When watching the soccer World Cup, you will hear a constant horn sound. The problem is that it has a tendency to drown out the noise of the TV announcers. Here are some tutorials on how to get rid of the noise while watching.
The way it works is by using an application that detects the fundamental frequency of the horns, which is around 233Hz and apply a notch filter to it.
You can download it from the National Instruments blog post [here].