Ok, I'm about to show why I'm a digital guy, not an analog guy....

I need to process an audio input before it runs into a modem chip.  I've
designed an active high pass filter using a Microchip MPC6022 dual op amp
which I happened to have lying around.  The filter works fine, but I need
to introduce a DC bias, since without it, the filter cuts off the negative
half of the incoming audio wave.   I used a wheatstone bridge for doing
this (as explained in a Dallas Semiconductor ap note) and it works fine
too, adding about 2.5 volts DC to the incoming audio so the entire signal
is a positive voltage.  The problem is that the first component in the
active filter is a capacitor, which, of course, removes the DC
bias.   There must be some common way of handling this problem and I'm just
too inexperienced with analog circuits to know what it is.  Can someone
point me in the right direction?

Thanks,

John Hansen

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