I have a circuit on veroboard that contains dual supply opamps. I need to send input signal and measure output signal. The input port has a return path we usually call ground and so does the output port. The dual supply input to the circuit has positive supply port, negative supply port and ground terminal since some components in the opamp circuit are connected to be to ground. Note that the opamp circuit is sallen key filter implemented using LM324N.
Do I connect the input signal, output signal and dual supply ground together?
The dual supply is generated using dual bench supply. The middle positive and negative terminal pair from the two internal supplies is connected together to generate ground reference. Below is the picture. Can't upload schematic. 
There seems to be a problem. The output is distorted. The first stage output is below in yellow.
What could cause such distortion in an opamp? The fourth opamp is floating and not used. This type of distortion appears on the input signal of the first stage only after power up and then seems to get worse as seen above.
Best Answer
Yes, ground input and output are the same, and are connected to the center of the PS. To stack two power supplies you have to be sure that they have isolated outputs.
And yes, I would make a good, solid ground connection to connect between them.