Whilst discussing DSP with a good friend of mine, Julio Costa, he reminded me of a terrible sound
that was unleashed on the world nearly 11 years ago.
It's of course the vuvuzela, something so loud, it makes bagpipes sound like gentle whispers.
The bane of every sportscaster and millions of people around the globe.
It became such as nuisance, that several broadcasters developed real time techniques to try and
eliminate or, greatly decrease the drone, with varying degrees of success.
This then, is the perfect sound (or noise - depending on your tastes) to try some DSP on.
Of course it's not real time but still a good exercise.
A quick analysis revealed a very strong fundamental in the low mid range, with harmonics going up
to the 5-7 KHz range, depending on the quality of the recording of course.
A simple notch filter will not be up to the task, those pesky harmonics make sure of that.
Rather what is needed, is a recursive filter, however most traditional "plugin" notch filters, leave a lot
to be desired as regards rejection, ripple, Q and phase changes.
These short comings negatively impact the wanted audio as well, creating a horrible metallic sound.
A bit of head scratching and several Google searches later, revealed a new technique whereby one
can control not only the rejection, but also Q (as the harmonic increases) and phase discontinuities.
At a cost of course, CPU cycles, lots and lots of them.
The idea being:
So what is the result?
First, the original:
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