A method of increasing the efficiency of a pulse-codemodulation communications system with time division of the channels by using the statistical properties of the speech signals is considered. The problems involved ...
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A method of increasing the efficiency of a pulse-codemodulation communications system with time division of the channels by using the statistical properties of the speech signals is considered. The problems involved in constructing such a system are discussed, its efficiency and noise immunity are determined and some theoretical results are given.
This paper examines quantization noise, harmonic and intermodulation distortion, and related power spectra encountered in PCM systems currently utilized in commercial telephony. Performance is evaluated as a function ...
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This paper examines quantization noise, harmonic and intermodulation distortion, and related power spectra encountered in PCM systems currently utilized in commercial telephony. Performance is evaluated as a function of quantization resolution for a number of bit rates, with emphasis on 7- and 8-bit PCM with sampling of speech and sinusoidal inputs at 8,000 Hz. Both uniform and nonuniform quantization are considered.
A DPCM system with adaptive quantization is described. Theoretical considerations on the optimum parameters that determine the quantizer adaptation in order to minimize the quantizing noise are developed. The performa...
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A DPCM system with adaptive quantization is described. Theoretical considerations on the optimum parameters that determine the quantizer adaptation in order to minimize the quantizing noise are developed. The performance of a 32 kbit/sec computer simulation of such a system is shown and the particular type of output quantizing noise examined. Attention is devoted to subjective evaluation of the output quality, even in presence of channel errors.
In transmission systems employing differential PCM (DPCM), errors accumulate at the receiver, making it necessary to transmit the whole value of the variable from time to time. Conversion of the value to be transmitte...
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In transmission systems employing differential PCM (DPCM), errors accumulate at the receiver, making it necessary to transmit the whole value of the variable from time to time. Conversion of the value to be transmitted to normalized form appears to diminish the effects of these errors. The normalized value must be expressed in terms of the limit towards which the signal tends. Reduction of the magnitude of the error is not instantaneous but depends on the signal level and signal fluctuations. In the case of constant level signals, there is no reduction, and the greater the signal amplitude and frequency, the quicker the reduction. Utilization of this coding method must be adapted to individual cases because the quantization interval varies with signal amplitude.
Difference-PCM (DIFPCM) is presented as a better scheme for digital encoding of highly correlated signals such as speech or TV. The optimum quantizers for speech and TV are developed using gamma and Laplace densities ...
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Difference-PCM (DIFPCM) is presented as a better scheme for digital encoding of highly correlated signals such as speech or TV. The optimum quantizers for speech and TV are developed using gamma and Laplace densities as approximations to the amplitude probability density of these signals, respectively. The speech used for these tests consisted of 72,000 samples of carefully selected words of English language. Theoretical and test results indicate that DIFPCM with optimum quantization provides a S/N gain of 6 dB for speech and 9 dB (expected) for TV over existing logarithmic ( mu equals 255) PCM. The measured DR of this DIFPCM is about 0. 6 of that for log-PCM. Theoretical and test results indicate that the performance of DIFPCM lies midway between that of PCM and differential PCM (DPCM).
A multiplex frame structure, which makes it possible to use economical hardware for high-speed operation is proposed, and the PCM hierarchy plan for the third to the fifth order following 1. 544-6. 312 Mb/s establishe...
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A multiplex frame structure, which makes it possible to use economical hardware for high-speed operation is proposed, and the PCM hierarchy plan for the third to the fifth order following 1. 544-6. 312 Mb/s established as 32. 064-97. 728-397. 20 Mb/s. This hierarchy is determined according to the following procedure. First, approximate digit rates are determined from the coding bit rates of various sources of information and the capacities of various transmission facilities. Second, the frame length is determined from the reframe time and the destuffing-error probability specifications. Third, exact digit rates are determined from the stuffing jitter and its suppression characteristics. This procedure can be applied universally to cases where a hierarchy must be revised or is originally planned.
A pseudo-random linear binary sequence with maximum length and high clock rate can be generated by multiplexing a certain number of phase-delayed replicas of this same sequence having a lower clock rate. The necessary...
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A pseudo-random linear binary sequence with maximum length and high clock rate can be generated by multiplexing a certain number of phase-delayed replicas of this same sequence having a lower clock rate. The necessary delays for the multiplexing of two or four sequences are determined. It is possible to realize all phase-delayed sequences by modulo-two-addition of the signals from appropriate outputs of the stages of a single shift register generator. By using a simple calculation procedure, the outputs which have to be used for a given structure of the generator can be determined.
The application of digital methods to the internal distribution of high-quality sound signals in a broadcasting system allows a high and predictable standard of technical quality to be maintained with the minimum of a...
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The application of digital methods to the internal distribution of high-quality sound signals in a broadcasting system allows a high and predictable standard of technical quality to be maintained with the minimum of attention by operating staff. pulse-code-modulation systems for the incorporation of a sound signal into a video waveform and for the multiplex distribution of programmes for the radio service will soon be in operation within the BBC, and the eventual use of national and international digital links for this purpose is envisaged. The feasibility of digital recording has also been demonstrated. This paper is mainly concerned with the special requirements to be met in the digital coding and decoding of broadcast-quality sound signals. Considerations of quantising noise, distortion and digit-error detection lead to a bit rate approaching half a megabit per second per channel, though this rate may be somewhat reduced as a result of current developments in digital companding. No attempt is made to deal with aspects of point-to-point transmission which are common to other digital systems, but the effects of digit-error rate and of timing jitter are considered, and tolerances are suggested.
Various techniques of active RC realisation of lowpass filters are discussed, and two methods which are considered to have engineering relevance are investigated in detail. The design of lowpass filters suitable for u...
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Various techniques of active RC realisation of lowpass filters are discussed, and two methods which are considered to have engineering relevance are investigated in detail. The design of lowpass filters suitable for use in f.d.m. and p.c.m. systems is presented. The results of tests carried out on microelectronics models of these filters show that they meet the requirements for use in practical systems.
Perchlormethyl mercaptan is a highly toxic volatile inhalation poison. A fatal case of PCM intoxication we point is described to draw attention to the risks of occupational exposure to PCM. We discuss the biochemical ...
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Perchlormethyl mercaptan is a highly toxic volatile inhalation poison. A fatal case of PCM intoxication we point is described to draw attention to the risks of occupational exposure to PCM. We discuss the biochemical and toxicological courses of various reactions to PCM, and also the pathomorphology of a fatal case of PCM intoxication. Additional safety measures for use with PCM are recommended from the viewpoint of social medicine.
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