Riddle me this. What sounds like an elephant when all alone, but sounds like a swarm of bees when numbers grow? The answer, as any World Cup aficionado will tell you, is the vuvuzela. A meter long plastic horn that has become synonymous with the 2011 World Cup in South Africa and has had many fans reaching for the mute button on their TV remote controls. The BBC has received so many complaints it is looking at ways to minimize the noise of the so-called instrument. Now researchers at the Centre for Digital Music (C4DM) at Queen Mary, University of London have come up with a "devuvuzelator" that filters out the droning sounds of vuvuzela for anyone watching the World Cup on a computer.
The sound of vuvuzela drowning out the commentary on television has been one of the main complaints from World Cup viewers. Critics also argue it renders the oohs, aahs and cheers of the crowd that add excitement to the game, inaudible. By analysing the sound of vuvuzela, Dr. Chris Cannam and a team of researchers from the C4DM have devised a devuvuzelator filter which could largely remove the sound of the horns and improve the clarity of the commentary and the crowd noise. The filter is also simple enough to run in real-time, so it can be applied to a live broadcast as it happens.
Various approaches have been discussed by audio engineers, most commonly using "notch filtering", which removes sound energy from specific frequencies. The vuvuzela sound energy is mostly found within narrow frequency bands – the fundamental frequency (approximately 230 Hz) and some higher overtones – so targeting those specific frequencies is a reasonable way to quieten the vuvuzela sound. Unfortunately, notch filtering also has a tendency to remove some of the energy from the commentator's voice too, since the frequency distributions of the voice and vuvuzela overlap.
Dan Stowell of the C4DM said, "Our approach was to make a filter which estimates the amount of energy in the signal contributed by vuvuzelas, at the specific frequencies expected, and then subtracts just that energy. This 'adaptive' approach potentially preserves the voice energy in the signal and helps preserve voice quality."
Anyone who has had enough of the incessant droning of vuvuzela during their World Cup viewing can download the devuvuzelator at isophonics.net.