Showing papers on "Codebook published in 1991"

On the performance and complexity of channel-optimized vector quantizers

Abstract: The performance and complexity of channel-optimized vector quantizers are studied for the Gauss-Markov source. Observations on the geometric structure of these quantizers are made, which have an important implication on the encoding complexity. For the squared-error distortion measure, it is shown that an operation equivalent to a Euclidean distance measurement with respect to an appropriately defined set of points (used to identify the encoding regions) can be used to perform the encoding. This implies that the encoding complexity is proportional to the number of encoding regions. It is then demonstrated that for very noisy channels and a heavily correlated source, when the codebook size is large, the number of encoding regions is considerably smaller than the codebook size-implying a reduction in encoding complexity. >

Method and apparatus for low-delay celp speech coding and decoding

Abstract: A low-bitrate (typically 8 kbit/s or less), low-delay digital coder and decoder based on Code Excited Linear Prediction for speech and similar signals features backward adaptive adjustment for codebook gain and short-term synthesis filter parameters and forward adaptive adjustment of long-term (pitch) synthesis filter parameters. A highly efficient, low delay pitch parameter derivation and quantization permits overall delay which is a fraction of prior coding delays for equivalent speech quality at low bitrates.

16 kbps wideband speech coding technique based on algebraic CELP

Abstract: The application of algebraic code excited linear prediction (ACELP) coding to wideband speech is presented An algebraic codebook with a 20 bit address can be used without any storage requirements and, more importantly, with a very efficient search procedure which allows for real-time implementation The authors describe an efficient procedure for searching such a large codebook deploying a focused search strategy, where less than 01% of the codebook is searched with performance very close to that of a full search High-quality speech at a bit rate of 13 kbps was obtained >

A fast nearest-neighbor search algorithm

Abstract: A fast nearest-neighbor search algorithm is developed which incorporates prior information about input vectors. The prior information comes in the form of a vector from the codebook which is known to be near the input vector, though it may not be the nearest codebook vector. A number of applications are described for which such prior information is available. The algorithm has a very simple structure and can be designed to have very low memory requirements. The new algorithm requires much less computation for constructing precomputed tables than previously proposed algorithms with comparable performance. Simulations show dramatic saving over conventional full search methods. >

Automatic language recognition using acoustic features

Abstract: Two language recognition algorithms are proposed and some experimental results are described. While many studies have been done concerning the speech recognition problem, few studies have addressed the language recognition task. The speech data used contains 20 languages: 16 sentences uttered twice by 4 males and 4 females. The duration of each sentence is about 8 seconds. The first algorithm is based on the standard vector quantization (VQ) technique. Every language is characterized by its own VQ codebook. The second algorithm is based on a single universal (common) VQ codebook for all languages, and its occurrence probability histograms. Every language is characterized by a histogram. The experiment results show that the recognition rates for the first and second algorithms were 65% and 80%, respectively, each using just 8 sentences of unknown speech (about 64 seconds). >

Geometric vector quantization

Abstract: A geometric vector quantizer coding technique is illustrated in the context of a full motion video coder based on a three-dimensional sub-band framework. The original image data is decomposed into different spatial-temporal frequency bands and based on the data in each band, different quantization strategies are applied to the bands. The lowest spatial-temporal frequency band is coded using a traditional three-dimensional switched predictor and optimum scaler quantizer. The non-dominant sub-bands are coded using the vector quantization approach to efficiently encode the images while appropriately exploiting the sparse, highly structured nature of the data to design the codebooks. Variable resolution is achieved using these techniques and no training is needed to establish or maintain the codebook. A fast codebook search technique is provided for identifying the optimal codebook vector for representing a block of input data. Examples of two and three level geometric vector quantizers are also provided.

A better tree-structured vector quantizer

Abstract: A new vector quantizer permits logarithmic-time encoding and yet performs better than the locally optimal quantizers generated by the LBG algorithm. The success is credited to an elaborated tree-structured optimization process in the codebook design. >

Speech coding and decoding system

Abstract: A speech coding and decoding system, the system is operated under a known code-excited linear prediction (CELP) coding method. The CELP coding is achieved by selecting an optimum pitch vector P from an adaptive codebook and the corresponding first gain, and at the same time, selecting an optimum code vector from a stochastic codebook and the corresponding second gain. The system of the present invention is featured by a weighted orthogonalization transforming unit introduced therein. The perceptually weighted code vector AC is not used as is, as usual, but after the transformation thereof into a perceptually weighted code vector AC' by the above unit; the vector AC' being made orthogonal to the optimum perceptually weighted pitch vector AP.

