Calculates the root mean square Thermal Noise Voltage V_{nrms} in a given bandwidth at a specific temperature that is passively generated across the resistive part 'R' of a circuit element ~ There may be additional "excess noise" generated by current flowing through the resistance due to the type of material and its purity hence the "extra" pink noise from old carbon resistors or shot noise in active devices


Boltzmann constant — k

1.3806x10^{23}

^{ }J/K 
Temperature — T


°C 
High Pass Response –3dB — f_{l}


Hz — Can be zero for d.c. coupled 
Low Pass Response –3dB — f_{h}


Hz — Every circuit has a low pass 
f_{l} and f_{h} Filter order — m


assumed Butterworth response 
Resistance — R


Ω 
Calculated results using the values entered above


Noise Bandwidth — B_{n}



Noise Voltage — V_{nrms}


nV = √4kTB_{n}R 
Noise Level — ref. 1V


dBV = 20 log V_{nrms}/1V 
Noise Level — ref. 0.775V


dB(0.775) or dBu = 20 log V_{nrms}/0.775V 
Noise Level — ref. 1mW in 50Ω


dBm = 10 log (V_{nrms})^{2}/50 x10^{3} 
Reference voltage for calculating Signal/Noise ratio SNR etc.


ReferenceVoltage V


dBr = 20 log (V_{nrms})/Vref 
The noise bandwidth is not the same as a 3dB bandwith and It is possible to enter f_{l} higher than f_{h} as can be done in practice using real cascaded and buffered filters but the math may not always work as expected like when f_{l} = f_{h} ~ The default values are for the Tektronix AA501 audio analyser or similar equipment with an IEC 22.4kHz audio filter with 3rd order Butterworth response For more information about noise in components and amplifiers see: The Art of Electronics 3rd edition chapter 8 ~ By Paul Horowitz and Winfield Hill ~ fellow cynics 
"Do you work it out one by one ~ Or played in combination"