Audio Electronics pdf

[...]... 346 11 Digital audio broadcasting Broadcasting system choices AM VHF FM Digital audio broadcasting Digital radio and TV: the growth of complexity Phase shift modulation systems Multiplex (MUX) systems Perceptual coding 352 352 352 352 353 354 355 355 356 349 Contents Avoidance of time delay distortion DAB transmitter and receiver layouts The NICAM-728 TV stereo sound system The NICAM-728 audio signal... Preface The progress of 'audio' towards the still-distant goal of a perfect imitation of reality has been, and remains, inextricably bound up with the development of electronic components and circuit technology, and with the parallel progress in the various transducers and interface devices used to generate and reproduce electrical signals However, while in the early years of audio almost all the development... which the designers make their designs has become increasingly analytical and theoretical in its nature This change is as inevitable as it is predictable since there are many parts of this work - digital audio, for example - which can no longer be designed by any pragmatic 'suck it and see' method, and whose undoubted success has been entirely dependent on the correct outcome of theoretical calculations... subsequently polished to improve tape/head contact and lessen head wear The preferred form of both ferric oxide and chromium dioxide crystals is needle-shaped, or 'acicular', and the best characteristic for audio tapes are given when these are aligned parallel to the surface, in the direction of magnetisation This is accomplished during manufacture by passing the tape through a strong, unidirectional magnetic... the lower end of the usable frequency range, the overall efficiency of the recording process, and the LF S/N ratio is somewhat improved The improvement is at the expense of some erasure of the higher audio frequencies, which increases the need for HF preemphasis to achieve a 'fiat' frequency response However, since it is Tape Recording 20 10 Fe Fe dB 0 : J ref 250 nW/m , , %THD -,'10 \ -,o.~ 9 ~:NNN,... will be greater, since there is almost invariably a decrease in permeability with increasing frequency This will require more care in the design of the recording head Typically, the chosen frequency for audio work will be between four and six times the highest frequency which it is desired to record" it will usually be in the range 60-120 kHz, with better machines using the higher values 21 Tape Recording... performance Also, it is vitally important that the HF 'bias' signal should have a very low noise component In the composite signal applied to the record head, the bias signal may be 10-20 times greater than the audio signal to be recorded If, therefore, the bias waveform is not to degrade the overall 22 Tape Recording S/N ratio of the system, the noise content of the bias waveform must be at least 40 times better... act, in part, as a bias waveform, so some recorders employ a monitoring circuit which adjusts the absolute value of the bias input, so that it is reduced in the presence of large HF components in the audio signal This can improve the HF response and HF output level for the same value of harmonic distortion in comparison with a fixed bias value system  .