Older video game consoles and home computers often generated a technically-compliant NTSC or PAL signal (480i and 576i respectively) but only sent one field type rather than alternating between the two. This created a 240 or 288 line progressive signal, which in theory can be decoded on any receiver that can decode normal, interlaced signals. Since the shadow mask and beam width of standard CRT televisions were designed for interlaced signals, these systems produced a distinctive fixed pattern of alternating bright and dark scan lines; many emulators for older systems offer video filters to recreate this effect.