EP0135512A4 - Improved method and means of determining coefficients for linear predictive coding. - Google Patents
Improved method and means of determining coefficients for linear predictive coding.Info
- Publication number
- EP0135512A4 EP0135512A4 EP19840900575 EP84900575A EP0135512A4 EP 0135512 A4 EP0135512 A4 EP 0135512A4 EP 19840900575 EP19840900575 EP 19840900575 EP 84900575 A EP84900575 A EP 84900575A EP 0135512 A4 EP0135512 A4 EP 0135512A4
- Authority
- EP
- European Patent Office
- Prior art keywords
- coefficients
- signal
- ram
- sequencer
- lattice
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000000034 method Methods 0.000 title claims abstract description 32
- 238000001914 filtration Methods 0.000 claims abstract description 4
- 238000012545 processing Methods 0.000 claims description 3
- 230000005236 sound signal Effects 0.000 claims description 2
- XUKUURHRXDUEBC-KAYWLYCHSA-N Atorvastatin Chemical group C=1C=CC=CC=1C1=C(C=2C=CC(F)=CC=2)N(CC[C@@H](O)C[C@@H](O)CC(O)=O)C(C(C)C)=C1C(=O)NC1=CC=CC=C1 XUKUURHRXDUEBC-KAYWLYCHSA-N 0.000 claims 1
- 239000011159 matrix material Substances 0.000 abstract description 19
- 238000004364 calculation method Methods 0.000 abstract description 10
- 238000005070 sampling Methods 0.000 abstract description 4
- 230000000694 effects Effects 0.000 abstract description 3
- 230000006870 function Effects 0.000 description 11
- 238000010586 diagram Methods 0.000 description 10
- 238000004458 analytical method Methods 0.000 description 8
- 102100021878 Neuronal pentraxin-2 Human genes 0.000 description 5
- 101710155147 Neuronal pentraxin-2 Proteins 0.000 description 5
- 210000001260 vocal cord Anatomy 0.000 description 3
- 230000001755 vocal effect Effects 0.000 description 3
- APOYTRAZFJURPB-UHFFFAOYSA-N 2-methoxy-n-(2-methoxyethyl)-n-(trifluoro-$l^{4}-sulfanyl)ethanamine Chemical compound COCCN(S(F)(F)F)CCOC APOYTRAZFJURPB-UHFFFAOYSA-N 0.000 description 2
- 238000004590 computer program Methods 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000013139 quantization Methods 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- NUHSROFQTUXZQQ-UHFFFAOYSA-N isopentenyl diphosphate Chemical compound CC(=C)CCO[P@](O)(=O)OP(O)(O)=O NUHSROFQTUXZQQ-UHFFFAOYSA-N 0.000 description 1
- PWPJGUXAGUPAHP-UHFFFAOYSA-N lufenuron Chemical compound C1=C(Cl)C(OC(F)(F)C(C(F)(F)F)F)=CC(Cl)=C1NC(=O)NC(=O)C1=C(F)C=CC=C1F PWPJGUXAGUPAHP-UHFFFAOYSA-N 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; 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
Definitions
- This invention relates to linear predictive coding.
- it is an improved method and means of determining coefficients for linear predictive coding.
- Linear predictive coding is a method of analyzing a speech signal and characterizing that signal in terms of coefficients which can be encoded, broadcast, received, and decoded to recover a close approximation to the original signal.
- the existence of redundancies in speech makes it possible to use encoded descriptions of the speech that can be carried in a communication channel having a bandwidth that is less than the bandwidth of the speech. This is in distinct contrast to many well-known forms of converting speech into digital signals. Most of these methods require a bandwidth that is greater than the bandwidth of the speech.
- Linear predictive coding (LPC) of speech begins conceptually with a model of the human speech-producing system.
- the model has a source of sound that is analogous to the vocal cords. That source is coupled acoustically to a stacked array of hollow cylindrical tubes that is analogous to the cavities of the throat and mouth in a human speaker.
