### Peter Kootsookos (@kootsoop)

Peter Kootsookos has worked in a mixture of academic research and commercial interests in Australia, Ireland, and the United States. His DSP interests are in estimation, filtering and extraction of information from images and video.

## Deesspee #5

September 16, 20091 comment
Deesspee #5 - Computers

## The Nature of Circles

What do you mean?

When calculating the mean of a list of numbers, the obvious approach is to sum them and divide by how many there are.

Suppose I give you a list of two numbers:

• 0
• 359

What is their mean? The obvious answer is 179.5.

If I told you that the numbers were compass bearings in degrees, what would your answer be then? Does 179.5 seem correct?

In the case of compass bearings, 0 is the same direction as 360. When talking about angles in the DSP world, we often talk about...

## Correlation without pre-whitening is often misleading

White Lies

Correlation, as one of the first tools DSP users add to their tool box, can automate locating a known signal within a second (usually larger) signal. The expected result of a correlation is a nice sharp peak at the location of the known signal and few, if any, extraneous peaks.

A little thought will show this to be incorrect: correlating a signal with itself is only guaranteed to give a sharp peak if the signal's samples are uncorrelated --- for example if the signal is composed...