SDTV can be broadcast in 704 pixels × 480 lines (16:9 and 4:3 ratios) or 640 pixels × 480 lines (4:3 ratio). The refresh rate can be any of 24, 30 or 60 pictures per second.

SDTV in 4:3 aspect ratio has the same appearance as the regular analogue TV (NTSC, PAL, PAL2, SECAM) minus the ghostly, snowy images and static noises.

Reference: [ATSC]