- speech is characterized by four types of quantities. The first of these is a measure of whether speech is voiced or unvoiced.
- a voiced signal begins with an input from the vocal cords, while an unvoiced signal is produced by the action of the rest of the vocal tract on moving air alone. This produces the differences in sound between "s" which is unvoiced and its voiced equivalent "z", for example.
- a second characteristic of the sound is the pitch, the fundamental frequency produced by the vocal cords in making a voiced sound.
- a third characteristic is the energy.
- the effect of the throat and mouth on either voiced or unvoiced sound is summarized by obtaining some measure of the transfer function of the vocal tract. Such a measure might be the reflection coefficients of the structure, the poles of the transfer function of the structure, the logarithmic area ratios (LAR's) of the structure, or any of several other well-known functions of such resonances.
- various mathematical transforms of these functions may have utility for particular purposes. The functions are interrelated so that any one set can be determined from a knowledge of any other set.
- the present invention is an improved method and means of determining quantities corresponding to reflection coefficients.
- the reflection coefficients are coefficients with a specific all pole filter structure known as a lattice filter.
- the reflection coefficients discussed here are the electrical analog of acoustical reflection coefficients. While the reflection coefficient is in general a complex quantity in which the imaginary portion is a measure of loss at a discontinuity, when determining the reflection coefficients that characterize a human vocal tract, the portions of reflection coefficients associated with loss are small enough compared to the real part that denotes lossless reflection that it is adequate to use a lossless model in which the reflection coefficients are real.
- One way of obtaining the reflection coefficients that characterize a sample of a signal such as speech is to determine the characteristics of an inverse lattice filter that will reproduce the signal when excited by an impulse. Examples of several approaches of performing such an analysis are given in an article entitled “Stable and Efficient Lattice Methods for Linear Prediction” by Makhoul in “IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. ASSP-25, No. 5, October, 1977. This article points out that an analysis based on the all-pole lattice filter is stable without windowing but at a computational cost that is several times the cost of the auto-correlation and covariance methods of calculation. What Makhoul refers to as the computational costs of computer analysis are proportional to the equipment costs of realizing a circuit for comparable analysis on a semiconductor chip.
- An improved method and means of determining reflection coefficients that characterize an electrical signal obtains characteristics of an all-zero inverse lattice filter.
- the reflection coefficients are obtained by filtering the signal, sampling the filtered signal. obtaining the elements of a correlation matrix from the samples, initializing values of matrices of forward residual autocorrelations, backward residual autocorrelations, and cross correlation of residuals, combining matrix elements to obtain a first reflection coefficient, removing from the forward, backward and cross-correlation matrices the effect of the first reflection coefficient, calculating from the revised matrices a second reflection coefficient, and repeating the calculations to the desired order.
- Fig. 1 is an overall block diagram of a circuit for the practice of the present invention.
- Fig. 2 is an expanded circuit diagram of the address calculator of Fig. 1.
- Fig. 3 is an expanded circuit diagram of the update calculator of Fig. 1.
- Fig. 4 is an expanded circuit diagram of the reflection-coefficient calculator of Fig. 1.
- Fig. 5 is a flowchart of a method for practicing the invention.
- Fig. 6 is a block diagram of a section of a typical lattice filter for the practice of the present invention.
- Fig. 1 is an overall block diagram of a circuit for the practice of the invention.
- an electrical analog signal that is to be analyzed is applied at terminal 10. That signal will typically be an electrical analog of a voice signal, although it may be any electrical signal that exhibits redundancies analogous to those of speech. Examples of such other signals include video scans and seismic analysis records.
- the signal at terminal 10 is applied to a filter 12, if necessary, to limit its bandwidth. If the bandwidth is already adequate, filter 12 may comprise a direct wire connection, or filter 12 may combine a bandpass filter with any of a number of systems of pre-emphasis that are commonly used in radio broadcasting.