Speaker adaptation and voice conversion by codebook mapping

Abstract: The authors summarize a speaker adaptation algorithm based on codebook mapping from one speaker to a standard speaker. This algorithm has been developed to be useful in various kinds of speech recognition systems such as hidden-Markov-model-based, feature-based, and neural-network-based systems. The codebook mapping speaker adaptation algorithm has been much improved by introducing several ideas based on fuzzy vector quantization. This fuzzy codebook mapping algorithm is also applicable to voice conversion between arbitrary speakers. >

A content-addressable memory architecture for image coding using vector quantization

Abstract: An architecture suitable for real-time image coding using adaptive vector quantization (VQ) is presented. This architecture is based on the concept of content-addressable memory (CAM), where the data is accessed simultaneously and in parallel on the basis of its content. VQ essentially involves, for each input vector, a search operation to obtain the best match codeword. A speedup results if a CAM-based implementation is used. This speedup, coupled with the gains in execution time for the basic distortion operation, implies that even codebook generation is possible in real time ( >

Image compression method and apparatus employing distortion adaptive tree search vector quantization

Abstract: A variable rate vector quantization method employs a tree structured codebook. The level of the codebook from which codevectors are selected is determined by a threshold. The threshold varies according to the fullness of a buffer which stores vector quantized data to be transmitted.

Constrained-storage quantization of multiple vector sources by codebook sharing

Abstract: A codebook sharing technique, called constrained storage vector quantization (CSVQ), is introduced. This technique offers a convenient and optimal way of trading off performance against storage. The technique can be used in conjunction with tree-structured vector quantization (VQ) and other structured VQ techniques that alleviate the search complexity obstacle. The effectiveness of CSVQ is illustrated for coding transform coefficients of audio signals with multistage VQ. >

Image compression method and apparatus employing distortion adaptive tree search vector quantization with avoidance of transmission of redundant image data

Abstract: A variable rate vector quantization apparatus and method employs a tree structured codebook. Code vectors are selected from different levels of the codebook according to the value of a threshold. The value of the threshold is periodically adjusted according to the fullness of a buffer that stores vector quantized data to be transmitted. According to the invention, vector quantized data for redundant, or similar, vectors is not transmitted. Rather, a "copy last vector" instruction is transmitted for these vectors to achieve further data compression. A method of mean removal from vectors to be vector quantized is also disclosed.

Pitch sharpening for perceptually improved CELP, and the sparse-delta codebook for reduced computation

Abstract: The authors introduce two techniques for improving low-bit-rate CELP (code excited linear prediction) speech coders. The sparse-delta stochastic codebook is a recursive codebook design which can be searched using roughly 5% of the computational load required to search a full Gaussian codebook. Pitch sharpening is a class of algorithms which attempt to improve the perceptual quality of CELP by limiting the feedback of low-amplitude noiselike information to the adaptive codebook. Simulation results are presented for sparse-delta, ternary sparse-delta, and simplified-search sparse-delta coders, and for reduced-gain and sparse-adaptive-codebook pitch sharpening algorithms. >

Method of and apparatus for generating auxiliary information for expediting sparse codebook search

Abstract: In many applications involving the coding and processing of speech signals the relevant applicable codebook is one which may be termed a sparse codebook. That is, the majority of elements in the codebook are zero valued. The searching of such a sparse codebook is accelerated in accord with the present invention by generating auxiliary information defining the sparse nature of the codebok and using this information to assist and speed up searches of the codebook. In a particular method of searching the calculation of the distance between a target vector and a stored codebook vector is enhanced by use of a distortion metric derived from energy terms and correlation terms of the codebook entries. Calculation of these energy and correlation terms is speeded up by exploiting the sparseness of the codebook entries. The non-zero elements (NZE) of the space codebook are each identified and are defined by their offset from a reference point.

A method of, and system for, coding analogue signals

Abstract: In a Code Excited Linear Prediction (CELP) analogue signal coding system sequences from a master codebook (40), which may be a one dimensional codebook, are filtered (42) and then stored in slave codebooks (70, 72). Input analogue signals (20) are filtered (34, 36) and compared orthogonally (66, 78, 80) with sequences from the slave codebooks and an optimum pair of sequences are selected. Since the comparisons are orthogonal, sequences can be selected from the codebooks (70, 72) and compared (78, 80) with the filtered incoming analogue signals entirely independently. Reduced length sequences from the master codebook may be compared with orthogonalised analogue signals since orthogonalised signals contain some redundancy. The master codebook may not need to be orthogonalised in some circumstances. Various means of orthogonalisation of the sequences are possible including separation into odd and even sequences. Further orthogonalisations are possible, for example to give four comparisons.

