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Controlling the lows

greiswig

Power User
I'm still puzzled by the choices I face when controlling bass in this unit, even after 18B. Can someone with enough knowledge (from Fractal, ideally) weigh in and explain the differences between these?

  • "Cut" on the pre tab
  • "XFRMR LF" on the speaker tab
  • "LOW CUT FREQ" on the dyneq tab
  • "LOWCUT FREQ" in the cab block
That last one seems pretty self-explanatory; it's perhaps the last place to control things in the signal string. But in particular, I'm interested in where in the amp's own signal path these various things fall, and what their effect is. Also, are there differences between those parameters in terms of steepness of the cut, etc?

For example, when I built my ODS amp, I ended up learning a lot about how controlling the amount of bass entering the preamp section changed the character of the overdrive in some really positive ways, while still letting you end up hearing enough bass coming out of your speakers. Condensed version is that too much bass in the preamp and you're clipping the bass frequencies too much before you start affecting lower-amplitude frequencies. So if you control it right, you end up with clipping on the mids and highs, and relatively clean bass as a foundation. Which one of the above items should I be focusing on as a way of controlling the bass that is getting into the preamp section? Or should I just spend some more CPU cycles and put a filter block in front of the whole amp?

In contrast, an amp like a Deluxe leans heavily on that extended bass for part of the mojo...so if you want to control the bass, I'm theorizing that it is probably better to control it via that cab block parameter, rather than in the amp block.

Thanks in advance!
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
"Cut" engages a lowshelf filter at the input. This would be analogous to partially bypassing the input buffer cathode on a tube amp.

"XFRMR LF" sets the low frequency -3dB point of the output transformer. Most transformers actually have a very low -3dB point (contrary to internet wisdom) however their full-power -3dB point is significantly higher. The Xfrmr Drive control sets the full-power -3dB point.

"LOW CUT FREQ" sets the -3dB point of a highpass filter at the input to the preamp. The default value is usually due to the coupling cap between the input buffer and first triode stage (but not always).

"LOWCUT FREQ" in the cab block sets sets the -3dB point of a highpass filter at the output of the cab block.
 

greiswig

Power User
Thanks again. So are "Cut" and "Low Cut Freq" part of the same control? IOW, is the Freq parameter the adjustment of the knee for the Cut parameter? That would be what I'm looking for.
 

Hubertus

Power User
Thanks again. So are "Cut" and "Low Cut Freq" part of the same control? IOW, is the Freq parameter the adjustment of the knee for the Cut parameter? That would be what I'm looking for.
According to the Wiki:
Low Cut Freq controls the amount of lows the amp sim sees. It's a blocking filter at the input (before distortion). Ranges from 10-1000Hz, with the lowest setting basically letting all the lows you feed it in. The main practical use for this is to tighten up a tubby bass end. Somewhere between 10-150Hz is generally where it will sound best for standard guitar tones. It's an adjustable version of the Cut switch on the PRE page.
 

greiswig

Power User
According to the Wiki: Low Cut Freq controls the amount of lows the amp sim sees. It's a blocking filter at the input (before distortion). Ranges from 10-1000Hz, with the lowest setting basically letting all the lows you feed it in. The main practical use for this is to tighten up a tubby bass end. Somewhere between 10-150Hz is generally where it will sound best for standard guitar tones. It's an adjustable version of the Cut switch on the PRE page.
Yeah, I was just about to write that my own little test just now showed that they are independent from one another. Thanks for verifying.

I'd still like to understand more about the differences: is one a steeper slope than the other, or does the "Cut" parameter vary by frequency and slope by each amp type, or...?

Sorry, I'm a studio guy: I think in these terms.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
They are unrelated. The cut is a fixed lowshelf filter. Lowcut is an adjustable highpass. For more precise control use any of the myriad EQ resources before the amp block, i.e. a Filter block.
 

clarky

Axe-Master
For more precise control use any of the myriad EQ resources before the amp block, i.e. a Filter block.
if you want a tight low end..
everything you need is right here…

Filter block: Lowcut=700 will normally do the trick..
and if it's still not enough, switch on the Cut switch in the amp block
this will strip a lot of low end tho..
so in the amp:EQ page, a little cut in the 500 band, and a little boost in the bands below will put the newly de-flubbed lows back
 

darrenw5094

Inspired
if you want a tight low end..
everything you need is right here…

Filter block: Lowcut=700 will normally do the trick..
and if it's still not enough, switch on the Cut switch in the amp block
this will strip a lot of low end tho..
so in the amp:EQ page, a little cut in the 500 band, and a little boost in the bands below will put the newly de-flubbed lows back
Any chance of a sample preset with this method. I also need to study the low cut thing. :)
 

greiswig

Power User
if you want a tight low end.. everything you need is right here… Filter block: Lowcut=700 will normally do the trick.. and if it's still not enough, switch on the Cut switch in the amp block this will strip a lot of low end tho.. so in the amp:EQ page, a little cut in the 500 band, and a little boost in the bands below will put the newly de-flubbed lows back
700Hz seems really high! I've been fooling with it today, and it does offer better control in some cases: a low-Q 2nd order high pass filter works well to get rid of some of the subsonic mud that your can get, especially with certain amps. But I'm finding it most useful to set it around 70-90Hz to retain the body of the tone, but not step on the bass line.
 

clarky

Axe-Master
Any chance of a sample preset with this method. I also need to study the low cut thing. :)
sorry matey I don't have any.. this is because I don't really use any amps that require this sort of intervention..

try this very simply experiment

amp -> cab
amp = recto1 orng modern
cab = 4x12 TV mix [a simple bench mark cab for me]

set the amp to screaming hot
high input-drive settings [greater than 6]
turn on the boost switch to so things are really cooking
but use the regular Mesa rule of thumb: do not set the bass control above 3.0 because flub city becomes flub universe [which is harder to dial out]

palm mute and you are now in flub city

amp: basic page - switch on the 'cut' switch
this will improve but not enough

in the grid location before the amp, add a filter block
you now have -> filter -> amp -> cab ->
in the filter block on the 1st page [towards the bottom] you'll see the Lowcut control. set this to 700

you will notice that the flub vanished and you end up with a tight but rather thin sounding low end..
that's ok.. all we are doing is preventing a big chunk of the low end from the guitar from getting into the amp, so the amp's gain can't chew it up..
so what we do is to put the bass back after the amp's preamp has done it's thing

amp: eq page.
all bands at 0dB except the following:
500 = -4
250 = 1
125 = 2
63 = 2

you really don't need me to make a preset for you for something like this..
A - it's very basic stuff
B - you'll get so much more out of this by hearing / experiencing the tonal impact of each little change you make for yourself
 

clarky

Axe-Master
700Hz seems really high! I've been fooling with it today, and it does offer better control in some cases: a low-Q 2nd order high pass filter works well to get rid of some of the subsonic mud that your can get, especially with certain amps. But I'm finding it most useful to set it around 70-90Hz to retain the body of the tone, but not step on the bass line.
I know it seems high.. but seriously, it depends upon the amp you're doing this to..

for my hi-gain tones I'm a 5153Red / Herbert ch3 user..
these guys do not need pre-eq at all
cos they are beautiful just the way they are..
 

greiswig

Power User
One thing I have found helpful in the past is that after I have normalized all my presets for overall volume, I then turn off my studio monitors but leave the subwoofer on. Then go back through the presets and see if there are any that are really woolly coming through the sub, where they will clearly step on the bass player. Seems to help make the soundman's job easier, and to my ear it sits better in the mix without channel processing.

But there are sure a lot of different ways you can cut lows in the AxeFX!
 
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