i'll paraphrase ericgibbs' pm here so ppl like me have an idea:
ericgibbs:
"R2/R3 divide the +V1 into half [the centre point of the +V supply] By applying this Vss/2 to the TL opa NI inputs , this sets the operating point of the opa's OUTPUTS to V1/2. This means without an audio signal the opa outputs sit at +2.5V, so any audio signal will drive the opa down towards 0V and up towards +V1.. This means the signal will be symetrical about +2.5V,,, this is what you want in a 'ac' amplifier, when its only got a single power supply line [+5v].
The C4 is just noise decoupling of this centre point voltage.
C5 will act as a filter with with R9/10. The LM393 comparator has positive feedback R12, so R9/10 C5 and R12 work together to determine at which voltage point on the audio signal, the signal is squared up by the LM393.
"
This clears a lot of stuff up for me; except one
. If anyone could explain how the comparator and that part of the circuit works? with a little equations incorporated if possible.
your input is greatly appreciated,
(i feel like an information leech, i haven't been able to really help anyone yet. but it'll happen as soon as i get this project done, I'm going to post a huge tutorial on automated guitar tuning with servos)