Old 11-30-2015, 03:50 AM   #1
mschnell
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Default Realtime Brick Wall Limiter

Hi Experts,

I am using Reaper for live playing with VST Instruments.

Some of same sometimes produce rather excessive Peaks, but I can't simply turn them down, as the balance with other instruments needs to be granted.

So I think it would be a good idea to insert a brick wall limiter VST in the signal flow.

Other than with recording for this low-latency application this can't be a look ahead type algorithm, but just a simple plain old limiter.

Moreover it should not use up much CPU for this rather simple purpose. (Could be done with a JSFX but a VST will perform better on that behalf).

Does it make sense to use ReaComp ? (how to set it to be a plain limiter ?) Or is there something easier / more dedicated / better suitable ?

-Michael
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Old 11-30-2015, 04:19 AM   #2
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Hi Michael,

brickwall limiter, which will avoid sample peaks over 0dBFS at output, with zero lookahead time becomes essentially a clipper.
So although you can place such thing at your master bus, it won't sound much nicer than clipping of your converter.. at least for its attack phase, where it will produce shitload of odd order harmonics (eg. sine became square).
That's why even old digital limiting algorithms had some lookahead and in most cases also oversampled detector signal. Original 20y old L1 has 64 samples (1,3ms) of processing latency @48k IIRC.. similarly dedicated hardware boxes by TC or Jünger for instance.
Analog limiters or limiting amplifiers as they were also called, were essentially compressors with very quick attack time constant and high ratio.. Inherently there wasn't any latency, but there is one important difference, downstream analog devices (eg. mixers, tape recorders) easily accepts very short peak values, which passed through limiter, without any problem or audible degradation as opposed to digital devices, where even 3 sample long peak cause clipping and illegal signal.

So there are basically two choices for you IMO..
Either accept additional latency (even in case of ReaComp there is adjustable lookahead for such uses)..
Or even better (IMO) if you don't want to alter balance of instruments, as you wrote.. Simply turn down master bus fader to have sufficient headroom at your output and compensate for that at your amp or headphone amplifier.

Michal
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Last edited by msmucr; 11-30-2015 at 04:37 AM. Reason: typo
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Old 11-30-2015, 04:21 AM   #3
Nizhny Tagil
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Quote:
Originally Posted by mschnell View Post
Hi Experts,

I am using Reaper for live playing with VST Instruments.

Some of same sometimes produce rather excessive Peaks, but I can't simply turn them down, as the balance with other instruments needs to be granted.

So I think it would be a good idea to insert a brick wall limiter VST in the signal flow.

Other than with recording for this low-latency application this can't be a look ahead type algorithm, but just a simple plain old limiter.

Moreover it should not use up much CPU for this rather simple purpose. (Could be done with a JSFX but a VST will perform better on that behalf).

Does it make sense to use ReaComp ? (how to set it to be a plain limiter ?) Or is there something easier / more dedicated / better suitable ?

-Michael
Isn't there a JS Utility Limiter with just one slider to set the max vol output? Those tools usually run light as a feather.

There's plenty of choice from the JS (LOSER's stuff, schwa's soft clipper...), but if you want to use ReaComp to tame peaks, you could just set all the time constant to zero, ratio at inf:1, threshold as needed and check the "Limiting" option, slighly tweaking the RMS and Knee if you want a softer effect.
EventHorizon has a look-ahead feature, so maybe it's not what you want.

There's a ton of other free and lightweight VST limiters around and the mostlightweight I can think of are Yohng's W1 and the Classic Limiter, but I'm not sure they don't do look-ahead.

EDIT: as explained above, all of these should add distortion, of course.
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Old 11-30-2015, 04:28 AM   #4
Joaquins Void
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I think reacomp should work. I am fairly certain it doesn't use lookahead unless pre comp is on.

Set the ratio to inf, and the RMS to zero, and you have a peak limiter.
Leave the attack at about 3 ms and the release at about 100ms.
Then check the "Limit output" checkbox.

I.e, it's good to have some attack to avoid distortion, but if something should make it through faster than that, the "limit output" option means it will basically be clipped.
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Old 11-30-2015, 04:29 AM   #5
Stews
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FYI, every 1ms of latency is like moving the speakers 1 foot further away. So if you would find it acceptable to move the speakers 1.3 feet further away in order to solve your clipping, you could just use the lookahead limiter.
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Old 11-30-2015, 06:20 AM   #6
mschnell
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Thanks for all Input.

I'll do some tests....


later:

I set up ReaComp with Infinity, -1 db Limit, 0.5 mSek Attack, and 1 mSek preview.

Works great !

-Michael

Last edited by mschnell; 11-30-2015 at 11:25 PM.
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Old 11-30-2015, 11:10 PM   #7
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Search for MGA in the fx browser. Two versions pop up. Take your pick. Nolatency, smooth release.

I use that when I'm mixing, but all that does is catch the ocassional peak to protect my outputs.

Having little to none of the signal reach the ceiling is always the best precaution. When rendering I use a 4x oversampling Elephant limiter by Voxengo in El Uni mode.
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