- ADC analog-to-digital converter
- the digital output of ADC 14 will be separated into frames of a convenient length, of the order of tens of milliseconds. That function is here indicated as being performed by framer 16 as a means of insuring that the digital input to correlator 18 establishes correlation among samples in the same frame.
- the function of framer 16 could also be combined into correlator 18 or ADC 14. It should be noted that the ADC 14 is not necessary if the signal is already in digital form.
- the correlation parameters are obtained in the circuit of Fig. 1 because that circuit will be used to determine reflection coefficients.
- the output of correlator 18 is applied, if necessary, to a normalizer 20 to normalize output values to a common level.
- the output of normalizer 20 is taken to random-access memory (RAM) 22 where it is stored in an address that is directed by a signal from multiplexer 23.
- Normalizer 20 also generates a signal indicating the completion of the operation of correlator 18 for one frame. That signal is taken as an input to sequencer 24. Signals from sequencer 24 are coupled out to control an address calculator 26, an update calculator 28, a reflection coefficient calculator 30, multiplexer 23, and multiplexer 32. Normalizer 20 determines the appropriate addresses in RAM 22 for storing the coefficients of a correlation matrix so that their serial readout will be in a desired order.
- the output of normalizer 20 is applied to multiplexer 23 to apply first an initial condition to RAM 22 that is determined from normalizer 20, and then accessed by address instructions from address calculator 26.
- the output of RAM 22 is applied through multiplexer 32 to RAM 34.
- Multiplexer 32 selects as an input to RAM 34 either the output of RAM 22 or the output of update calculator 28.
- Multiplexer 32 is controlled by a signal from sequencer 24.
- the location of storage elements in RAM 34 is controlled by a signal from address calculator 26.
- the output of RAM 34 is read into update calculator 26 and reflection coefficient calculator 30.
- update calculator 28 also receives as an input the calculated reflection coefficients from reflection coefficient calculator 30, which coefficients are taken as the output of the circuit of Fig. 1.
- Fig. 2 is a circuit diagram of the address calculator 26 of Fig. 1.
- Address calculator 26 produces the addresses that direct the retrieval of matrix elements in RAMs 22 and the storage and retrieval of matrix elements in RAM 34.
- sequencer 24 supplies addresses to read-only memory (ROM) 40.
- ROM 40 is read out into multiplexers 42 and 44.
- the output of multiplexer 42 is taken to RAM 46 which is loaded under the control of signals from sequencer 24.
- the output of RAM 46 is taken directly as the input to RAM 34 of Fig. 1, and it is also applied to latches 48 and 50, as well as the add/subtract unit 42.
- the output of latch 48 is taken to multiplexer 23 of Fig. 1, and then to RAM 22.
- the output of latch 50 is multiplexed in multiplexer 44 with the output of ROM 40 under the control of a signal from sequencer 24.
- the output of multiplexer 44 is applied to add-subtract unit 52 where it is supplied as an input to be either added or subtracted from the output of RAM 46, depending upon a control signal from sequencer 24.
- the add/subtract unit 52 also has an output connected to sequencer 24 which indicates a zero result from the add/subtract operation.
- Fig. 3 is a circuit diagram of the update calculator 28 of Fig. 1.
- data inputs are applied at terminals 60 and 62.
- the input at terminal 60 is the output of RAM 34 of Fig. 1.
- Terminal 60 is connected to a shifter 64, the output of which is taken to a RAM 66 and to a multiplexer 68.
- the output of RAM 66 is taken to multiplexer 70 which, in turn, is connected to multiplier 72.
- the output of multiplier 72 is taken as an input to multiplexer 68, as an input to register 74, and as an input to multiplexer 76.
- the output of register 74 is coupled through multiplexer 78 to supply a second input to multiplier 72.
- Terminal 62 is connected to reflection-coefficient calculator 30 of Fig.
- OR gate 90 The output of OR gate 90 is taken to register 92 which supplies an output that is taken both as a second input to OR gate 90 and as an input to priority encoder 94.
