pitch period parameter for the speech sample. Relying in part upon this pitch period parameter, a particular coded excitation signal can be determined independent of the pitch filter coefficient, following which the pitch filter coefficient parameter can be optimized for that particular speech sample.
This methodology allows candidate excitation signals to be considered without requiring a commensurate increase in processing complexity or data rates.
In one embodiment, the coded excitation signal is determined substantially independent from any pitch information. In particular, candidate excitation signals as provided by a codebook are processed to substantially remove components that are representable, at least in part, by a reference component that is related, at least in part, to the intermediate pitch vector. More particularly, the vector component related to the intermediate pitch vector is removed from the candidate excitation signal (a process known as orthogonalizing).
The orthogonalized candidate excitation signals are then compared with the unencoded speech sample to identify the candidate excitation signal that best represents this particular speech sample. The pitch information, including a pitch filter coefficient parameter, can be optimized later to best suit the selected excitation signal to thereby yield an overall optimized coded representation of the speech signal.
In another embodiment, a second codebook of candidate excitation signals, wherein two excitation signals are used to represent the speech sample, is provided. The first excitation signal can be selected as described above, and the second excitation signal can be selected in a similar manner, wherein candidate second excitation signals are first orthogonalized with respect to both the intermediate pitch vector and the previously selected first excitation signal.
Brief Description of the Drawin, Fig. 1 comprises a block diagrammatic depiction of the invention; and Fig. 2 cow rises a simple vector diagram representing one aspect of the invention.
6~~~,0 Best Mode For Carr~g Out The Invention:
This invention can be embodied in a speech coder 5 that makes use of an appropriate digital signal processor such as a Motorola DSP 56000 family device. The computational functions of such a DSP embodiment are represented in Fig. 1 as a block diagram equivalent circuit.
10 A pitch period parameter (101 ) (determined in accordance with prior art technique) is provided to a pitch filter state (102) that comprises part of a pitch filter. The resultant signal (103) comprises an intermediate pitch vector that is provided to both a first 15 multiplier (104) and two orthogonalizing processes (106 and 107) as described below in more detail. This first multiplier (104) functions to multiply the resultant signal by a pitch filter coefficient (108) to yield a pitch filter output (109). Selection of the pitch filter 20 coefficient (108) will be described below in more detail.
A first codebook (111 ) includes a set of basis vectors that can be linearly combined to form a plurality of resultant excitation signals. Depending upon the size of the memory utilized, and other factors appropriate to the application, the number of possible resultant excitation signals can be, for example, between 64 and 2,048, with more of course being possible when appropriate to a particular application. The problem, when encoding a particular speech sample, is to select whichever of these excitation sources best represents the corresponding component of the original speech information.
Pursuant to this invention, once a particular resultant signal (103) has been determined, the excitation signals formulated by the first codebook (111 ) will be presented in seriatim fashion as candidate 5 excitation sources. Each candidate excitation source will first be orthogonalized (106) with respect to the resultant signal. For example, referring momentarily to Fig. 2, if vector A were considered to represent the resultant signal and vector B were to represent a particular candidate excitation source, orthogonalization of the candidate excitation source signal would result in the vector denoted by reference character B'. (It should be understood that in practice, the vector dimension space is a function of the number of samples comprising the vectors, which may be upwards of 40 samples or more. It should also be noted that the candidate excitation vectors may be readily orthogonalized by orthogonalizing the basis vectors, wherein linear combinations of the orthogonadized basis vectors with one another will result in orthogonalized excitation vectors.) Once orthogonalized, the resulting candidate excitation source can be compared (112) with the unencoded signal (113) (or an appropriate representative signal based thereon) to determine the relative similarity or disparity between the two. The process is then repeated for each of the excitation sources of the first codebook (111 ). A determination can then be made as to which candidate excitation source most closely aligns with the unencoded signal (113).
In this particular embodiment, a gain factor (114) can also be used to modify each candidate excitation 2~ source signal, as well understood in the art. In addition, if desired, the excitation source selection and gain compensation can both be accomplished in a substantially simultaneous manner, as also well understood in the art.
Once an appropriate excitation source from the first codebook (111 ) has been selected through this process, the orthogonalizing process (106) can thereafter be dispensed with and the exact excitation source signal selected (116) through an appropriate control mechanism (117). Thereafter, presuming a single codebook coder, the pitch information can be gated (117) and summed (118) together with the selected excitation source with the pitch filter coefficient (108) and excitation gain (114) optimized such that the combined excitation most closely aligns with the encoded signal (113). Once optimized, the pitch period parameter, pitch filter coefficient, and particular excitation source and gain are known, and appropriate representations thereof may be utilized thereafter as representative of the original speech sample.
