Digital FM signal processing for VCRs

As CRTs have become larger, there has been an increasing demand for higher quality reproduced images from consumer VCRs that record FM signals. It is well known that the SNR is improved without deterioration of frequency response by using an equalizer to emphasize the lower sidebands or to suppress the upper sidebands of playback FM signals. However, a type of noise which appears as signal inversion is generated at black-to-white transitions. The SNR is therefore compromised by using a conventional equalizer to maintain the inversion margin. These equalizers have fixed characteristics, even for images without the transitions that cause signal inversions. We have applied digital signal processing technology to develop a dynamic equalizer that selects the optimum from among several equalizer functions at each sampling point, according to the state of the playback FM signal. Simulations have confirmed the improvement in SNR without causing inversions.