Welcome to the Massey University speech project. This part concerns a system to find the (x,y,z) co-ordinate of a moving sound source.
In essence this is a type of Sonar - similar systems are used in the marine industry. The system is passive in that it does no emit any sound waves
but only receives from the acoustic source. The current system uses 5 micophones and computes the co-ordinates based on time-delay estimation
bewteen the source and the microphones. Time-delay estimation is harder than it looks since there are many problems in a real environment such
as additive noise and room reverberation.Reverberation is the acoustic equivalent of multi-path propogation in communication systems. Thus an acoustic wave
may well reach a microphone via more than one path. This can lead to false readings. There is a huge literature on acoustic bearing estimation - too much
for this webpage. If you have labview you can run a simulation of a 4-microphone acoustic bearing estimator where the source moves in a circle.
The present system in the picture link above was built by a final year Mechatronics student for his year 4 project. The system uses a camera
which tracks a radio around the room.Time-delay estimation is done using the PHAT algorithm (phase-transform). There are other similar algorithms
eg the SCOT algorithm,Hanan-Thomson method and so on.All these methods use the so-called Generalized Cross Correlation method which is an extension
of ordinary cross-correlation since the ordinary method works effectivly only when the source is white-noise! The methods only differ in the weightings
that are used within the cross-correlation integral. The method uses the fast-fourier transform (FFT).The accuracy of teh system is down to how
accurate a time-delay you can measure. Delays can only be an integer number of sample instants (normally) so this in itself introduces errors.
The higher the sample rate the more acurate. Here we use a sample rate of 40kHz for each channel.