My son loves dirt track racing (stay with me here) but the local track is under fire for noise control.  This probably wouldn't work but if you recorded the various cars, A-mods, B-mods etc.  Took them into Sonar and reversed phase and then played that back at the track at fairly high volume over a PA would it actually cancel out some of the noise and lessen the volume?
 
Probably a silly question and not a normal use for recording software.
 
Thanks,
Terry
 
 
 
 

I'm pretty sure this wouldn't work as the sound of the vehicles will be constantly changing in pitch etc., so there wouldn't be any nulling.

I think it's a good idea, BUT it would never work, for exactly the reasons noted in the above reply from the other poster.
 
Flipping the phase only works on identical frequencies.
 
I think you would end up with the noise folks coming a lot sooner and madder.
 
Sorry, 
 
Bob Bone
 

Plant those evergreen bushes that grow tall around the track. Trees as well. That's your best bet but it takes a while.

You are quite clever to think of this, but I agree that there are too many variables.  If you could come up with an advanced technique that worked, you could probably retire to the South of France.
 
I even tried the old trick of recording a second track with no music but only the unwanted hiss and buzz, and reversing phase.  I got only about a 30% (subjective measurement) improvement because of subtle variations, although that plus HPF helped.
 
The technique is best for very constant sounds like 60-cycle hum.

Not a silly question at all. That principle is used in active "bass traps" to cancel resonances and flatten room response. Just not very well, and for the same reason the scheme wouldn't work at the race track.
 
The problem is that noise is spreading out and bouncing around in a chaotic fashion, so that the actual spectral characteristics will not measure the same at any two points. Consequently, any correction that worked at one location would not be appropriate for another location.

Love this question. It would be a scientific achievement indeed to do this and I am sure it would cost millions if it were actually possible. Free ear muffs for moaning locals would be much simpler. Or electric cars ;-)

For what it's worth ..I was sharing this post with my son in law, Andy...he thought if you could put a wireless mic on each racer and send that thru reverse polarity unit broadcast thru the PA..interesting thought and perhaps the most feasible!
 

For the sound to "null"... it has to be exactly 180 degrees out of phase.
You wouldn't be able to mic each car... and shoot all that sound thru a PA... and expect it to null.
The cars are moving, the noise is changing dynamically...
The PA would be stationary.
 
Theoretically, If you could mic each car... and each car had an onboard sound generator that could output the same dynamic noise 180 degrees out of phase... this would be plausible.
 
I believe auto manufacturers have already experimented with this for reducing noise
 
 
 

Noise cancellation is a good idea, but not practical w/ so many variables as others have said.  You would have to have a mic at every house and enough computer power to instantly compute the noise and reverse the phase and pa it at that location.  Much like the Bose noise cancelling headphones etc.  Maybe talk to the NSA?
 
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