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High Quality mode

Dave Merrill

Experienced
I'm pretty certain I hear a quite noticable difference in sound when I turn on high quality mode, in the cab block preamp specifically. There's significantly more detail and clarity.

CPU doesn't seem to go up much if at all, so it's a good tradeoff for me.

Anyone else experience anything similar, or check it out and disagree?
 
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unix-guy

Legend!
There are two places I'm aware of where that setting exists: Cab block Preamp and Reverb block.

I can definitely hear a difference in the Preamp. There's a bit of a CPU bump.

I prefer it on in the Reverb block, too... But I would be totally happy with Normal if that was all that existed. I think there's a decent CPU hit for that.
 
I didn't know there was this feature for the cabs until just now when I checked (Economy versus High Quality) but I did notice that the sound quality improved by a noticeable difference as well when I changed it to the high quality mode for a reverb (and the CPU barely increased).

I have not seen this option for anything else yet but I'll have to check around and see what else can be switched to "High Quality" since the improvement was a noticeable one and it barely affected the CPU :)
 

Joe Bfstplk

Power User
Is the amp block oversampling why a 40kHz upper limit on preamp tube frequency response is possible despite a 48k sample rate? I remember a post I read recently that touched on this, and would like to know if I understand 'oversampling' correctly as it is used here....
 

MaVo

Member
I guess there are quite a few very dynamic and nonlinear processes happening wthin a guitar tube amplifier circuit, that require a high sampling rate / low sampling time in order to accurately model the physics happening in the real system. In classic linear control system theory the baseline sampling time orientates on the lowest time constant of the plant which needs to be controlled, e.g. for electrical drives the electrical time constant (determined by the inductance and the resistance of the motor winding: tau = L/R ) is usually in the millisecond range. The classical rule of thumb is to choose a sampling time 1/10 of the minimum time constant of the plant. For highly nonlinear systems like a guitar tube amplifier 1/10 might only be a pretty rough starting point, so that's my guess why the oversampling is so high for the amp block.
 

MaVo

Member
Check out some papers on the International Conference of Digital Audio Effects on the subject of modelling guitat tube amp amplifier circuits. In a few papers certain concepts and patents of Fractal Audio (MIMIC) and Christoph Kemper are mentioned. This one of the few newer sources in terms of mathematical modeling of guitar tube amplifiers.

http://dafx.de/
 

Piing

Power User
I always use the CAB Preamp in High Quality, in all my presets, since it was created at the Axe-FX II. Normally with a Tape, FET or Vintage.

I raise the Drive right before it goes to the red line, and slightly increase the Saturation.

Note that if you do not increase these buttons, the Preamp will have no impact on the sound

From the Wiki:
If PREAMP TYPE is set to anything other than NONE, the preamp is active. But it will have no impact on the sound if DRIVE and SATURATION are both turned fully CCW. Also, PREAMP TYPE affects only DRIVE and SATURATION, not the tone controls.
https://wiki.fractalaudio.com/axefx2/index.php?title=Cab_block
 

lqdsnddist

Axe-Master
I always set to high quality, but, if someone snuck in and changed it to economy, I am 99.9% sure I wouldn’t notice
 

Tommy Tempest

Power User
I think it's noticeable enough to set it to high quality. Kind of like the filters settings in the preamp section of the cab block. I notice an improvement when switching them to 24dB/Oct. It seems the bottom is tighter and there is more clarity.
 
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