Once upon a time, John R Pierce pierce@hogranch.com said:
do note, if this is a stage grade electric piano, using big phone plugs, the audio level out is not quite the same as consumer line level that a computer input would want to record, you'll likely have to crank the recording level way up, increasing the noise floor of the recordings. the cure for this is something called a 'DI box'
Line-level is line-level. A keyboard will be putting out an unbalanced line-level signal, and a DI box converts that to a balanced mic-level signal (usually XLR) for a soundboard. Since most computers don't have XLR (or other balanced) input, a DI box is not needed or useful.
Some computers/sound cards only have unbalanced mic-level inputs instead of line-level (and some can be configured for mic or line); if you don't have a line-level input, your best bet is to get something that does (even a basic USB sound "card"), not to amp up the line-level signal to mic-level (especially because most of the mic inputs are mono, not stereo).