A company from the UK has created the Mosquito ultrasonic crowd disruptor that generates a high frequency sound that adults are unable to hear. The sound is not loud enough to be harmful but it is extremely annoying to teenagers. According to this BBC news article the Mosquito works quite well at dispersing large crowds of teenagers:
bbc.co.uk| The Sound that Repels Troublemakers
The baudline ultrasonic analyzer was used to examine the MP3 Mosquito sound file at the end of the article. The spectrogram is below:
Background road noise is visible on the left side of the spectrogram. The right side shows a strong tone that sweeps between 15700 and 16500 Hz. The attack and decay slopes have a typical RC shape. The fact that the Mosquito tone is sweeping probably makes it more effective than a stationary tone would be. The human brain is very good at notching out and ignoring constant tones like NTSC or PAL retrace emissions. A moving tone that looks a lot like a siren demands attention.
Baudline's Play Deck can be used to transform the Mosquito sound into an audible signal for those whose hearing is attenuated above 15kHz. Try slowing the playback down .5X to .25X speed. Or try shifting the signal down about -10000 Hz. The shift slider is equivalent to down mixing which makes it like a radio tuner for audio signals.
An ironic twist has developed, the Mosquito ultrasonic tone is now being used by teenagers as a cell phone ring tone. Most schools require that cell phones be turned off in class rooms and since most teachers can't hear that high in frequency the ringing can go undetected.
What is next in the ever changing Mosquito ultrasonic technological battlefield? Baudline spectrum analyzers in the classroom? It is a possibility. Contact us if you are interested!