Via Boing Boing - 'Hooligan chants silenced by delayed echoes', a New Scientist story looking at the work of Dutch researchers who are using out-of-sync replayed sound to disrupt synchronised chanting at football matches.
"Soccer hooligans could be silenced by a new sound system that neutralises chanting with a carefully timed echo. Stadiums could use the technique to defuse abusive or racist chants, say the Dutch researchers behind it. The echoes trip up efforts to synchronise a chant, neutralising an unwelcome message without drowning out the overall roar of a crowd.
Sander van Wijngaarden, who researches human acoustics at the Netherlands Organisation for Applied Scientific Research in Delft, began working on the technique in 2004 after several Dutch soccer matches were blighted by abusive chanting.
"We knew that people become confused if you feed their speech back with a delay," he told New Scientist. "So we wanted to try and apply it in a group context." ... Volunteers were surrounded by loudspeakers that simulated the sound of a chanting crowd and were asked join in. However one speaker replayed the crowd's chant with a short delay.
When the delay was greater than 200 milliseconds the volunteers found it too difficult to chant coherently. Increasing the delay, up to about 1 second, was even more effective. "It was very confusing," van Wijngaarden says."
Yes, this could be used to disrupt racist chanting. It could also be used to disrupt chanting of anything the management (or sponsors) of the match (or state visit, perhaps) don't want to be heard. As 'Kim' points out in a comment at We Make Money Not Art, "it really means that it can disrupt any crowds".
Remember, if aiming to introduce a new control measure, always publicly target it at the most extreme or undesirable behaviour first of all, and you will win more supporters, who will only slowly fall away, conflicted by their beliefs. Isn't that what Martin Niemöller taught us?
Anyway, here's another couple of issues - If a speaker system is used to broadcast back the crowd's chanting (which may be offensive), then:
a) It's illegally publicly re-broadcasting copyright material without the consent of crowd members b) It's illegally publicly broadcasting offensive material