Analysis of information sources in references of the Wikipedia article "Line level" in English language version.
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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.
