A drawback of SECAM for production is that, unlike PAL or NTSC, certain post-production operations of encoded SECAM signals are not really possible without a significant drop in quality. As an example, a simple fade to black is trivial in NTSC and PAL: one merely reduces the signal level until it is zero. However, in SECAM the color difference signals, which are frequency modulated, need first to be decoded to e.g. RGB, then the fade-to-black is applied, and finally the resulting signal is re-encoded into SECAM. Because of this, much SECAM video editing was actually done using PAL equipment, then the resultant signal was converted to SECAM. Another drawback of SECAM is that comb filtering, allowing better color separation, is of limited use in SECAM receivers. This was not, however, much of a drawback in the early days of SECAM as such filters were not readily available in high-end TV sets before the 1990s.