Isn't Line Level always the same?
No. There are two levels to be concerned with, -10dBV (unbalanced) and +4dBu (Balanced). No matter how hard I try, there is always going to be pro-gear mixed in with "residential" or "consumer" gear and "pro" gear where they are designed to work at line levels. As you can imagine, the -10dBV is lower in level than the +4dBu gear. It's more complicated than that, but we will stick to this explanation since there is no need to know more unless you are going to be designing gear.
It's most common for people to plug a -10dBV piece of equipment into a +4dBu mixer. The common complaint is that the signal is low and you have to turn up the gain to get a decent level which increases noise levels too. In the studio environment, we see this most often with keyboards and synths. A solution to this is to use a Line Level Shifter® from Ebtech®. Put the box by your keyboard, plug in the 1/4" keyboard output into the Line Level Shifter® and send a balanced cable (TRS 1/4" or XLR) to the mixer or interface. Not only will this increase the level to what the board is expecting, but it will also balance the line to prevent more noise entering the signal. There could be times where you will need to go from a +4dBu to -10dBV and this box will work with that too since it works in both directions. Either way, the result is a cleaner sound.