If desired, and as depicted in Fig. 1, an additional codebook (121 ) can be utilized, which second codebook (121 ) again includes a plurality of basis vector derived candidate excitation sources. The use of such multiple codebooks is understood in the art. Pursuant to this invention, however, once the first excitation source from the first codebook (111 ) has been selected as described above, the candidate excitation sources from the second codebook (121 ) are orthogonalized (107) with respect to both the resultant signal (103) and the selected excitation source signal from the first ccdebook (111 ). The selection process can then continue as described above, with the orthogonalized candidate excitation source signals from the second codebook (121 ) being compared against a representative unencoded signal (113) to identify the closest fit. Once this excitation source has been selected, the pitch filter coefficient (108) and excitation gains (114 and 120) can then be optimized as described above.
What is claimed is:
This invention can be embodied in a speech coder 5 that makes use of an appropriate digital signal processor such as a Motorola DSP 56000 family device. The computational functions of such a DSP embodiment are represented in Fig. 1 as a block diagram equivalent circuit.
10 A pitch period parameter (101 ) (determined in accordance with prior art technique) is provided to a pitch filter state (102) that comprises part of a pitch filter. The resultant signal (103) comprises an intermediate pitch vector that is provided to both a first 15 multiplier (104) and two orthogonalizing processes (106 and 107) as described below in more detail. This first multiplier (104) functions to multiply the resultant signal by a pitch filter coefficient (108) to yield a pitch filter output (109). Selection of the pitch filter 20 coefficient (108) will be described below in more detail.
A first codebook (111 ) includes a set of basis vectors that can be linearly combined to form a plurality of resultant excitation signals. Depending upon the size of the memory utilized, and other factors appropriate to the application, the number of possible resultant excitation signals can be, for example, between 64 and 2,048, with more of course being possible when appropriate to a particular application. The problem, when encoding a particular speech sample, is to select whichever of these excitation sources best represents the corresponding component of the original speech information.
Pursuant to this invention, once a particular resultant signal (103) has been determined, the excitation signals formulated by the first codebook (111 ) will be presented in seriatim fashion as candidate 5 excitation sources. Each candidate excitation source will first be orthogonalized (106) with respect to the resultant signal. For example, referring momentarily to Fig. 2, if vector A were considered to represent the resultant signal and vector B were to represent a particular candidate excitation source, orthogonalization of the candidate excitation source signal would result in the vector denoted by reference character B'. (It should be understood that in practice, the vector dimension space is a function of the number of samples comprising the vectors, which may be upwards of 40 samples or more. It should also be noted that the candidate excitation vectors may be readily orthogonalized by orthogonalizing the basis vectors, wherein linear combinations of the orthogonadized basis vectors with one another will result in orthogonalized excitation vectors.) Once orthogonalized, the resulting candidate excitation source can be compared (112) with the unencoded signal (113) (or an appropriate representative signal based thereon) to determine the relative similarity or disparity between the two. The process is then repeated for each of the excitation sources of the first codebook (111 ). A determination can then be made as to which candidate excitation source most closely aligns with the unencoded signal (113).
In this particular embodiment, a gain factor (114) can also be used to modify each candidate excitation 2~ source signal, as well understood in the art. In addition, if desired, the excitation source selection and gain compensation can both be accomplished in a substantially simultaneous manner, as also well understood in the art.
Once an appropriate excitation source from the first codebook (111 ) has been selected through this process, the orthogonalizing process (106) can thereafter be dispensed with and the exact excitation source signal selected (116) through an appropriate control mechanism (117). Thereafter, presuming a single codebook coder, the pitch information can be gated (117) and summed (118) together with the selected excitation source with the pitch filter coefficient (108) and excitation gain (114) optimized such that the combined excitation most closely aligns with the encoded signal (113). Once optimized, the pitch period parameter, pitch filter coefficient, and particular excitation source and gain are known, and appropriate representations thereof may be utilized thereafter as representative of the original speech sample.
