I have a bunch of guitar pedals (stompboxes) that are sitting idle. I'd like to run a mono track of music from my computer through these pedals and record it back into the computer again. The audio might be anything from drums to a synth. Of course I'd like the quality of the audio to be as high as possible.

I have a Presonus Firebox which I believe I could use to do this. Here are its specs:


My understanding is that the preamp instrument inputs will be suitable but that I could use a DI box and input to the mic inputs instead? Is this correct? What will the difference in quality be do you think?

What about the line inputs? Can I connect these directly to the pedal chain or is the output impedance too high?


The outputs from the firebox are balanced TRS and have a 51 Ohm output impedance.

  • 2
    In my experience this type of question is best solved by experiment - try all of the options you mentioned and see which you prefer. (Obviously start with minimal input gain to avoid damage, then gradually increase to taste.)
    – Robert
    Commented Jun 27, 2013 at 14:19

1 Answer 1


Since your interface has an instrument input and the stomp boxes are designed to work with an instrument line, I would hazard that the best quality results will likely result from going in to the instrument input. The trick will be to get the output from the audio interface down to the correct impedance for the pedals which may require a significant amount of pad.

  • Thanks for your answer! How might I get the correct impedance at the output? I'm presuming I need some class of attenuator.
    – user4286
    Commented Jun 27, 2013 at 20:04
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    Sorry if it wasn't clear. When I said it needs a significant amount of pad, a pad is the actual device. It reduces the signal strength effectively altering impedance. Alternately, you can use a transformer for slightly higher cost, but possibly better overall result. I'd guess you'd need somewhere around a 40dB pad.
    – AJ Henderson
    Commented Jun 27, 2013 at 20:29
  • Thanks again! Do you mind offering me a few product suggestions which I can look further into. When I search after 40db pad or transformers I seems to always get xlr devices. I need to trs to trs.
    – user4286
    Commented Jun 27, 2013 at 20:43
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    Looking through B&H's selection of pads, this one seems like it would probably work. bhphotovideo.com/c/product/441842-REG/…
    – AJ Henderson
    Commented Jun 27, 2013 at 21:42
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    But it might work just fine without any pad. Of course the interface's output has a ridiculously lower impedance than the stompboxes' guitar input, but that's not in principle a problem in the LF regime.
    – leftaroundabout
    Commented Jul 2, 2013 at 20:18

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