by Prof Allen
(edited by Sarah Robinson, Jan 13, 2017)

show_data.m: Plots stimuli, response data, and impedance (impedance plot depends on a specific configuration of the circuit)
fast.m: Computes Fourier transform
fsst.m: Computes inverse Fourier transform
fig.m: Similar to Matlab's function figure.m, but generates figures in random positions on the screen so they are easy to sort through

Impedance computations:

Make sure to change the value of Rref in the code!!!!!

The code assumes that the unknown impedance (e.g. loudspeaker) is in series 
with a resistor Rref (this value is set in show_data.m). 

One channel is connected to the top of the load, and one to the bottom of the unknown load impedance, 
which in turn is connected to Rref = 1k Ohm. 

For this to work well, one needs to buffer the voltages with an opamp, to remove the leakage currents. 
A good choice is one with a very high input impedance (1GOhm) (Jfet input op-amp).

Then the load impedance is given by (Vx-Vref)/Iref where Iref=Vref/Rref.

Thus: Zx = Rref * (Vx/Vref -1 )