With Quasi-PAL *OFF*, NTSC discs are output as converted PAL 50Hz, for compatibility with older TVs (this may introduce some artefacts though). Quasi-PAL *ON* enables 60Hz output. This setting affects all outputs - RGB, composite and S-Video.
For best results you should have Quasi-PAL switched ON all the time, unless you find your TV can`t cope with the signal.
Mike