Wednesday, August 10, 2005

Using 5.1 Audio and a Microphone as a Tracking Device

Ok, this is just a thought and may be completely unfeasible but I was trying to think the other night how to create a tracking device using regular objects that are low cost and in common use.

I was reading up on how GPS works by sending radio signals from satellites that are sync'd with atomic clocks and then calculating the distance from each satellite by working out how long the signal took to get from the satellite to the receiver thereby allowing the signal to be triangulated. This is an over-simplified view I'm sure, but bear with me.

So, my next thought was... why can't something like this be done for a local setup. Obviously radio waves would travel far too quickly so something slower would be needed, so my first thought was sound.

What if a 5.1 system sent regular high frequency blips from each of it's speakers (each speaker a slightly different frequency) and you used a microphone as a tracker and had software to calculate the relative distance between each of the speakers based on the order and timing of the frequencies on the sampled signal?

I am not a physics or math expert, but I have tried some lamens calculations here. The Soundblaster Audigy can sample at a rate of 96khz. Sounds travels in air at approximately 345 meters per second. Therefore to travel one meter it takes 0.00289 seconds. If 96khz means 96000 samples per second, then that gives a sample every 0.0000104166 seconds. That means a potential 277 samples per meter which could give an accuracy of 0.00361 meters (or 0.3cm). Sounds good. Obviously this is assuming the software could process the signal in realtime. I am assuming some type of Fourier Transform would be needed to split the frequencies back out. I am not sure how quickly that can be done.

Can anyone who knows more about physics than me possibly comment?