I’m trying to record an electric guitar, specifically an ESP LTD EC1000 Deluxe with Seymour Duncan mics, by connecting it to the instrument (HiZ) input of my Focusrite 18i20 interface. The guitar and cable work fine when connected to an amp, and all the inputs of the interface work fine when mics are connected to them (and recorded into Cubase 9).
But, when I try to record guitar, the resulting sound is lacking all high end and harmonics, as seen in the attached spectrogram, the recording is periodically completely silent above 10khz. Understandably, the sound is very muddy and not at all pleasant. I tried a different guitar, a Jackson King V, and using that I get sound across the full frequency spectrum, but then I instead get overdrive distortion from the first moment on, playing clean is impossible even though there’s no identifiable peaking or clipping throughout the signal chain.
Neither of these artefacts are present when plugging either one of the guitars into an amp, or plugging mics into the same interface inputs.
Does anyone have any idea what might be going on?