- the output of priority encoder 94 controls register 96 that operates shifter 64.
- the combination of shifter 64, register 96, OR gate 90, register 92 and priority encoder 94 comprises a normalizer that normalizes the output of RAM 34 of Fig. 1. If it is not desired or is considered unnecessary to normalize coefficients, then terminal 60 can supply an input directly to RAM 66 and the elements just described could be removed from the circuit of Fig. 3.
- Fig. 4 is a circuit diagram of the reflection coefficient calculator 30 of Fig. 1. In Fig.
- 4 terminal 100 receives a signal from RAM 34 that is applied to a subtractor 102 and a multiply-by-two circuit 104.
- the output of subtractor 102 is connected to register 106, which produces one output that is connected as a input to subtractor 102, and another output that is taken to divider 108.
- the output of divider 108 may be taken directly as a reflection coefficient.
- the signal at terminal 112 is a reflection coefficient of the equivalent filter of the original input signal.
- the reflection coefficients may be used directly as the coefficients in LPC or they may be transformed into a different function, as described earlier.
- Fig. 1 If it is desired to convert reflection coefficients into LAR's, this can be combined readily with the quantization that is performed by quantizer 110.
- the choice of the particular functions is one of design.
- Filter 12 has already been described as optional. If the circuit of Fig. 1 is to be applied to speech for use in a typical radio speech bandwidth, then the input signal may need to be subjected to bandpass filtering. It may also be desirable to combine some form of pre-emphasis with filter 12. Filter 12 may also be used to prevent aliasing when the filtered signal is applied to ADC 14.
- the sample rate produced by ADC 14 is a design parameter.
- sampling theorem it will be necessary to sample the input at a rate that is at least twice the frequency of the highest component contained in the input.
- sampling rates for speech are typically between 6.4 kHz and 10 kHz.
- Each sample is then encoded into a number of bits that typically ranges between 8 and 15, with 12 as a typical number. It follows that a typical frame will have of the order of one hundred samples.
- Correlator 18 takes these samples and determines from them the elements of a covariance matrix. This matrix is symmetric.
- p is the prediction order, a number that is typically between 8 and 12 for speech.
- the index k is kept less than or equal to i to avoid recalculating equal terms on both sides of the axis of the symmetric matrix.
- Normalizer 20 of Fig. 1 performs a function that is here indicated separately but that might also be included in correlator 18. Normalizer 20 shifts the elements of the correlation matrix so that the maximum value of any element in the array is between one-half and one in magnitude. Normalizer 20 then truncates the values of the elements thus shifted to a number of bits equal to the word length of the system.
- the covariance matrix thus has a number of elements equal to (p + 1) 2 .
- the covariance matrix is symmetric, it can be described completely by storing the elements of the diagonal and the elements below the diagonal, a total of (p + 1)(p + 2)/2 elements. These elements are stored in RAM 22 in a location that is controlled by address calculator 26. A convenient method of loading RAM 22 is to load the diagonal elements, beginning with the element of highest order and proceeding to the diagonal element of lowest order, and then repeat in sequence down paths in the matrix that are parallel to the main diagonal. It should be noted that the F and B matrices are also symmetric and may be stored in a similar fashion.
- an operations block 122 directs the determination of correlation coefficients. Such a determination is well known. For discrete or sampled components, it is normally accomplished by a calculation such as that of the following equation:
- the next step in the flowchart of Fig. 5 is to initialize the matrices of F, B and C as indicated in operations block 126.
- the quantities F, B and C are intermediate quantities used in the determination of LPC coefficients. Their initial values are determined as follows:
- Operations box 1 28 next directs that the value of j equal 1 .
- Operations box 1 30 then calls for the determination of the quantity k j , the jth reflection coefficient. This is determined as follows:
- Bj (i,k) B j-1 (i+l,k+1)+k j [C j-1 (i+l,k+1)+C j-1 (k+1,i+1)]+
- the value of j is increased by 1 in operations block 140, and control returns to operations block 130 to continue the calculations.
