audio interface input impedance

Discussion in 'Digital Audio' started by ChrisA, Jan 17, 2009.

  1. ChrisA macrumors G4

    Jan 5, 2006
    Redondo Beach, California
    I'm shopping for an audio interface and now I'm down to reading the specs. I want to record guitar and bass "direct". When I read the specs I notice some of the interfaces have instruments specs at an input impedance of 1 mega ohm. (E-MU is one that is like this) but others are in the 200K to 250K ohm range. Looking at what is inside the typical electric guitar I'm thinking 1M ohm is almont a requirement

    But then on the e-mu unit the line-in impedance is also 1M ohm. This seems way to high for line in. I'd expect it might pick up all kinds of noise and hum.

    It seems that the people who make these interfaces tend to set the line in and guitar inputs to the same thing. So If I go with e-mu I get the good 1M guitar but have to live with a 1M line in. If I got with m-audio I get a reasonable line in impedance but the guitar is at 200K.

    They all seem to get the XLR inputs correct.

    How much does this matter? My guess is not much but I thought I'd ask. Those 1M ohm line-in seems odd.
  2. rtdrury macrumors newbie

    Jul 3, 2009
    no need to match impedances

    Impedance-matching is not beneficial in audio signal chains, although certain impedance ratios can create colorations that people like, usually involving transducers/transformers. Impedance-bridging, which seeks to minimize source impedance and maximize load impedance will enhance the signal/noise ratio and minimize coloration.

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