Noise is the enemy of all recording and communications systems, and in FM practice it is common to boost the HF components of the modulating signal prior to the modulation process, a process known as pre-emphasis, and so do we in VCR FM modulation circuits. The effect of this after demodulation (in the post-detector circuit of a radio or the playback amplifier of a VCR) is to give a degree of HF lift to the baseband signal. In removing this with a filter, gain is effectively reduced at the HF end of the spectrum, with an accompanying useful reduction in noise level. The idea is shown in Figure 21.11, which illustrates the filter characteristics in record and replay, along with the effect on the noise level.

Figure 21.11: The effect of pre-emphasis and de-emphasis on playback signal-to-noise (SNR) ratio