Guitar Audio Frequency
Guitar audio range is
not 400Hz-20kHz:
If you use a Dropped B/Standar B tuning you will go down to 61.74 Hz on 6th string. With Standard E tuning your fundamental frequency on 6th string will be 82.41 Hz.
From experience I have never seen any tuning schemes higher than Standard E. With this scheme, if you have a 24 fret guitar, plucking the 1st string open will give you 329.63 Hz fundamental, on 24th fret(2 octaves higher) the highest fundamental frequency you can achieve is going to be 329.63× 2× 2 = 1318.52 Hz.
Considering that you have Floyd Rose tremolo, without breaking the 1st string you can go maybe 3 octaves higher (I believe this impossible on 24th fret but we are calculating extremes here) giving you a fundamental frequency of 1318.52×2³=10548.16 Hz. This will produce almost no amplitude by the way.
To achieve a natural guitar sound recording you will not need more than the 3rd harmonic of the sound in my opinion.
Standard E tuning:
Fundamental Range(open): 82.41 Hz - 329.63 Hz
3rd Harmonic Range(open): 659.28 Hz - 2637.04 Hz
24th Fundamental Range : 329.64 Hz - 1318.52 Hz
24th Fret Harmonic Range: 2637.12 Hz - 10548.16 Hz
Floyd Rose Screamer : - 80kHz (Inaudible)
Recording Filter Theoretic: 82.41 Hz - 20kHz (Highest Audible)
Recording Filter Practical : 82.41 Hz - 11kHz
Pick-ups will not be able to capture audible amplitude of 2nd/3rd order harmonics on 18-24th frets of the guitar on first string. This is why you will hear "cleaner" sounds on very high notes.
With alternate tuning schemes included down to Standard B your filter should setup should be:
Low-pass @ 11kHz (you might not even need a low-pass for this project imo)
High-pass @ 60Hz
I advise you to use 8th order butterworth filter for the high pass to eliminate 50Hz noise, if you are living in the states make sure to use shielded cables and shield the hell out of your project box to get rid of the 60 Hz noise.
To save space try using switched capacitor low pass filters @ ~8$ a piece from digikey. They are kinda expensive but are worth it.
Conclusion:
Filter Range: 60 Hz - 11kHz
frequency reference