现代高级组合音响,录音机单元常做成录音座的形式,而录音座的噪声主要来自磁带的固有噪声,磁带本身的噪声随频率增大而增大。如果在放音中衰减高频信号来提高S/N,势必损失节目中的信号成分。因此,为了做到既不破环节目源的频率特性又能提高S/N,必须采用特殊的互补方法,杜比系统就是这种特殊的互补型动态降噪系统。杜比系统的作用表现在录音和放音两个环节,录音时,输入信号分为主、副两个通道,主通道为原信号,副通道信号经过编码处理与主通道信号相加进行动态压缩后供录音;放音时,副通道信号经反馈、解码进行动态扩展而输出原信号。杜比B(民用型,电路简单,价格纸)型压扩作用仅在小信号的高频段进行,降噪量可达10dB。杜比-HX(headroom ex-pansion)即“动态余量扩展器”,克服了旧偏磁方式存在的问题,使任何频率的信号都提供理想的偏磁电平。作者设计的双卡录音座电路具有杜比B和杜比-HX功能,录音座采用交流抹音和交流偏磁,手控录音电平并有耳机监听输出及LEO电平指示。整机共用4块集成电路,并将录、放音电路分开,以简化电路。安装、调试后,各项指标均达到要求。 Modern high-level composite audio and tape recorder units are often made into a recording base. The noise of the recording base mainly comes from the inherent noise of the tape, and the noise of the tape itself increases with increasing frequency. If you attenuate high frequency signals during playback to increase S / N, you will inevitably lose the signal components in the program. Therefore, in order to improve the S / N without breaking the frequency characteristics of the source of the program, a special complementary method must be adopted, and the Dolby system is such a special complementary dynamic noise reduction system. The role of Dolby system performance in the recording and playback of two aspects, the recording, the input signal is divided into primary and secondary channels, the main channel is the original signal, the secondary channel signal is encoded and the main channel signal is added to the dynamic compression After recording; playback, sub-channel signal feedback, decode the dynamic expansion and output the original signal. Dolby B (civil, simple circuit, price paper) type companding effect only in the high frequency of small signals, noise reduction up to 10dB. The headroom ex-pansion (“headroom ex-pansion”) is a “headroom extender” that overcomes the problems of the old bias mode and provides a perfect bias level for any frequency signal. The author designed dual-card recording cradle circuit with Dolby B and Dolby-HX function, the recording base with AC wiping and AC bias, manual recording level and headphone monitor output and LEO level indication. Machine sharing 4 integrated circuits, and recording, playback circuit separate to simplify the circuit. After installation and commissioning, all the indexes have met the requirements.