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Compressors - Auto Make-Up Gain?

VST, AU, etc. plug-in Virtual Effects discussion

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DarkStar
KVRAF
 
6436 posts since 2 Sep, 2003, from Surrey, UK

Postby DarkStar; Fri Feb 24, 2012 11:22 am Compressors - Auto Make-Up Gain?

I would like some guidance, please.

I see that many compressors have a Make-Up Gain control and I can understand what that does. Some have an Auto Make-Up Gain switch too. Could someone explain how this works? How does the plugin calculate how much make-up gain to apply at any point in time?

The User Guide for Sonalksis SV-315 says
Activating the 'Auto-Gain' feature can greatly help in level matching; the makeup-gain is calculated to ensure that a steady-state 0dB input signal will have a 0dB output level, regardless of the compression threshold or ratio.

It should be noted that this feature can produce output signals that exceed 0dBFS, particularly with slower attack time settings, as fast transients may escape compression, but will still have compensatory gain applied. When dealing with high-level signals, it is therefore prudent to ensure that the limiter is activated when the auto-gain feature is used.

Does it just calculate the output level for a 0dB input signal, say x dB, and boost everything by x dB at the output stage? That sounds too simplistic to me.

So:
-- what algorithms are used for Auto Make-Up Gain?
-- Which Compressors do it well, without artefacts, etc?
-- How useful do you find this feature?
Last edited by DarkStar on Sat Feb 25, 2012 5:09 am, edited 1 time in total.
DarkStar
Interesting, if true ...
DaveGamble
KVRian
 
851 posts since 12 Jul, 2009, from Cornwall

Postby DaveGamble; Fri Feb 24, 2012 5:02 pm

DarkStar wrote:Does it just calculate the output level for a 0dB input signal, say x dB, and boost everything by x dB at the output stage? That sounds too simplistic to me.

So:
-- what algorithms are used for Auto Make-Up Gain?
-- Which Compressors do it well, without artefacts, etc?
-- How useful do you find this feature?


Dev here. I worked on the 315Mk2.

Yes, Auto-makeup gain is typically some trivial equation involving the threshold and the ratio. Since you can't predict the spectral density of the input signal, you can't do much better without generating a time-varying compensation gain, and then it wouldn't be autogain... it'd be another compressor.

Dave.
[ DMGAudio ] | [ DMGAudio Blog ] | dave AT dmgaudio DOT com
DarkStar
KVRAF
 
6436 posts since 2 Sep, 2003, from Surrey, UK

Postby DarkStar; Sat Feb 25, 2012 5:08 am

Hello Dave,

Still liking the SV-315 Mk2 here.

I thought that that might me the case :). I was going to post an extract from the Compassion user guide but that seems to be a similar approach.

Thank you for the explanation. So an Auto Make-up Gain feature is an operational convenience rather than essential. You point about "a time-varying compensation gain," reminds me of some articles suggests using two compressors serially, rather than trying to do it all in one.
DarkStar
Interesting, if true ...

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