I want to buy an Audio Interface and Condenser Microphone to record to my PC. I found the two following matching my needs:

But according to several Audio-related sources like e.g. mynewmicrophone.com the Load-Impedance of the Audio Interface should be at least five times higher than the Output Impedance of the Microphone.

SSL 12 Specs say it's mic input has an impedance of 1.2 kΩ and the homepage of the OC818 states that it has an impedance of 275 Ω. This would be a ratio of only ~4.36. This is less than the often recommended 10 or even 5. How bad would that be?

The Specs of the OC818 also state that only Load impedance of "> 1 kΩ" is required - which would be met in our case - but how much would be the influence of being under the generally recommended limit of having at least five times the impedance?

1 Answer 1


Some manufacturers, such as Neumann, recommend the load impedance of the audio interface to be at least 5 times higher than the output impedance of the microphone, which is the minimum load impedance at which the manufacturer guarantees all specs in order to deliver its full frequency response.

Using AEA Ribbon mics the ratio is from 4 to 5 times, meaning if the mic has an output impedance of 300 ohms, the preamp should have at least an input impedance of 1200 to 1500 ohms.

Other manufacturers such as PreSonus recommend a mic of half the impedance of the interface input for optimal results.

Low microphone output impedance usually allow for very long cable runs without sound degradation.

Hence usually the exact value will matter to those who often have to work with very long cable runs.

In your case I don't think it would make much of a difference in a home studio setup where the cable runs are short, and generally you are within the recommended ratio.

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