FabFilter

Hi -

I'm trying to understand exactly how the gain slider in Pro L works and was curious about whether or not the gain slider is simply a gain/trim knob or if there is something more to it to be aware of.

I already understand that you can hold down shift to make the output knob go down as you pull the gain slider up.

What I'm trying to figure out is, lets say you have something at a fairly steady volume going into the Pro-L (factory default settings) at -15db and you pull the gain slider up 4 dB and leave the output knob set at 0dB. So basically you got a resultant -11 db signal and it is nowhere near hitting or going over 0 dB.

In this case, would this be effectively the exact same thing as using a trim plug in set at +4db, or is the Pro L gain slider coloring or changing the sound in any way?

I ran my own tests by bouncing files of pro-L set as described above vs avid trim set at +4dB and then did a phase flip comparison of the two files and they cancel each other out, so I am thinking the answer is yes.

However, the manual for the fab filter describes the gain slider as follows: "The gain slider adjusts the threshold of limiting and the increase in output gain at the same time."

So I am wondering if there are other scenarios I need to be aware of where my phase flip testing might not hold up, aside from the obvious scenario where the signal is going above wherever the output knob is set at.

I think what they mean by threshold in their description of the gain slider is that if you increase the gain slider, you are pushing the signal toward whatever you have your output knob set at, so the higher you push the gain slider, the more of the signal you are pushing over the setting of the output knob, effectively adjusting the "threshold" level. But in that case the idea of a threshold would only apply if you are actually pushing the signal above whatever the output knob is set at.

Am I interpreting this correctly?

Thanks!

Hey,

I tried doing your test myself.
I took a -30dB Sine wave, on 2 different tracks, and flipped phase on one of them.
In the first track I used Cubase's gain knob on the channel strip, and on the other I used pro-L.

When I gave each one of them +6db, they canceled each other out, but not completely.
The analyzer (RME Digicheck) showed a -107db level, which sounds like a complete null, but it isn't
Digicheck calls a 'null' anything bellow -150dB, if I'm not mistaken.

When I gave both of them a +24dB of gain, the analyzer showed -85dB.

So it seems that the gain slider does change a little, very little.

I'm not sure that a sine wave is the ultimate check, though :}

Cheers

It's just increasing input gain. Output is post gain. That's really it... The manual's phrasing is a bit confusing but you're over-analyzing it.

Some other limiters have you adjust the threshold instead, like a compressor, and you apply makeup gain. With Pro-L the threshold is 0 and you're just increasing gain to dial in the amount of limiting. It's nice like this because you make it louder all the way instead of quieter first. The alt control (not shift like you wrote) is so you can hear the part of the signal that's limited.

With the phase test it will cancel out perfectly as expected. I've done this as a sanity check in the past. You may need to enter the exact value instead of sliding the knobs. There's human error in your test because the results make no sense.

Hey Booli

I did enter exact values, of course.
Results indeed don't make sense, but I couldn't find out why.

When not using Pro-L there's complete null, when using it there's still a tiny tiny signal.

I agree that in the end, it doesn't matter :}

Cheers

It's probably the noise floor from another source.

Hi Yroth and Booli thanks for the info!