Lele
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In the new 3.80 Helix Firmware the Xtra Blue is a very interesting new amp sim and I think I could use it for everything, but it's rather complex for me. So I tried to analyse it more deeply. Maybe the info I put together could help you too. I'll be happy to learn about any mistake or additional information, in case! I never tried the real Bogner XTC amp (but I love the Helix Shiva).
Class: AB vs A
Harmonic structure of tone is very similar, but class A has higher level of higher order harmonics (= a little more brightness) in the pentode mode
Class AB with triode mode offer a little more even harmonics, but it's just +1dB
Triode vs pentode
Triode = a little midrange emphasis, little roll off higher frequencies because of lower level of higher order harmonics (Miller effect), but it's very small; more sensitive to ghost-noting than pentode mode specially if ripple is above 0
Boost low/high
Apart from the obvious much lower gain with "boost low", the "low boost" light saturation is made only of odd harmonics (that often we perceive as little more clarity, but less warm sound)
Structure: it's the gain level of preamp (low or high). "High" means more saturation, more higher order harmonics (=more brightness), but "low" offer a little more first order even harmonics
Bright: off (no capacitor at the input), B1 (similar to Fender Twin bright switch), B2 is an even brighter pre eq. Basically it's a low cut effect depending on the drive level (higher driver, less brightness effect) similar to the treble bleed of the guitar volume knob (when you have that kind of circuit on board)
Depth (or "Excursion" on the real amp): it boosts the lows at about 100 Hz (affecting just a little more than one octave), +3dB (medium), +6dB (loose)
Presence: it gently enhances the highs specially with setting above 5 (between 0 and 5 the effect is very small) starting basically from 1kHz but with more effect from 2 kHz and beyond
Bass: it affects the lows, specially by cutting more near 0 than boosting near 10; the cut is almost like a gentle slope low cut starting at 500Hz; the boost (from 5 to 10) is smaller and starts about at 200 Hz
Mid: this knob has a very weird behaviour; from 5 till 10 there is little change apart from a little wide boost at about 2kHz, but when you adjust it near 0, you get a big boost at about 100Hz or a gentle high cut starting at about 300 Hz. It's a very unexpected result. It's clear this is a crucial tone control in the Bogner 101B amp sim. And maybe if we are used to try "middle" positions (instead of extreme adjustments) we could be disappointed with the result without finding a proper balance with the other tone controls. I'd suggest to start with a high value of mid tone control.
Treble: this is a much more typical tone control affecting gently and widely the highs, centred at about 3-4kHz
Class: AB vs A
Harmonic structure of tone is very similar, but class A has higher level of higher order harmonics (= a little more brightness) in the pentode mode
Class AB with triode mode offer a little more even harmonics, but it's just +1dB
Triode vs pentode
Triode = a little midrange emphasis, little roll off higher frequencies because of lower level of higher order harmonics (Miller effect), but it's very small; more sensitive to ghost-noting than pentode mode specially if ripple is above 0
Boost low/high
Apart from the obvious much lower gain with "boost low", the "low boost" light saturation is made only of odd harmonics (that often we perceive as little more clarity, but less warm sound)
Structure: it's the gain level of preamp (low or high). "High" means more saturation, more higher order harmonics (=more brightness), but "low" offer a little more first order even harmonics
Bright: off (no capacitor at the input), B1 (similar to Fender Twin bright switch), B2 is an even brighter pre eq. Basically it's a low cut effect depending on the drive level (higher driver, less brightness effect) similar to the treble bleed of the guitar volume knob (when you have that kind of circuit on board)
Depth (or "Excursion" on the real amp): it boosts the lows at about 100 Hz (affecting just a little more than one octave), +3dB (medium), +6dB (loose)
Presence: it gently enhances the highs specially with setting above 5 (between 0 and 5 the effect is very small) starting basically from 1kHz but with more effect from 2 kHz and beyond
Bass: it affects the lows, specially by cutting more near 0 than boosting near 10; the cut is almost like a gentle slope low cut starting at 500Hz; the boost (from 5 to 10) is smaller and starts about at 200 Hz
Mid: this knob has a very weird behaviour; from 5 till 10 there is little change apart from a little wide boost at about 2kHz, but when you adjust it near 0, you get a big boost at about 100Hz or a gentle high cut starting at about 300 Hz. It's a very unexpected result. It's clear this is a crucial tone control in the Bogner 101B amp sim. And maybe if we are used to try "middle" positions (instead of extreme adjustments) we could be disappointed with the result without finding a proper balance with the other tone controls. I'd suggest to start with a high value of mid tone control.
Treble: this is a much more typical tone control affecting gently and widely the highs, centred at about 3-4kHz