If desired, and as depicted in Fig. 1, an additional codebook (121 ) can be utilized, which second codebook (121 ) again includes a plurality of basis vector derived candidate excitation sources. The use of such multiple codebooks is understood in the art. Pursuant to this invention, however, once the first excitation source from the first codebook (111 ) has been selected as described above, the candidate excitation sources from the second codebook (121 ) are orthogonalized (107) with respect to both the resultant signal (103) and the selected excitation source signal from the first ccdebook (111 ). The selection process can then continue as described above, with the orthogonalized candidate excitation source signals from the second codebook (121 ) being compared against a representative unencoded signal (113) to identify the closest fit. Once this excitation source has been selected, the pitch filter coefficient (108) and excitation gains (114 and 120) can then be optimized as described above.
What is claimed is:
Claims (9)
1. A method of encoding a speech sample, comprising the steps of:
A) determining a pitch period parameter for the speech sample;
B) determining, independent of any pitch filter coefficient, a plurality of coded excitation signals for the speech sample;
C) processing each of the plurality of coded excitation signals to provide a plurality of processed candidate excitation signals, wherein each of the plurality of processed candidate excitation signals is comprised of information that is substantially independent of information that is representable by a pitch filter output that is derived, at least in part, as a function of the pitch period parameter;
D) optimizing at least a pitch filter coefficient parameter for the speech sample.
A) determining a pitch period parameter for the speech sample;
B) determining, independent of any pitch filter coefficient, a plurality of coded excitation signals for the speech sample;
C) processing each of the plurality of coded excitation signals to provide a plurality of processed candidate excitation signals, wherein each of the plurality of processed candidate excitation signals is comprised of information that is substantially independent of information that is representable by a pitch filter output that is derived, at least in part, as a function of the pitch period parameter;
D) optimizing at least a pitch filter coefficient parameter for the speech sample.
2. The method of claim 1 further characterized in that the step of determining a coded excitation signal includes processing the plurality of candidate excitation signals to orthogonalize the plurality of candidate excitation signals with respect to a pitch filter output that is derived, at least in part, as a function of the pitch period parameter.
3. The method of claim 1, further characterized in that the step of determining the coded excitation signal comprises the steps of:
B1) processing an excitation signal to substantially remove components that are representable, at least in part, by a reference that is related, at least in part, to the pitch period parameter;
and.
B2) determining an appropriate excitation signal for the speech sample.
B1) processing an excitation signal to substantially remove components that are representable, at least in part, by a reference that is related, at least in part, to the pitch period parameter;
and.
B2) determining an appropriate excitation signal for the speech sample.
4. A method of claim 3 further characterized in that the step of processing the excitation signal includes processing the excitation signal to orthogonalize the excitation signal with respect to a pitch filter output that is derived, at least in part, as a function of the pitch period parameter.
5. The method of claim 3, and further characterized by the step of:
C1) processing a candidate excitation signal to substantially remove components that are representable at least in part, by:
a reference that is related, at least in part, to the pitch period parameter; and the appropriate excitation signal determined in step B2.
C1) processing a candidate excitation signal to substantially remove components that are representable at least in part, by:
a reference that is related, at least in part, to the pitch period parameter; and the appropriate excitation signal determined in step B2.
6. The method of claim 5 further characterized in that the step of processing a candidate excitation signal includes processing the candidate excitation signal to orthogonalize the candidate excitation signal with respect to both the reference and the appropriate excitation signal determined in step B2.
7. A method of encoding a signal sample using at least two codebooks that include information regarding candidate excitation signals, comprising the steps of:
A) determining, using a first one of the codebooks, a first excitation signal for the signal sample; characterized by:
B) determining, using a second one of the codebooks, a second excitation signal for the signal sample, which second excitation signal is comprised of information that is substantially independent of information that is representable by the first excitation signal;
C) using the first and second excitation signals to represent, at least in part, the signal sample.
A) determining, using a first one of the codebooks, a first excitation signal for the signal sample; characterized by:
B) determining, using a second one of the codebooks, a second excitation signal for the signal sample, which second excitation signal is comprised of information that is substantially independent of information that is representable by the first excitation signal;
C) using the first and second excitation signals to represent, at least in part, the signal sample.