- Fig. 6 is a block diagram of a lattice filter that provides a further explanation of the process by which the circuit of Fig. 1 obtains reflection coefficients.
- a terminal 150 receives as an input the sampled signal. This signal is applied to an upper leg 152 which will calculate a forward residual, and it is applied to a lower leg 154 which will apply the signal to the first of a sequence of delay elements 156 to calculate a backward residual.
- Fig. 6 comprises a cascade of elements, each of which applies the forward signal to a multiplier 158 and a summer 165. The backward signals are applied to a multiplier 162 and a summer 164. Both multipliers 158 and 162 receive as additional inputs the current reflection coefficient. Thus, the current forward residual is multiplied by the current reflection coefficient and added to the current backward residual in summer 164 to generate as an output the next backward residual.
- the current backward residual is multiplied in multiplier 162 with the current reflection coefficient and added to the current forward residual in summer 160 to generate the next forward residual.
- the process just described continues through a number of sections of the lattice filter that is determined by the designer as a number adequate to characterize the particular signal in question. This is typically a number of stages equal to 8, 10 or 12. The last such stage is shown here as receiving a current forward residual signal on terminal 166 and a current backward residual signal on terminal 168.
- the current forward residual signal is applied to a multiplier 170 and a summer 172, while the current backward residual is delayed in delay element 174, and the delayed signal is applied to multiplier 176 and summer 178. Both multipliers 170 and 176 receive as additional inputs the current reflection coefficient.
- the result of applying a signal to this circuit of Fig. 6 is the production in forward line 152 of a sequence of elements of a forward residual vector and to produce in line 156 the elements of a backward residual vector. Individual elements are combined to produce an autocorrelation matrix of the forward residual elements, and autocorrelation matrix of the backward residual elements, and a cross-correlation matrix between forward and backward residual elements. These matrices are used as described earlier to calculate the reflection coefficients.
- Lattice methods of determining coefficients for linear predictive coding have been used in the past.
- circuits and programs used to determine the lattice coefficients have used intermediate variables that varied in magnitude over a wide range. This required a wide range of quantize values to characterize the intermediate variables, and thus took more computational time.
- the circuit arrangement and method of the present invention uses only variable and intermediate variables which are bounded in magnitude by unity. This permits operations and calculations to be performed in a fixed-point fractional implementation.
- the input signal is windowed so that it is stationary in a statistical sense, then it can be shown that the number of computations necessary. to determine lattice coeficients is reduced still further.
- the method and means of the present invention has been used with a frame length of approximately 15 milloseconds to determine 12 lattice coefficients in real time. By completing the calculations for the data of one frame before the end of the next succeeding frame. What is claimed is:
- NP MIN0(NP,KK-1) .
- AK( II ) QU(AK( II) , II,AR) C SEE IF DONE
- FR(I1,I2) FR(I1,I2)+ 1Z*(CR(I1,I2)+CR(I2,I1))+ZS*BR(I1,I2)
- BR(I1,I2) BR(I1+1,I2+1)+ 1Z*(CR(I1+1,I2+1)+CR(I2+1,I1+1))+ZS*FR(I1+1,I2+1)
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Health & Medical Sciences (AREA)
