Questions about the old circuit

[Big Mountain]

Hey,
Could someone please tell me things about the old analog signal input conditioner (on the section obsoleted).
I want to know accurately what the circuit does to the incoming signal. The signal from the piezo goes into the analog circuit, then what happens to the signal in there? Is it amplified? And what else? It's said in the text that lm324 converts the signal.
And I would like to know what comes out of the analog circuits output? What kind of a signal goes to the micro control module? And yes, these questions consider the old schematic.
Thanks.