8. The method of claim 7 further characterized in that the signal sample comprises a speech sample.
9. The method of claim 7 further characterized in that the step of determining the second excitation signal includes processing a candidate excitation signal to orthogonalize the candidate excitation signal with respect to the first excitation signal.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US37054189A | 1989-06-23 | 1989-06-23 | |
| US370,541 | 1989-07-23 | ||
| PCT/US1990/002469 WO1991001545A1 (en) | 1989-06-23 | 1990-05-02 | Digital speech coder with vector excitation source having improved speech quality |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2060310A1 CA2060310A1 (en) | 1990-12-24 |
| CA2060310C true CA2060310C (en) | 2001-07-17 |
Family
ID=23460115
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002060310A Expired - Lifetime CA2060310C (en) | 1989-06-23 | 1990-05-02 | Digital speech coder with vector excitation source having improved speech quality |
Country Status (10)
| Country | Link |
|---|---|
| EP (1) | EP0484339B1 (en) |
| KR (1) | KR950003557B1 (en) |
| CN (1) | CN1023160C (en) |
| AU (1) | AU638462B2 (en) |
| BR (1) | BR9007467A (en) |
| CA (1) | CA2060310C (en) |
| DE (1) | DE69032026T2 (en) |
| IL (1) | IL94119A (en) |
| NZ (1) | NZ234180A (en) |
| WO (1) | WO1991001545A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0451200A (en) * | 1990-06-18 | 1992-02-19 | Fujitsu Ltd | Sound encoding system |
| JPH0451199A (en) * | 1990-06-18 | 1992-02-19 | Fujitsu Ltd | Sound encoding/decoding system |
| IT1241358B (en) * | 1990-12-20 | 1994-01-10 | Sip | VOICE SIGNAL CODING SYSTEM WITH NESTED SUBCODE |
| JP2776050B2 (en) * | 1991-02-26 | 1998-07-16 | 日本電気株式会社 | Audio coding method |
| DE4315315A1 (en) * | 1993-05-07 | 1994-11-10 | Ant Nachrichtentech | Method for vector quantization, especially of speech signals |
| SG43128A1 (en) * | 1993-06-10 | 1997-10-17 | Oki Electric Ind Co Ltd | Code excitation linear predictive (celp) encoder and decoder |
| JP3224955B2 (en) * | 1994-05-27 | 2001-11-05 | 株式会社東芝 | Vector quantization apparatus and vector quantization method |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1252568A (en) * | 1984-12-24 | 1989-04-11 | Kazunori Ozawa | Low bit-rate pattern encoding and decoding capable of reducing an information transmission rate |
| US4868867A (en) * | 1987-04-06 | 1989-09-19 | Voicecraft Inc. | Vector excitation speech or audio coder for transmission or storage |
| US4899385A (en) * | 1987-06-26 | 1990-02-06 | American Telephone And Telegraph Company | Code excited linear predictive vocoder |
-
1990
- 1990-04-18 IL IL9411990A patent/IL94119A/en not_active IP Right Cessation
- 1990-05-02 AU AU57359/90A patent/AU638462B2/en not_active Expired
- 1990-05-02 KR KR1019910701947A patent/KR950003557B1/en not_active IP Right Cessation
- 1990-05-02 WO PCT/US1990/002469 patent/WO1991001545A1/en active IP Right Grant
- 1990-05-02 DE DE69032026T patent/DE69032026T2/en not_active Expired - Lifetime
- 1990-05-02 BR BR909007467A patent/BR9007467A/en not_active IP Right Cessation
- 1990-05-02 EP EP90908908A patent/EP0484339B1/en not_active Expired - Lifetime
- 1990-05-02 CA CA002060310A patent/CA2060310C/en not_active Expired - Lifetime
- 1990-06-19 CN CN90103020A patent/CN1023160C/en not_active Expired - Lifetime
- 1990-06-21 NZ NZ234180A patent/NZ234180A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE69032026T2 (en) | 1998-09-17 |
| CA2060310A1 (en) | 1990-12-24 |
| CN1048278A (en) | 1991-01-02 |
| EP0484339B1 (en) | 1998-02-04 |
| DE69032026D1 (en) | 1998-03-12 |
| NZ234180A (en) | 1993-11-25 |
| KR950003557B1 (en) | 1995-04-14 |
| IL94119A0 (en) | 1991-01-31 |
| AU638462B2 (en) | 1993-07-01 |
| KR920702787A (en) | 1992-10-06 |
| EP0484339A4 (en) | 1993-05-05 |
| BR9007467A (en) | 1992-06-16 |
| CN1023160C (en) | 1993-12-15 |
| IL94119A (en) | 1996-06-18 |
| AU5735990A (en) | 1991-02-22 |
| WO1991001545A1 (en) | 1991-02-07 |
| EP0484339A1 (en) | 1992-05-13 |
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