simulating the sag of tube amps

VST, AU, etc. plug-in Virtual Effects discussion
User avatar
JO512
KVRist
187 posts since 9 Nov, 2018 from Colorado

Post Mon Jun 29, 2020 12:57 pm

The discussion in the thread about Resonant Amp sent me checking my other amp sims to see if they simulate amp sag. They really don't seem to, as far as I can tell.

Resonant Amp thread:
viewtopic.php?f=6&t=545175

I've never played a real tube amp, and so I don't know for sure what the real thing should feel like under my fingers. But reading about sag and listening and playing with Resonant Amp caused me to think that it should be easy to simulate using compressors set up in the right way.

Most here are probably aware of what happens with distortion or saturation, where clipping compresses the signal, essentially putting a ceiling on it. Generally, if the signal is below the clipping threshold, it will remain relatively clean. As you push it against that ceiling, the peaks start getting chopped, either sharply or softly, depending on the distortion.

It seemed to me that in order to simulated sag, one would need to compress the signal after the distortion, but in such a way that when the original clean signal goes really high, the output volume is pushed down even further, making it dip, rather than just flattening out at that ceiling, but perhaps with a bit of time delay. And since the distortion flattens the signal after a certain point, it can't be used as the signal that controls the compression. You need the higher part from the clean signal that is getting chopped off. So I set up Reaper to split the signal before the distortion, sending a clean version to the sidechain input on Presswerk and setting it to use the external control signal.

So the clean signal splits into paths A and B. Signal A goes into your distortion, your amp sim, or whatever and then passes into the compressor to have its volume controlled. Signal B goes into the sidechain input on the main compressor that receives signal A.

It works pretty well when you get it dialed. I am not sure how realistic it is, or whether I really understand sag, but I like the way it feels with certain settings.

The result is that when you play lightly, keeping the signal mostly below the clipping threshold of the distortion, it is cleaner, but relatively loud. When you play harder, it clips more and dips in volume. As you let the note ring, it comes back up in volume as it also cleans up a bit. So you get stronger, chunkier attack, for one thing.

It really feels to me like this is an ingredient in proper distorted guitar tone that I've so far been missing.

imrae
KVRian
1165 posts since 2 Jul, 2010

Re: simulating the sag of tube amps

Post Mon Jun 29, 2020 1:19 pm

There's an interesting airwindows plugin for saggy distortion, have you tried it? https://www.airwindows.com/powersag2/

MogwaiBoy
KVRAF
3550 posts since 26 Nov, 2015 from Way Downunder

Re: simulating the sag of tube amps

Post Mon Jun 29, 2020 6:22 pm

It's a voltage drop in the amp. You need to experience a real tube amp with a tube rectifier! Glorious feeling.

I do kinda think it could be mimic'd in various ways with slow release compression, dynamic filters etc.

Doesn't seem to be a hugely emulated thing in plugin land, unfortunately. Maybe there are some guitar amp simps that do it?

jinotsuh
KVRist
465 posts since 31 May, 2008 from Australia

Re: simulating the sag of tube amps

Post Mon Jun 29, 2020 6:28 pm

There are quire a few that do.

Funkybot's Evil Twin
KVRAF
7367 posts since 16 Aug, 2006

Re: simulating the sag of tube amps

Post Mon Jun 29, 2020 6:38 pm

I find amp sims sound good with a little bit of dynamic EQ afterwards to boost some lows and inversely notch out some mids both dynamically. It adds a bit of movement to the sound that adds some realism. I wouldn't say it's really emulating tube sag but I found it works to emulate the dynamic effect of a cabinet. It's a really nice trick for getting some extra movement out of static cabinet impulses.

