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  • 1
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    Application of a VLSI vector quantization processor to real-time speech coding (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Attention is given to a working vector quantization processor for speech coding that is based on a first-generation VLSI chip which efficiently performs the pattern-matching operation needed for the codebook search process (CPS). Using this chip, the CPS architecture has been successfully incorporated into a compact, single-board Vector PCM implementation operating at 7-18 kbits/sec. A real time Adaptive Vector Predictive Coder system using the CPS has also been implemented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-4; 112-124
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    4800 B/S speech compression techniques for mobile satellite systems (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper will discuss three 4800 bps digital speech compression techniques currently being investigated for application in the mobile satellite service. These three techniques, vector adaptive predictive coding, vector excitation coding, and the self excited vocoder, are the most promising among a number of techniques being developed to possibly provide near-toll-quality speech compression while still keeping the bit-rate low enough for a power and bandwidth limited satellite service.
    Keywords: COMMUNICATIONS AND RADAR
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Speech coding at 4800 bps for mobile satellite communications (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A speech compression project has recently been completed to develop a speech coding algorithm suitable for operation in a mobile satellite environment aimed at providing telephone quality natural speech at 4.8 kbps. The work has resulted in two alternative techniques which achieve reasonably good communications quality at 4.8 kbps while tolerating vehicle noise and rather severe channel impairments. The algorithms are embodied in a compact self-contained prototype consisting of two AT and T 32-bit floating-point DSP32 digital signal processors (DSP). A Motorola 68HC11 microcomputer chip serves as the board controller and interface handler. On a wirewrapped card, the prototype's circuit footprint amounts to only 200 sq cm, and consumes about 9 watts of power.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Jet Propulsion Lab., Proceedings of the Mobile Satellite Conference; p 485-490
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Performance of a low data rate speech codec for land-mobile satellite communications (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: In an effort to foster the development of new technologies for the emerging land mobile satellite communications services, JPL funded two development contracts in 1984: one to the Univ. of Calif., Santa Barbara and the other to the Georgia Inst. of Technology, to develop algorithms and real time hardware for near toll quality speech compression at 4800 bits per second. Both universities have developed and delivered speech codecs to JPL, and the UCSB codec was extensively tested by JPL in a variety of experimental setups. The basic UCSB speech codec algorithms and the test results of the various experiments performed with this codec are presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Proceedings of the 2nd International Mobile Satellite Conference (IMSC 1990); p 647-653
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  • 5
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    Gain-adaptive vector quantization for medium-rate speech coding (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A class of adaptive vector quantizers (VQs) that can dynamically adjust the 'gain' of codevectors according to the input signal level is introduced. The encoder uses a gain estimator to determine a suitable normalization of each input vector prior to VQ coding. The normalized vectors have reduced dynamic range and can then be more efficiently coded. At the receiver, the VQ decoder output is multiplied by the estimated gain. Both forward and backward adaptation are considered and several different gain estimators are compared and evaluated. An approach to optimizing the design of gain estimators is introduced. Some of the more obvious techniques for achieving gain adaptation are substantially less effective than the use of optimized gain estimators. A novel design technique that is needed to generate the appropriate gain-normalized codebook for the vector quantizer is introduced. Experimental results show that a significant gain in segmental SNR can be obtained over nonadaptive VQ with a negligible increase in complexity.
    Keywords: COMMUNICATIONS AND RADAR
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  • 6
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    Vector excitation coding with dynamic bit allocation (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Vector excitation coding (VXC) has shown promise for digital transmission of fairly high communications quality speech at low bit rates, but current version of the algorithm still suffer from audible degradations, particularly at 4.8 kb/s. The authors examine the technique of dynamic bit allocation (DBA) to improve the performance of VXC for a given bit rate. The approach is based on the observation that the minimum bit rate needed to code adequately both the long-term and short-term predictors in VXC varies dynamically with time. Therefore, in frames where fewer bits suffice for the predictors, the unneeded bits can be reallocated to other coder parameter sets such as excitation vectors. By dynamically distributing available bits among the different coder parameter sets while keeping the total number of bits in each frame fixed, it is possible to improve overall coder performance without increasing bit rate.
    Keywords: COMMUNICATIONS AND RADAR
    Type: GLOBECOM ''88 - IEEE Global Telecommunications Conference and Exhibition; Nov 28, 1988 - Dec 01, 1988; Hollywood, FL; United States
    Format: text
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