Help me understand cuts in amp block vs cab

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Dirty145

Inspired
I’m trying to understand the difference in making high/low cuts in the amp block (preamp) section versus the cab block (two options here, preamp section and directly on the IR page).

I’m finding that I prefer the tone when I make the cuts in the amp block preamp section, however the cuts are VERY drastic (up to 450hz on the low cut). I leave the cab block wide open with no cuts at all. If I made the same cut in the cab block, the difference is much larger with a much bigger sounding cut to the bottom end. Can someone explain the difference and which spot is more preferable to make cuts for tone shaping? Thanks!
 
The EQs operate in a different way. The cab block low and high cut set basically the cutoff frequency and the slope parameter sets how steeply the low or high end rolls off from the set frequency. So for example a low cut at 100 Hz with a 6 dB / octave slope would be less drastic than 12 dB / octave so the low frequencies would be affected less.

The amp block instead uses more surgical cuts, offering you input (before the amp) and output (after the amp) processing. You could achieve the same by adding a graphic EQ block before and after the amp, having them in the amp block is just a convenience feature.

With input EQ the most typical use is what people use overdrive pedals for: boost midrange and cut low end. Cutting low end keeps things tighter and boosting mids makes it all more present. The output EQ is often used to correct for things the amp does. For example if you feel that your amp is a bit too thin sounding you could add some low mids with the output EQ.

There's no right way to do it but most will just use the cab block cuts because they are so straightforward.

If you find you need to cut low end drastically, investigate your output system. You may have headphones, studio monitors, FRFR speakers etc that emphasise low end excessively or maybe the placement is such that it emphasis the lows in the room. The room itself can have an effect on this, e.g. my room at home has a big bump at 130 Hz that I counter with the global EQ.
 
The above explanation is very good, but in case it helps, here are my experiences, mostly based on Mesa Boogie amps I have had, and then seeing the Fractal Models react the same.

To me, I think of it like this:
Different amplifiers react differently to input signals. For example a dual rectifier when sent a full input signal with no cuts can sound flubby, loose, and undefined in the low end. sometimes this is desired for slower massive chords. Other times it is not desired, so a lot of people put a boost like a tube screamer in front, the big thing about the tube screamer is it cuts a lot of lows and boosts a lot of mids, and the amp reacts differently to this. It tends to be much tighter in the low end and allows more articulate playing to come through. The Pre EQ in the amp block can cut those lows to have a similar effect without the additional coloring of a tube screamer or other overdrive. It can also carve out irritating frequencies that your guitar produces. Depending on how strong a signal is in the low/mids/highs, it will hit the "tubes" and distort differently.

The post EQ in the amp block can shape the tone after the preamp. this is really popular in the Mesa Mark series amps with the graphic EQ. Many times you will basically cut the bass by turning the bass knob to 0 on the amp, because it causes the amp to lose its articulation. Then you can boost it after the preamp with the post EQ/Graphic EQ in the amp block. You can have a big, full sound that is still tight because you cut the unwanted frequencies that cause all that flub and muddiness, and boosted the bass after the preamp section (the typical V shape is often used, but not always the best answer so use your ears!)

The cab block has low and high cuts, and I find this handy so you can get rid of subharmonics and things like that the can make the mix sound muddy. its often helpful to cut around 70-120Hz here to clean up the sound more. You can also cut the high end off to get rid of some fizzyness, most guitar loudspeakers don't produce much meaningful sound above 7kHz, and I have found it pretty good to cut the highs at 9-12kHz in the cab block. But as always, use your ears! If you were playing live with a sound engineer mixing, he would likely cut the guitar signal similarly to this, get rid of the lows to make room for the kick drum and bass guitar, and get rid of the highs to let the cymbals shine up there.
 
I too was wondering about this and appreciate the great explanations...very helpful as a newbie. Thanks guys!
 
Yes, great info. What I’m still trying to understand is why I have to make such a drastic cut in the amp block to get the desired results, although they sound better to me. For example, I’m using YA IRs (one cab is a Marshall M25 and the other a Bogner). I’m using the Friedman BE V2 model and I have zero cuts in the cab block (both IR and preamp). I went into the amp block input eq and have a low cut at 450hz and high cut around 7000khz. I engaged the fat control switch and there is still plenty of bottom end and I’m really digging it through the QSC 12.2. Making similar cuts post would result in a very thin sound. Is it normal to make a low cut of 450hz for pre-eq? For reference, I’m using a 60th anniversary 1960 Les Paul reissue with custombuckers.
 
Dirty145 said:
Yes, great info. What I’m still trying to understand is why I have to make such a drastic cut in the amp block to get the desired results,
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Well, you got me curious. Check out this vid as it may apply. Basically he's saying that pre- or post-amp EQ is affected more significantly depending on the source of gain. You don't have to watch but the first couple of minutes. Yes, this is a Kemper video, but the principles should apply.

 
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"Is it normal to make a low cut of 450hz for pre-eq? "

I believe this is what TS style boosts do. prob even higher.
 
Dingle said:
"Is it normal to make a low cut of 450hz for pre-eq? "

I believe this is what TS style boosts do. prob even higher.
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Ok, I think I’m starting to wrap my head around this. Correct me if I’m wrong, but the way I’m understanding it is this…

By making my cuts in the amp block on the input eq, I’m essentially altering the tone of my guitar much like a pedal in front of an amp would do. That would explain why the cuts are much more drastic and I’m still retaining decent low end. To my ears, this is producing a fuller and more natural tone than making my cuts in the cab block. I honestly feel like people should experiment with this as well and see how they like the results versus a standard cut at 80hz and 8000hz in the cab block.
 
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