Inductor

Placement

Important spec

There is a limit called $I_{sat}$ ($I$ saturated) $I_{sat}$ is a value of current that a inductor start to act like a normal resistor.

$DCR$ resistant at DC

$ESR$ resistant at measure frequency

Problem with iron core inductor

iron tent to hold residual charge so it will smear the signal this will not critical in low frequency but I will color the sound of higher frequency