Originally posted by Azrael
Taking away the frequencies above 4K will lead to a rather muffled sound because it will reduce all the overtones that are responsible for a brilliant sound. I suggest a noisegater and a harmonic exciter instead - and turn of the screen when recording.

According to Celestion's website, only one of their guitar speakers produce sound over 5kHz - 4kHz was, I admit, a low estimate. But adding a harmonic exciter will just increase the fizziness as it piles on yet more high-frequency overtones. You need to be cutting treble, not boosting it.