- Audiology, Speech & Language Pathology (AREA)
- Computational Linguistics (AREA)
- Physics & Mathematics (AREA)
- Signal Processing (AREA)
- Acoustics & Sound (AREA)
- Human Computer Interaction (AREA)
- Compression, Expansion, Code Conversion, And Decoders (AREA)
- Medicines Containing Material From Animals Or Micro-Organisms (AREA)
- Investigating Or Analysing Biological Materials (AREA)
- Ultra Sonic Daignosis Equipment (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
- Filters That Use Time-Delay Elements (AREA)
- Radar Systems Or Details Thereof (AREA)
- Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT84900575T ATE36206T1 (en) | 1983-01-03 | 1983-12-22 | IMPROVED METHOD AND MEANS FOR DETERMINING COEFFICIENTS FOR LINEAR PREDICTIVE CODING. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US45492983A | 1983-01-03 | 1983-01-03 | |
US454929 | 1983-01-03 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0135512A1 EP0135512A1 (en) | 1985-04-03 |
EP0135512A4 true EP0135512A4 (en) | 1985-06-10 |
EP0135512B1 EP0135512B1 (en) | 1988-08-03 |
Family
ID=23806651
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP84900575A Expired EP0135512B1 (en) | 1983-01-03 | 1983-12-22 | Improved method and means of determining coefficients for linear predictive coding |
Country Status (9)
Country | Link |
---|---|
EP (1) | EP0135512B1 (en) |
JP (1) | JPS60500274A (en) |
AT (1) | ATE36206T1 (en) |
AU (1) | AU566370B2 (en) |
DE (1) | DE3377599D1 (en) |
DK (1) | DK417184A (en) |
FI (1) | FI843448A (en) |
NO (1) | NO843498L (en) |
WO (1) | WO1984002814A1 (en) |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1318985A (en) * | 1970-02-07 | 1973-05-31 | Nippon Telegraph & Telephone | Audio response apparatus |
GB2026289B (en) * | 1978-04-12 | 1982-04-21 | Secr Defence | Self-adaptive linear prediction filters |
JPS597120B2 (en) * | 1978-11-24 | 1984-02-16 | 日本電気株式会社 | speech analysis device |
JPS55164700U (en) * | 1979-05-14 | 1980-11-26 | ||
JPS5853358B2 (en) * | 1980-03-31 | 1983-11-29 | 株式会社東芝 | speech analysis device |
US4378469A (en) * | 1981-05-26 | 1983-03-29 | Motorola Inc. | Human voice analyzing apparatus |
-
1983
- 1983-12-22 EP EP84900575A patent/EP0135512B1/en not_active Expired
- 1983-12-22 WO PCT/US1983/002038 patent/WO1984002814A1/en active IP Right Grant
- 1983-12-22 DE DE8484900575T patent/DE3377599D1/en not_active Expired
- 1983-12-22 AU AU24391/84A patent/AU566370B2/en not_active Ceased
- 1983-12-22 JP JP84500731A patent/JPS60500274A/en active Pending
- 1983-12-22 AT AT84900575T patent/ATE36206T1/en not_active IP Right Cessation
-
1984
- 1984-08-31 DK DK417184A patent/DK417184A/en not_active Application Discontinuation
- 1984-09-03 FI FI843448A patent/FI843448A/en not_active Application Discontinuation
- 1984-09-03 NO NO843498A patent/NO843498L/en unknown
Non-Patent Citations (2)
Title |
---|
COMPCON 79 (19TH IEEE COMPUTER SOCIETY INTERNATIONAL CONFERENCE), Washington, D.C., 4th-7th September 1979, pages 203-206, IEEE, New York, US; A.J. GOLDBERG et al.: "Microprocessor implementation of a linear predictive coder" * |
ICASSP 81 (IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING), Atlanta, 30th March - 1st April 1981, pages 355-353, IEEE, New York, US; F. SUGIYAMA et al.: "An LPC vocoder for efficient implementation" * |
Also Published As
Publication number | Publication date |
---|---|
JPS60500274A (en) | 1985-02-28 |
NO843498L (en) | 1984-09-03 |
DK417184A (en) | 1984-10-04 |
DE3377599D1 (en) | 1988-09-08 |
DK417184D0 (en) | 1984-08-31 |
AU566370B2 (en) | 1987-10-15 |
ATE36206T1 (en) | 1988-08-15 |
EP0135512B1 (en) | 1988-08-03 |
AU2439184A (en) | 1984-08-02 |
FI843448A0 (en) | 1984-09-03 |
WO1984002814A1 (en) | 1984-07-19 |
EP0135512A1 (en) | 1985-04-03 |
FI843448A (en) | 1984-09-03 |
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