Sometimes data has spikes which are clearly artefacts of the
processing or are due to some other external source. One is used
to seeing these on time series but in some cases there are
unrepresentative “spikes” in the frequency analysed data. An
example spectrum is shown below. There are clearly several
spikes which at first sight could be mistaken for very narrow
band resonant responses. Looking at the spectrum on a dB scale
(or a log scale) shows the expected underlying spectral
structure. This is basically a series of “bumps”. The objective
is to obtain a better visualisation of this underlying
structure. One could acquire more data to reduce the scatter and
indeed this should be done in the present case as there was a
very low number of statistical degrees of freedom. However as is
sometimes the case the opportunity to take more data was not
available and we have to make do with what we have! The
underlying trend is obvious in the graph shown in Figure 2.
However if we just trend the original signal the ‘