The vast majority of the sound travels from the source to the destination, align the arrow in that manner and don't worry about the reverse. BTW, you won't hurt anything, so its ok to flip it and do a sound check. Example, if you are feeding a soundbar from the TV and using hdmi, align the arrow as sending out of the tv and into the soundbar. If you are going from a DVD to a soundbar via HDMI, align out of the dvd and into the soundbar. It's always "into" the box that is making the "noise".