[sdiy] Single supply opamp as inverting summing amplifier

[Seb Francis]

An analog question in a digital age ... ;)

I'm designing the front end for an audio CODEC.  I'd like the whole 
thing to run off a 5V supply (well 2x 5V supplies really - 1 digital, 1 
analog), so I'm using AD823 opamps which are pretty good for audio and 
can swing very near both the positive and negative supply rails.

So, I have an AD823 wired as an inverting summing amplifier to sum the 
different inputs together.  The + input then needs to be at 2.5V.  So 
should I just make a potential divider between 5V and 0V?  This seems 
like it might introduce noise from the power rail.  Is there a standard 
trick used in this kind of situation to get the signal to float between 
V+ and 0V?

TIA,
Seb