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This is sort of a follow-up on this question: How important is impedance matching in audio applications?

So if impedance matching is not important, why don't we use say 1M inputs for line level inputs?

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Xaser
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    A 1M ohm input acts like an antenna and picks up lots of noise.. a low impedance input won't pick up much of anything. So it means unconnected inputs won't swap real signals.... the worst source is mains 50/60 hz hum.. – Spoon Aug 21 '16 at 14:37

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1st. Then you can't get a coax with such characteristics impedance, so no perfect impedance match is possible
2nd. More practical reason: With impedance of 1M you would get all the environment noise, garbagge, etc...A high impedance input is like a pickup for any small signal.

Marko Buršič
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  • Hi, n2 makes perfect sense, but I'm not sure I get what you are trying to say in n1, can you please elaborate or rephrase? (sorry non native speaker) – Xaser Aug 21 '16 at 14:57
  • Forget the n1. The characteristics impedance of the transmission line (cable) matters at high frequency, like RF, it is makes no difference at all if you use different cable (it doesn'e even exist a 600 ohm cable) at audio frequencies – Marko Buršič Aug 21 '16 at 16:01