Fine-coarse vector quantization

Abstract: A fast method for searching an unstructured vector quantization (VQ) codebook is introduced and analyzed. The method, fine-coarse vector quantization (FCVQ), operates in two stages: a 'fine' structured VQ followed by a table lookup 'coarse' unstructured VQ. Its rate, distortion, arithmetic complexity, and storage are investigated using analytical and experimental means. Optimality condition and an optimizing algorithm are presented. The results of experiments with both uniform scalar quantization and tree-structured VQ (TSVQ) as the first stage are reported. Comparisons are made with other fast approaches to vector quantization, especially TSVQ. It is found that when rate, distortion, arithmetic complexity, and storage are all taken into account, FCVQ outperforms TSVQ in a number of cases. In comparison to full search quantization, FCVQ has much lower arithmetic complexity, at the expense of a slight increase in distortion and a substantial increase in storage. The increase in mean-squared error (over full search) decays as a negative power of the available storage. >

Efficient codebook search for CELP vocoders

Abstract: A new way of determining correlation coefficients for stochastic codebook vectors for CELP coding of speech takes advantage of the sparsely populated nature of stochastic codebook vectors. N valued input signals (e.g., convolution vectors) to be correlated with N valued codebook vectors are fed to an N by N multiplexer or other selection means and the signal values either passed to an accumulator or not according to the state of N select inputs or other identification means determined from a memory store (e.g., an EPROM) whose entries correspond to the non-zero values of the codebook vectors. The accumulator output is the correlation of the codebook vector with the input signal. A sequencer steps through the entire codebook to provide correlation values for each vectors. The results are used to determine the optimum stochastic codebook vector for replicating the particular speech frame being analyzed.

CELP vocoder with efficient adaptive codebook search

Abstract: A new method for Code Excited Linear Predictive (CELP) coding of speech reduces the computational complexity by removing a convolution operation from a recursive loop used to poll the adaptive code book vectors. In a preferred embodiment, an impulse function of a short term perceptually weighted filter is first convolved with perceptual weighted target speech and the result cross-correlated with each vector in the codebook to produce an error function. The vector having the minimum error function is chosen to represent the particular speech frame being examined.

Fast algorithm for vq codebook design

Abstract: The paper presents a fast codebook training algorithm for vector quantisation. It uses an elimination rule, based on triangular inequality criteria, as well as the partial distortion elimination method, to relieve the computational burden of a conventional codebook training algorithm, including a binary codeword splitting algorithm for the initial codebook and the LBG recursive algorithm. Over 95%savings in both multiplication and addition operations were achieved in the simulation of a VQ codebook training of a ‘Lena’ image using 16-dimensional vectors.

Speech coding system having codebook storing differential vectors between each two adjoining code vectors

Abstract: A speech coding system is provided where input speech is coded by finding via an evaluation computation a code vector giving a minimum error between reproduced signals obtained by linear prediction analysis filter processing, simulating speech path characteristics, on code vectors successively read out from a noise codebook storing a plurality of noise trains as code vectors and an input speech signal and by using a code specifying the code vector. In the speech coding system, the noise codebook includes a delta vector codebook which stores an initial vector and a plurality of delta vectors having difference vectors between adjoining code vectors. In addition, provision is made in the computing unit for the evaluation computation of a cyclic adding unit for cumulatively adding the delta vectors to virtually reproduce the code vectors.

Speech decoder for high quality reproduced speech through interpolation

Abstract: A speech decoder includes a separating circuit, an error correction decoding circuit, an interpolating circuit, and a speech reproducing circuit. The separating circuit separates a code string of a filter parameter, a code string of a parameter associated with a pitch, and a code string of a parameter associated with an index and a gain of a codebook representing an excitation signal of speech from a received code string. The error correction decoding circuit detects a transmission error, which cannot be corrected, in the received code string. When a transmission error which cannot be corrected is detected, the interpolating circuit interpolates between parameters of past and future proper frames, thereby recovering parameters of a current frame. The speech reproducing circuit reproduces a speech signal on the basis of the interpolated parameters and other received codes.

