(soft) Limiter (with make-up gain)

[Lloyd]

Hi all; Lloyd Here, using 2.1.3 on a fairly new Windows 10 HP Laptop:
Could someone please explain what a "(soft) Limiter (with make-up gain)" is and how to achieve it and/or manipulate it specifically to achieve increases and decreases in recording volumes.
Thanks. Best to all.

[Trebor]

Could someone please explain what a "(soft) Limiter (with make-up gain)" is and how to achieve it and/or manipulate it specifically to achieve increases and decreases in recording volumes.

When "make-up gain" is selected the waveform is normalized to 0dB after the limiter has been applied :
i.e. it is made as loud as possible after the limiter ...

''make-up gain'' - Yes.gif (97.5 KiB) Viewed 1292 times

If you don't select "make-up gain" the waveform will become quieter after the limiter is applied ...

''make-up gain'' - No.gif (85.11 KiB) Viewed 1292 times

In both cases, (with & without "make-up gain"), the level of compression is the same.
( limiter is a form of compressor ).

[kozikowski]

So it's not really "Make-Up Gain." It's Amplify. Make-Up Gain would return the peaks where they were before the Limiter.

Koz

[steve]

So it's not really "Make-Up Gain."

In the "Limiter" effect that now ships with Audacity (http://manual.audacityteam.org/man/limiter.html), it really is "Make-Up Gain", (not "Normalize").
It looks like that's the effect that Trebor is demonstrating.

In this plug-in, the amount of "make-up gain" is calculated from the amount of reduction that happens to a 0 dB peak. So if the selected settings will apply -6dB to a 0dB peak, then make-up gain applies +6dB of gain (just enough to make up a full-scale signal back to full-scale).

(That's the general idea, but to be totally accurate, Make-up Gain in this effect allows a small "safety margin" and actually makes up to 99.9% of full-scale)

[kozikowski]

actually makes up to 99.9% of full-scale)

Yes, I know the magic that happens around "0dB".

So it may do what I want then. If I intentionally put the show peaks at -3dB and apply a limiter, it might create a "denser" show with the peaks (we assume more of them now) at -3dB.

2.2.1 to follow.

Koz

[steve]

If I intentionally put the show peaks at -3dB and apply a limiter, it might create a "denser"

No that won't do anything.
Limiters are intended to act on sound when a peak exceeds the given threshold, and process the sound so that the peaks don't exceed the threshold. If there are no peaks above the threshold, then nothing will happen.

There are two ways to do what you want (to make a "denser" show). Both do exactly the same thing, but one way takes two step and the other does it all in one.
Starting with a show that has -3dB peak level
First way) Amplify the show to > -3 dB peak level. Apply Limiter with a -3 dB threshold, Make-up gain off.
Second way) Apply Limiter with positive "Input Gain", -3dB threshold, Make-up gain off.

In both cases, positive amplification (gain) is applied first (I'll refer to this as "pre-gain"), so that the overall level is increased, then the peaks are squashed back down to -3dB, giving a "denser" show with a peak level of -3dB.

It's not possible to work out how much "pre-gain" is required, but as a rough estimate, +3dB pre-gain will usually give around +2dB increase to RMS.
If you need more than 2 or 3 dB increase in RMS, then you probably want to consider either applying a compressor first, or re-recording (because your recording level is too erratic).