Circuitry for Digital Multi-Effect Guitar Pedal using Daisy Seed

Guitar Pedals
1

Hello, sorry if this is a dumb question.
I’m trying to design the circuitry required to build a guitar pedal using the daisy seed to run the software we’ll write to complete DSP operations, but I’m having trouble trying to understand what other people have done in the past.
The Daisy Seed datasheet says that the absolute min/max voltage of the Audio_In pin is -1.8V/1.8V (3.6Vpp), however I’ve seen schematics of input circuitry that add voltage to the input of the op amp such as this:

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My question is why there is an audiobias/increase in voltage into the input circuit? I don’t see why we wouldn’t just try to achieve line level.
Any guidance on tis would be appreciated, thanks!

2

I’m still learning so someone please correct me if I’m wrong.

The op amps receive only a single power supply (5v and ground) so without the 2.5v bias, the output signal would be offset and not centered around 0.

What I don’t understand is why is R38 present? Doesn’t this reduce the 2.5v? The way R33 and R35 are arranged on the OP1654 makes more sense. Why have two different arrangements been used? And for that matter why have different op amps for input and output been used? They were the same on the Field I believe?