Line level is the standard signal strength used with all pro audio equipment.  Which is why mic/instrument level signals are first boosted to line level before entering the signal chain.

Instrument level signals, which come from electric guitar/bass, are sent through a standard guitar cable, which is then boosted to line level using a direct box.

Mic level signals, which come from your mics, are sent though a standard microphone cable, which is then boosted to line level using a mic preamp.

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