I want to make a device, which takes an AC audio signal like a guitar pickup signal, or piano or what have you as input, and changes the pitch using this function:

```
newFrequency = oldFrequency * 2 ^ ( ( interval - 1 ) / 12 )

```

oldFrequency is the frequency of current note. Interval is just the number of half-steps from that music note, including that note.
For example:
A note at 110Hz with interval = 13 would be A at 220Hz.
A note at 110Hz with interval = 1 would be A at 110Hz.
A note at 110Hz with interval = 7 would be E at 164.814Hz.

That's the case for any music note. Not only A. By the way, interval CAN take negative number for a lower pitch.

The problem is that we have an audio signal at input. One can play multiple notes or a chord at once. Is that going to be a problem?

I'm new to digital electronics, or electronics at all. I would appreciate if you could just give me keywords and leads, so that I could search, study and do more research. I don't know where to begin at all.

Thanks in advance.