1 前言 声音广播的发展历程表明它是逐步发展的。早先,多数听众围坐在一部收音机周围收听调幅广播,由于收音机很大很重,需要由电网供电或由相当大的电池供电,所以收音机都是固定的,听众只能迁就收音机。那时很难设想收音机能随人行动的便携式收音机。后来虽然有了调频和立体声广播,但调频收音机也是固定式的。后来的高保真(Hi-Fi)收音 1 Introduction The history of sound broadcasting shows that it is evolving. Earlier, most listeners sat around a radio listening for AM broadcasting. Because the radio was large and heavy, powered by a grid or powered by a fairly large battery, the radios were fixed and the listeners could only accommodate the radios. At that time it was hard to imagine a portable radio with a radio that could move with people. Later, although there are FM and stereo radio, but the FM radio is also fixed. Later high-fidelity (Hi-Fi) radio