Analysis of information sources in references of the Wikipedia article "Line level" in English language version.
Practically speaking, electrical engineering transmission line theory does not apply to real world audio lines. ... This paves the way for simple R-C modeling of our audio line.
Outputs are low impedance and must only be connected to high impedance inputs -- never, never tie two outputs directly together -- never. If you do, then each output tries to drive the very low impedance of the other, forcing both outputs into current-limit and possible damage. As a minimum, severe signal loss results.
