Getting Started with LTspice
LightningHawk 
Simulation: DC Transfer
The DC Transfer function calculates the low frequency gain and the input and output resistances of your circuit. Continuing with the Electret Mic Breakout Board product as our example we can first compute the transfer function. We know that the output voltage is biased at 1/2 the input voltage. Since the Transfer function describes the behavior of the output as a function of the input and we can say the transfer function should be equal to 1/2. If we choose VCC to be 5V then Vout is 2.5V. This circuit should have low output impedance because we want op-amps to operate like ideal voltage sources. This ensures maximum power is delivered at the output giving your ADC the best values. The closer the output impedance is to zero the better. Similarly we want the input impedance to be high as to not draw current from the source. Let's sim the transfer function and verify it has been designed accordingly.