Voice controlled pager and programming techniques therefor

Abstract: An individual desiring to operate a pager via voice commands sends a message to a repository of voice recognition codebooks requesting access to a particular codebook. The repository device(s) respond by transmitting the codebook of that individual to at least one pager, which stores the codebook therein. In a second embodiment, each individual operating a pager by voice commands is provided with a codebook module, which contains suitable memory storage having at least that operator's codebook stored therein. By inserting the codebook module (or card) into the pager, that pager becomes at least partially controllable by the voice commands of that operator. The codebook module may be easily removed to permit the communication device to be rapidly reprogrammed by inserting the codebook of another operator.

Backward Adaptive Configurations for Low-Delay Vector Excitation Coding

Abstract: Many of the advances in speech coding in the past decade at rates of 48–16 kbit/s have been based on excitation coding by means of analysis-by-synthesis Excitation coding schemes have a decoder structure consisting of an excitation signal applied to a time-varying synthesis filter to produce the reconstructed, or “synthesized,” output speech In addition to other tasks, the encoder must determine a suitable excitation signal and transmit data that specifies this excitation In the analysis-by-synthesis technique, the excitation is selected by a closed-loop search procedure where a candidate excitation signal segment is applied to the synthesis filter, the synthesized waveform is compared with the original speech segment, the distortion is measured, and the process is repeated for all excitation segments stored in an excitation codebook The index of the “best” excitation segment is transmitted to the decoder, which retrieves the excitation segment from a codebook identical to that at the encoder The parameters of the synthesis filter are computed using well-known linear prediction analysis techniques on a frame of buffered input samples and transmitted to the decoder This coding scheme is often called Vector Excitation Coding (VXC) or Code Excited Linear Prediction (CELP) [1,2]

Progressive transmission of vector quantized data

Abstract: A distortion adaptive vector quantization method is employed to select, for each input vector, several codevectors from a tree structured codebook. The first codevector defines a basis signal, and each subsequent codevector defines an enchancement signal. The basic signal is indicative of the full codebook address from which the first codevector was selected. Each enhancement signal is indicative of only so much of the additional address bits that are required, in combination with the basic signal, to identify the address of the codebook from which the subsequent codevectors were selected. The basic signal and each enhancement signal are transmitted to a decoder which may employ only the basic signal, or the basic signal and one or more of the enhancement signals to reproduce the input vector. The reproduction quality of the input vector increases with the number of enhancement signals chosen.

Image sequence coding using adaptive tree-structured vector quantization with multipath searching

Abstract: A new adaptive tree-structured vector quantization (adaptive TSVQ) with multipath searching is described. The structure of the codebook tree is reorganized at an update interval, without requiring any transmission of side information. The 1-path tree searching algorithm is the simple way to find the closest codeword in TSVQ. But the disadvantage of 1-path searching is that the selected codeworks are not, in general, closest to the input vectors. Hence, the authors propose the multipath searching algorithm to improve the image quality. In an experiment, the improvement over the fixed TSVQ at the same bit rate is up to 2.03 dB when the number of the leaves in the codebook tree is 256 and 4-path searching is applied. >

Efficient Encoding of the Long-Term Predictor in Vector Excitation Coders

Abstract: Speech coding algorithms based on Code-Excited Linear Prediction (CELP) [1], have been widely studied in the past few years for low bit rate speech coding and many improvements and variations of the basic algorithm have since emerged. We use Vector Excitation Coding (VXC) as a generic name to represent the class of coders using vector quantization (VQ) coding of filtered excitation signals with “closed-loop” codebook search [2, 3].

Constrained-storage vector quantization in high fidelity audio transform coding

Abstract: The concept and design methods for efficient use of vector quantization (VQ) in high-fidelity audio coding are presented. It is demonstrated that with constrained-storage VQ (CSVQ), tree-structured codebooks can be constructed for very high rates without incurring an exponential growth in storage complexity and without impairing the rate-distortion performance. Nonlinear interpolative VQ allows efficient coding of the power envelope needed for transform-coefficient normalization and adaptive distortion assignment. These techniques lead to a substantial reduction in the overall bit rate and codebook storage for the audio coder. >

Maximum descent method for image vector quantisation

Abstract: An efficient codebook design algorithm for image vector quantisation is proposed. As compared with the LBG algorithm, the computation time in designing a codebook is being greatly reduced, and a significant improvement on the coding performance for both the picture inside and outside the training sequence is found.