Loosing hi-freq information

I’m doing a home recording test: a simple condenser mic placement comparison in front of my Fender Deluxe Reverb amp. I’m using an old Scarlett 2i2 and nothing else. The Supervision plugin on the input channel shows me that I’m losing information > 5 kHz, and this seems the most important degradation factor. The project is in 48kHz and 24 bit. I can imagine that with and hi-end interface (RME Fireface UFX+ is on my wishlist) the AD conversion would be much better. I also understand that low amp volume means more pre gain and so more noise floor.
Am I missing something? Maybe some Cubase plugin?

Saying that, is it normal to lose so much information in high frequencies? My amp really covers the full spectrum. Even turning treble all the way up, the amp tone is mostly gone.
So I’m considering buying a Kemper and simplifying the process (a good interface is required anyway, I know). Would you use some plugins? I’d like to obtain a pro-level amp sound, so I could buy an RME interface and maybe a WA-273-EQ to control the signal even before the AD conversion.
I just want to be sure it’s worth the money.

Most guitar speakers don’t go higher than 6 kHz.
Are you really sure you have a full spectrum speaker ?

It’s not an FRFR, but I can clearly hear a large part of the tone completely disappear during the process. This Fender amp has huge highs. If under 6kHz, anyway, the 5-6 kHz range could be the problem, am I right? Have you ever experienced this kind of problem?

I would suspect the mic first and then the interface.
Definitely not a Cubase issue…

Is it doing a steep cutoff at 5 kHz and you have really no peak after that ?
Just put your mic in front of your monitoring speakers and play a song just to be sure.

Also you amp uses a Jensen C12K speaker that has this response at 8 Ohm :

Exactly! Over 5 kHz my response is so low that the highs part of the graph is totally missing. I’ve noticed that poor cables or poor conversion, in general, affect high freqs firstly. Maybe I should just try with better hardware. I’m new to the home recording so it could be the overall quality that scares me. Maybe it’s a matter of signal quality in general. I’ll do some other tests with a little more volume on the amp and less gain on the preamp, and I’ll give you more graphical information. I was looking for the “sweet spot”, which sounds like “the tone I hear while playing” to me. My amp sounds really “brilliant” and it’s frustrating to lose all this even tweaking with the amp eq.

Okay, got it !
I understand what you say but low quality cables or converters will never cut the highs like that. It can attenuate it a bit, but doesn’t make cuts like a low-pass filter would do.

Forget the amp, the problem either comes from the mic or the interface, but most probably the mic.
If you have a keyboard or anything else you can plug into your interface, see if there is any issue.
If there isn’t, then it’s the mic. Try recording your voice to confirm. Your mic may also have a filter switch ?

To be honnest concerning the hardware, there won’t be that much difference between a Focusrite interface and a high-end RME. Better converters may lead to slightly better quality in the highs, but in a full mix you will never be able to tell the difference, plus you will probably add EQ, compression, etc to adjust your recording. Nothing to worry about.

The most important things in guitar recording are the microphone (the main thing that will affect your tone) and the cable length (as long as you use good cables like Cordial CGK 175, don’t go higher than 10 m for your total chain, including pedalboard, but still, the shorter the better)

A simple test would be to try recording a different source, for example your voice or an acoustic guitar and see if the problem still happens. Then try a DI source, like your electric guitar. If the problem occurs only with the mic, that would indicate the mic is the problem!
As @Louis_R suggests, you are unlikely to notice differences in DA/AD conversion unless you have high end monitoring and a well treated room.

Finally, the problem was the volume! I’ve done a test doubling the volume and the mic is getting the source much better. Thank you all!

I’m glad you found a solution ! But still it does not explain why the mic is cutting at 5 kHz when the sound pressure level isn’t high enough.

Maybe the high preamp level was affecting the tone, or more probably the mic couldn’t receive enough signal: the main difference between being in the amp room or in the control room to me is the “airy fullness” of the real sound and a noticeable cut of the high-frequency harmonics.