ffmpeg how do i know what audio rate to use?

[vpa021]

say i have something like this\[code\]ffmpeg -i video.avi -ar 22050 -ab 32 -f flv -s 320x240 video.flv -ar (Audio sampling rate in Hz)-ab (Audio bit rate in kbit/s)\[/code\]regarding the -ar and the -ab how do i know what rate to use? i got this ffmpeg command from a site somewhere and i was wondering how the person knew what values to put for the rates? do i have to understand audio in order to figure that out?thanks