[ProAudio] Microphones question

David Josephson dlj at josephson.com
Sat Jun 12 09:54:24 PDT 2021

> On Jun 12, 2021, at 7:42 AM, Dan Lavry via ProAudio <proaudio at bach.pgm.com> wrote:
> Hi again,
> Impedance is one thing, but my question is about circuit generated noise, not impedance. The noise generated by a theoretical resistor is sqrt(4*K*T*R* BW). It is NOT sqrt(4*K*T*Z*BW)  where R is a pure resistor, Z is the impedance. 
Voltage alone doesn’t answer the question, because you need to measure using the weighting network that you use for the circuit noise. It is not only over the BW of interest, but with the weighting of interest. 

Very few manufacturers of mic preamps use a standardized method for reporting equivalent input noise, and even fewer customers are able to compare assertions of different makers. And, manufacturers generally state “typical” figures and will not repair under warranty if a device fails to meet the stated specification. 

David Josephson
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