User avatar
The Noodlist
KVRAF
2571 posts since 16 Aug, 2017 from UK

Re: simulating the sag of tube amps

Post Mon Jun 29, 2020 7:13 pm

Not entirely ITB.
Watched a video today mentioning creating amp like sag @2.21, but he would say that, he's marketing a product.
https://youtu.be/Xbd2UtNNdRE?list=RDjfQtSWuIsRA
Currently trying to turn noise into music. :neutral:

RafaelMorgan
KVRist
188 posts since 14 May, 2008

Re: simulating the sag of tube amps

Post Tue Jun 30, 2020 4:25 am

Line 6 Helix simulates sag...It's very sensitive to adjustments and not very intuitive, but it gets the job done pretty well once you learn your way around it.
Funkybot's Evil Twin wrote:
Mon Jun 29, 2020 6:38 pm
I find amp sims sound good with a little bit of dynamic EQ afterwards to boost some lows and inversely notch out some mids both dynamically.
Couldn't agree more. Impulse Responses suck (tone). Dynamic EQs after them really help to create a feel of movement. The cabinet section is the most neglected feature in ampsims...

User avatar
JO512
KVRist
187 posts since 9 Nov, 2018 from Colorado

Re: simulating the sag of tube amps

Post Tue Jun 30, 2020 2:38 pm

imrae wrote:
Mon Jun 29, 2020 1:19 pm
There's an interesting airwindows plugin for saggy distortion, have you tried it? https://www.airwindows.com/powersag2/
I'll try it!

MogwaiBoy wrote:
Mon Jun 29, 2020 6:22 pm
You need to experience a real tube amp with a tube rectifier! Glorious feeling.
I do need to experience it! There are too many expensive things I need to buy! :(


jinotsuh wrote:
Mon Jun 29, 2020 6:28 pm
There are quire a few that do.
Do you happen to know of some good ones? I have lots of Amplitube stuff, Guitar Rig, and have tried a lot of free stuff. Nothing I've tried so far has obviously exhibited sag that I've noticed. If there is a super-realistic tube amp sim plugin out there, I'd like to check it out. I recently tried the Kuassa Matchlock plugin, which supposedly does sag, and it didn't seem very compelling to me.

Funkybot's Evil Twin wrote:
Mon Jun 29, 2020 6:38 pm
I find amp sims sound good with a little bit of dynamic EQ afterwards to boost some lows and inversely notch out some mids both dynamically. It adds a bit of movement to the sound that adds some realism. I wouldn't say it's really emulating tube sag but I found it works to emulate the dynamic effect of a cabinet. It's a really nice trick for getting some extra movement out of static cabinet impulses.
Interesting. It might be worthwhile to experiment with using a sidechained clean signal to control a dynamic EQ too. The original clean signal is so much more dynamic than the distorted signal. You can sort of put the dynamics back into the wet signal sidechaining like that, either directly or inversely, depending on whether you expand or compress.

Using envelope followers to control filters could be interesting too.


The Noodlist wrote:
Mon Jun 29, 2020 7:13 pm
Not entirely ITB.
Watched a video today mentioning creating amp like sag @2.21, but he would say that, he's marketing a product.
<span class="skimlinks-unlinked">https://youtu.be/Xbd2UtNNdRE?list=RDjfQtSWuIsRA</span>

Thanks for the suggestion! A regular compressor without a sidechain option to use a clean signal to control the compression amount will achieve this somewhat, but things are much more dynamic if the clean signal can be used to control the gain reduction in the compressor. A simple compressor pedal either before or after distortion doesn't quite get there.


RafaelMorgan wrote:
Tue Jun 30, 2020 4:25 am
Line 6 Helix simulates sag...It's very sensitive to adjustments and not very intuitive, but it gets the job done pretty well once you learn your way around it.

I'd like to try one! Too expensive for me right now though!

HansP
KVRist
232 posts since 9 Sep, 2017

Re: simulating the sag of tube amps

Post Wed Jul 01, 2020 3:20 am

if this is done right, it should deliver a lot of oomph.
plz also check out the free Voxengo TubeAmp, there are two versions that look very different.
I don't know which one is better. but this is about the "bias" knob. it does a little bit into that direction.
perhaps you can combine it with some other distortion plugin that sounds more aggressive.
naturally, the fine-tuning is key, and needs some practical experience with tube amps....

(bias is relevant because it regulates the current that goes through the pair of power valves, and this will change the load on the rectifier.)

Return to “Effects”