As previously discussed, the electrochemical noise signal is generated
by an asymmetry of the electrode behavior on a short timescale
(single events) but, on a longer timescale, two electrodes can
be considered to be practically identically noisy if, on average, the
intensity, number and frequency of anodic and cathodic events on
the two electrodes are closely similar.From the viewpoint of the
equivalent circuits (Fig. 2a and b), the two electrodes can be considered
identical if, over a defined timeframe, R1 is close to R2
and the variance of i1 is close to the variance of i2. It is worth noting
that under the usual assumption that R1 = R2, it follows from Eq.
(14) that even a strong asymmetry in the values of i1 and i2 does
not affect the value of the estimated noise resistances. On the other
hand, if R1 – R2, then an asymmetry in the magnitude of the noise
sources might have significant impact on the value of the estimated
noise resistance.In order to partially quantify electrode
asymmetry from the equivalent circuit viewpoint, it is useful to
evaluate the difference between Rn,1 and Rn,2 in the following two
cases; (i) when the magnitude of the noise source on one electrode
largely exceeds the magnitude of the noise source on the other
electrode, but the electrode resistances have comparable values
and (ii) when the resistance of one electrode largely exceeds the
resistance of the other electrode, but the noise sources have comparable
values.In the first case, it is assumed that r2(i1)r2(i2),
and R1 R2 ; therefore