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When working with outboard effects, microphones, preamps etc. the impedance may vary and some combinations may have a bad influence on the signal/operation of the equipment.

Consider the following possibilities:

  1. Low -> Low
  2. Low -> High
  3. High -> High
  4. High -> Low

What is the typical audible consequences of mismatches (and which are "mismatches")?

  • @Andyaka - I clarified the question a little - your answers may require an adjustment. Please let me know if I miss some important aspect to this impedance topic.. – Michael Hansen Buur Oct 15 '15 at 12:09
  • @ToddWilcox - see above. – Michael Hansen Buur Oct 15 '15 at 12:10
  • Do you have actual examples of a low impedance driving into a low impedance (and I'm thinking audio equipment rather than antennas and transmitters). – Andy aka Oct 15 '15 at 12:33
  • @Andyaka - we have some vintage preamps at the studio which is at the 1K range. In combination "high" impedance overhead mic (200-400 Ohm) it will definitely not be within the recommended 1:10 ratio. – Michael Hansen Buur Oct 17 '15 at 15:02
  • I found this article which get pretty well around the whole impedance thing - soundonsound.com/sos/jan03/articles/impedanceworkshop.asp – Michael Hansen Buur Oct 17 '15 at 15:05
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It depends a lot on the kind of equipment. Sometimes equipment is designed to have a low impedance output and be connected to a much higher impedance input. Other times equipment is designed so that the output and input impedances are to be matched as closely as possible.

The possible consequences are wide-ranging. Anything from loss of signal strength to overdrive and/or poor low end or high end response. Damage to equipment is also a possible consequence of improper impedance matching at higher power levels.

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Speaking as an electronics engineer, the general rule (below radio frequencies), when designing amplifiers and various audio interfaces is try and make outputs low impedance and inputs high impedance. If you connect a high output impedance to a low input impedance you get signal loss and when restoring that signal loss (with gain) you'll amplify the noise floor and this might be annoying.

So, a low output impedance feeding a high input impedance isn't going to attract any measurable signal loss unless you are doing something stupid like feeding a PA output into a microphone or guitar input. Expect the magic smoke if you do that.

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In 2015, you are very likely to never hear a difference unless you have perfect hearing which is virtually impossible unless you are one of the 96k audiophile fans... (No one else is)

It's the difference between a ride bell in A and A# that is pushed to the back of a metal recording.

You can see it in waveforms though.

As for signal loss - best practice is to always use the shortest and best quality cable possible.

  • Sorry, but that is simply not true. Ever tried connecting a guitar directly to the interface/mixer without a hi-z input? – Michael Hansen Buur Oct 17 '15 at 15:07
  • Yes actually. One of my amps took a crap and I ran it straight to a Tascam DM. Played the set (nearly 2 hours) and the only complaint I had was that I didn't have the amp behind me for a "real" monitor. – F-N-newb Oct 17 '15 at 15:21
  • In recording, I have a chain that I pull up in my DAW and I use it exclusively for recording a SCHECTER direct in to my interface. The voodoo you are talking about is negligible. – F-N-newb Oct 17 '15 at 15:22
  • Now of it is semantics you're after, no one runs things backwards. In consumer electronics there are those buttons... – F-N-newb Oct 17 '15 at 15:26

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