Pitch Shifter Blending question

[RaceDriver205]

Just working on a DSP pitch shifter, and I want the shifted output to be mixed with the non-shifted signal.
In addition to that, I would like to use a 100K pot for 'blending' the two signals, allowing my expression pedal to be used.
I arrived at this, which I believe will cut one of the signals completely at either pot extreme:

Non-shifted signal is the bottom line, shifted signal the top line. As the input is boosted by 2 (gain), the ouput must be cut by 2.
Does this look OK? (not sure what value for R to use).
Thanks all.

[gez]

There's an article over at Geofex on this very circuit.  I think it's called 'panning for fun', but I might be confusing that with another.  Anyway, it's there somewhere.

[gez]

PS  I breadboarded it once and it worked beautifully.

[RaceDriver205]

Cheers Gez. Ive set R to be 150K, and the feedback resistor to 270K. Should blend correctly and give a gain of 0.5.
Might increase gain a tad after I build it, so it can give greater volume than the input.
Just waiting for the 514256 and the ATTiny26 so I can get this thing going.