6-2
exact cutoff frequency depends on both the electrochemical and smoothing
techniques).
There are 3 methods for digital smoothing. These are:
a) a modified variable point linear smoothing routine (Moving Average)
b) a variable point least squares smoothing routine (Least Square)
c) a Fourier Convolution smoothing routine (Fourier Transform)
Moving Average
In the modified 5-point linear smooth, data is examined in 5 point blocks. Within
each block, the first, second, fourth and fifth points are summed and divided by 4.
This number (an averaged current value) replaces the third point in the block. The
averaging routine moves up 1 point, and repeats the averaging sequence. This
routine is repeated for all points.
The first 2 points of the data set are set equal to point 3 and the last 2 points of the
data set are set equal to the third from last point. At times, this appears as
spurious data points at the ends of the plot. This is unavoidable and is normal.
The only requirement for the number of points is a block is that this number is
odd. Any odd number between 5 and 25 can be chosen on the BAS 100W - the
larger the number of points, the greater the smoothing.
Least Squares
This digital smoothing function is based on the work of Savitzky and Golay: A.
Savitzky and M. J. E. Golay, Anal. Chem. 36 (1964) 1627 - 1639. The smoothing
is a quadratic least squares operation working on data blocks of n points (where n
is any odd number between 5 and 25).
Fourier Transform
This digital smoothing routine is based on Prof. Donald Smith's work. A more in-
depth review of this process is given in D. E. Smith, Anal. Chem. 48 (1976) 517A
- 526A and references therein.
The process involves the Fourier Transform of the time or potential based data
array, multiplying this frequency spectrum by a frequency domain filter function
and then performing the inverse Fourier Transform to give filtered original data.
This technique is extremely effective at removing unwanted noise, although the
computation time required is slightly longer than the other smoothing routines.
Data blocks must be less than 1024 points.
The dialog box for Smooth is shown below (Figure 6-2).
