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Author Topic: Converting peak limiter to RMS limiter  (Read 1017 times)

Tim McCulloch

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Re: Converting peak limiter to RMS limiter
« Reply #20 on: October 08, 2018, 08:18:27 pm »

I think the terminology gets butchered a bit between manufactureres, publications, forums, etc. I'm trying to see through the veil  :)

I was trying to state that with the HPF set according to manufacture recommendation over excursion would be taken care of.

Taken from Nick here:
https://soundforums.net/community/threads/help-me-understand-system-limiting-setting-it.1139/page-2

There's also talk of a difference between a true RMS limiter and a thermal limiter.

Perhaps there is no need for an additional rms/peak limiter when using a thermal limiter and the amp can't send peak voltage?

I think there is some conflation of terms as used... but almost all of those criteria have a direct influence on the transducer holding together physically and thermally.  The interaction a fixed HPF filter and *any* type of voltage limiter is just that, a fixed relationship.  When one gets into processing that uses variable HPF or other filters, one must be able to measure the acoustic result of the electrical variables and decide if the protection is sufficient, too aggressive or ineffective... or too audible/inaudible.

What is your goal here?  Protection against stupid operation - i.e. DJ-proof, or squeezing the last couple of dB out of a pass band, when operated by mindful mixerpersons?
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Ivan Beaver

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Re: Converting peak limiter to RMS limiter
« Reply #21 on: October 09, 2018, 07:12:14 am »



What is your goal here?  Protection against stupid operation - i.e. DJ-proof, or squeezing the last couple of dB out of a pass band, when operated by mindful mixerpersons?
This is a VERY important statement.  With different settings.

But many people want to "squeeze every last watt" and also drive the system as hard as it can be, compression/limiting be damned.

Those are NOT things that happen at the same time.

Often choices have to be made for specific situations.
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Nathan Riddle

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Re: Converting peak limiter to RMS limiter
« Reply #22 on: October 09, 2018, 01:03:04 pm »

I was trying to stay manufacture & limiter values agnostic as I was mostly curious about the differences between RMS & peak limiting circuitry/algorithms.

My goal is to implement the manufacture recommended limiting values.

Quote
RMS Limiter: 80 Volts
Thermal Limiter: 40 volts, 3.0 Seconds Attack, 1.0X Release (multiplier of Attack)
XMax Limiter: 60 Volts at 25 Hz

I just thought of a way to do the XMax limiter. Grab the impedance chart and calculate @ that frequency the...nevermind.

Would a limiter set at 60 volts with Attack of 40ms (25hz) work for XMax?
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Frank Koenig

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Re: Converting peak limiter to RMS limiter
« Reply #23 on: October 09, 2018, 01:28:17 pm »

with Attack of 40ms (25hz) work for XMax?

I keep my peak voltage limiters set to essentially zero attack time. They're there to protect against dropped mics, phantom power pops, and similar accidents. I never expect to hit them during normal operation. But that's just me.

I also fail to see the distinction between RMS limiters and thermal limiters. What's the purpose of an RMS (or other average power proxy) limiter if not to prevent overheating of the voicecoils?

--Frank
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David Morison

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Re: Converting peak limiter to RMS limiter
« Reply #24 on: October 11, 2018, 03:39:27 am »

I was trying to stay manufacture & limiter values agnostic as I was mostly curious about the differences between RMS & peak limiting circuitry/algorithms.

My goal is to implement the manufacture recommended limiting values.

I just thought of a way to do the XMax limiter. Grab the impedance chart and calculate @ that frequency the...nevermind.

Would a limiter set at 60 volts with Attack of 40ms (25hz) work for XMax?

I'm curious what kind of speaker this is that needs an extra limiter for frequencies that low - I know Ivan pointed out how the HPF could be rendered less effective, but surely unless this is an infra sub or studio monitor, you are going to have an HPF higher than 25Hz in place already, right?

Anyhoo, 40ms is one whole wavelength at 25Hz, therefore if your limiter only kicks in after 40ms you've already let one cycle through to the driver, including one positive and one negative peak (assuming something remotely resembling a sine wave at least).

If you want to prevent the first peak coming through, you'd need to have an attack set to 1/4 wavelength at the longest, depending on how quickly the limiter responds after the attack time has passed.

FWIW,
David.
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Nathan Riddle

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Re: Converting peak limiter to RMS limiter
« Reply #25 on: October 11, 2018, 09:37:20 am »

I'm curious what kind of speaker this is that needs an extra limiter for frequencies that low

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David Morison

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Re: Converting peak limiter to RMS limiter
« Reply #26 on: October 11, 2018, 11:48:22 am »



That quotes 40Hz, not the 25Hz in your earlier post...

But, that wasn't really the point - which was that your limiter would need to kick in at no later than 1/4WL of the frequency of interest.
« Last Edit: October 11, 2018, 11:55:57 am by David Morison »
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Nathan Riddle

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Re: Converting peak limiter to RMS limiter
« Reply #27 on: October 11, 2018, 11:59:54 am »

That quotes 40Hz, not the 25Hz in your earlier post...

But, that wasn't really the point - which was that your limiter would need to kick in at no later than 1/4WL of the frequency of interest.

The other quote was TH118's suggested limiter preset. TH115 is what I was building presets for.

But good point about the 1/4WL.

The answer to this question is there's no way to convert between the two. And to not use the peak limiter in the PLD as it's useless in this situation (amp self-limits).
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Frank Koenig

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Re: Converting peak limiter to RMS limiter
« Reply #28 on: October 11, 2018, 01:26:08 pm »

I've seen that table in other literature I've downloaded from Danley. I'm guessing the "x-max limiter" is a peak limiter downstream of a low-pass filter that attempts to model the (approximately inverse square) relationship of excursion and frequency. That relationship gets interesting near the lower cutoff and is very different for different types of speakers -- bass reflex, closed-back horn, other horns, etc.

I'd be happy if Ivan would give us the long, complicated, and correct version of what those limiter settings mean.

--Frank
« Last Edit: October 11, 2018, 01:48:25 pm by Frank Koenig »
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Nathan Riddle

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Re: Converting peak limiter to RMS limiter
« Reply #29 on: October 11, 2018, 02:29:23 pm »

I've seen that table in other literature I've downloaded from Danley.
snip
I'd be happy if Ivan would give us the long, complicated, and correct version of what those limiter settings mean.

--Frank

Agreed.

I would like to know what (nominal) impedance the values are for. It would make a difference between an 8 ohm sub and a 4 ohm sub.
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