If you have a Performa or Power Macintosh 5400 or 5500 and your monitor is set to a resolution of 640 x 480, make sure that your monitor is set at a frequency of 67Hz. If the frequency is reduced to 60Hz or lower, video output from the Avid Cinema card will appear to pulsate.
Note: At 640x480, 67Hz produces less flicker and is more pleasing to the eye, so this is what your monitor should be set to for general use.
To set the resolution and frequency of your monitor, open the Monitors & Sound control panel and select "640 x 480, 67Hz" in the Resolution box.
This article was published in the 13 June 1997 "Information Alley".