DOI:10.1049/ree.1983.0012

出版商:IERE    

年代:1983

数据来源: IET

DOI:10.1049/ree.1983.0015

出版商:IERE    

年代:1983

数据来源: IET

摘要:

The purpose of this paper is partly tutorial, partly interrogative and partly speculative, the objective in each case being to provoke critical thought. Doubt is cast on common presumptions about the superiority of digital audio, and it is suggested that the most relevant properties have not been sufficiently well identified or evaluated. It is concluded that, so far, digital recording has at best marginal overall advantage over analogue, and is definitely inferior in some respects including dynamic range.Mutual competition between digital and analogue technologies is likely to stimulate improvements in audio standards during the next few years, and during this period the methods can complement each other. Digital techniques promise superior audio quality in the end, but only when formidable problems of analogue accuracy have been solved.Crucial harm may be done to the acceptance of digital sound by the assumption that digital methods are automatically better, or by a preoccupation with standardization at the expense of standards or performance. Premature standardization could stultify the development of digital audio for a long time to come.

DOI:10.1049/ree.1983.0016

出版商:IERE    

年代:1983

数据来源: IET

摘要:

A description is given of the eight to fourteen modulation system (EFM) designed for the Compact Disc Digital Audio System with optical read-out. EFM combines high information density and immunity to tolerances in the light path with low power at the low-frequency end of the modulation bit stream spectrum. In this modulation scheme, blocks of eight data input bits are transformed into fourteen channel bits, which follow certain minimum and maximum run-length constraints by using a code book. To prevent violation of the minimum and maximum run-length constraints a certain number of merging bits are needed to concatenate the blocks. There are cases where the merging bits are not uniquely determined by the concatenation rules. This freedom of choice thus created is used for minimizing the power of the modulated bit sequence at low frequencies. The paper presents the results of algorithms that were used to minimize this low frequency content.

DOI:10.1049/ree.1983.0017

出版商:IERE    

年代:1983

数据来源: IET

摘要:

This paper briefly considers existing information on universallogic- modules which may be used for the realization of functions of n≤3 independent input variables (‘ULM.3’), and their circuit realizations, and selects two candidates,f4andf5, as preferable choices for practical adoption. The synthesis of arbitraryn-variable functions using these candidates is then pursued, including the utilization of symmetries in the functions being synthesized.

DOI:10.1049/ree.1983.0018

出版商:IERE    

年代:1983

数据来源: IET

摘要:

The types of antenna array commonly used in the UK in conjunction with high-power h.f. transmitters and their principles of operation are outlined. Methods of predicting field strengths and power densities in both the near and far fields of such arrays are discussed. Particular reference is made to curtain arrays, log-periodic antennas, and rhombic antennas. Typical field strength patterns are illustrated for each type.An application is the prediction of the external radio frequency environment in which aircraft and flight weapons systems have to operate.

DOI:10.1049/ree.1983.0019

出版商:IERE    

年代:1983

数据来源: IET

摘要:

Linear superposition based on simple theory suggests that the improvement in linear bit density for the thin-film head is about 25% over its Karlquist counterpart. Dynamic iterative simulation via the Extended Dynamic Iterative Model (EDIM) concluded that a finite pole-width head is excellent for writing but poor as a read head due to limited low-frequency response,and the previous superposition prediction appears optimistic. A good combination would be a narrow polewidth for WRITE and a wide pole-width for READ. The criteria of linear and non-linear distortion for magnetic recording are reviewed, and a group of universal test patterns, capable of revealing worst-case peakshift and resolution independent of coding schemes, is proposed. The modelling technique of EDIM is briefly discussed with illustrations of the recording and demagnetizing distribution for in-depth analysis of the high-density digital recording process.

DOI:10.1049/ree.1983.0020

出版商:IERE    

年代:1983

数据来源: IET