高保真(Hi-Fi)音响系统中,限制和改变重发声音质量的两个重要因素就是噪声和畸变。在声音最终为人耳所享受的前题下,噪声甚至比畸变更难于使人忍受。所以在高保真音响系统的设计中,最困难的,可能是它的噪声指标了。我们知道,只要第一级增益足够大则系统总的噪声系数将取决于第一级的噪声系数,即: Two important factors that limit and alter the quality of the reissued sound in Hi-Fi systems are noise and distortion. Under the premise that the sound is ultimately enjoyed by the human ear, the noise is even more difficult to endure than distortion. So the design of the hi-fi system, the most difficult, may be its noise figure. We know that as long as the gain of the first stage is large enough, the total noise figure of the system will depend on the noise figure of the first stage, namely: