Compression and RMS
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Old 05-07-2017, 01:13 PM   #1
Kayo_2004
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Compression and RMS

Hi all,
Can someone explain how rms works in compression? From what I've read there is peak compression vs. rms compression - what exactly is rms compression and when is it appropriate to use rms compression? I have the Klanghelm DC8C compressor and wanted to learn more about its rms settings. It has a rms knob that is adjustable by milliseconds. The manual for the compressor says that the lower the value on the rms knob, the more the compressor catches peaks so if I turn the knob up, what exactly is that doing? Is it just leveling the track out and ignoring peaks? Thanks for your help!

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Lotus_Jewel (10-07-2017)
Old 05-07-2017, 01:54 PM   #2
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Re: Compression and RMS

Quote:
Originally Posted by Kayo_2004 View Post
Hi all,
Can someone explain how rms works in compression? From what I've read there is peak compression vs. rms compression - what exactly is rms compression and when is it appropriate to use rms compression? I have the Klanghelm DC8C compressor and wanted to learn more about its rms settings. It has a rms knob that is adjustable by milliseconds. The manual for the compressor says that the lower the value on the rms knob, the more the compressor catches peaks so if I turn the knob up, what exactly is that doing? Is it just leveling the track out and ignoring peaks? Thanks for your help!
It mean that the compressor is triggered by RMS level instead of peak level. Now I can't give you a scientific description of what is RMS, but it's sort of a way to measure the average loudness of the track. So when you use RMS compression, the compressor is triggered by that average volume, rather than those sharp peaks. I can imagine it could work quite well on synth groups.

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Old 05-07-2017, 05:44 PM   #3
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Re: Compression and RMS

Means the level detector of the compressor measures the level of signal averaged over a short time window instead of instant peaks. (This is separate from attack/decay settings). Makes for a gentler compressor that, on percussion, would actually leave some of the snappy transients alone, so they can slam into a limiter (or get clipped) if they have to. On synths you could use it as a gentle leveller so only the thick and loud parts are affected. Also on some compressors such as the Alesis 3630/nanocompressor, RMS just sounds more acceptable (I mean peak mode is so terrible ; )

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Old 05-07-2017, 07:11 PM   #4
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Re: Compression and RMS

RMS means Root Mean Square - which is the inverse of the square root of 2. Basically multiply the peak amplitude by 0.707. It's used like Agu said to represent the average amplitude of your sound. Since average amplitude is closer to how we hear loudness than peaks amplitude which often only lasts for short transients.

We can measure more effectively than just multiplying by .707, but that's where the name comes from.

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Old 05-07-2017, 07:32 PM   #5
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Re: Compression and RMS

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Originally Posted by Oatbag View Post
RMS means Root Mean Square - which is the inverse of the square root of 2. Basically multiply the peak amplitude by 0.707. It's used like Agu said to represent the average amplitude of your sound. Since average amplitude is closer to how we hear loudness than peaks amplitude which often only lasts for short transients.

We can measure more effectively than just multiplying by .707, but that's where the name comes from.

> If the waveform is a pure sine wave, the relationships between amplitudes (peak-to-peak, peak) and RMS are fixed and known, as they are for any continuous periodic wave. However, this is not true for an arbitrary waveform which may or may not be periodic or continuous

from [Only registered and activated users can see links. Click here to register]


for those purposes usually a window of a few milliseconds is involved. eg 300ms but could be anything

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Old 05-07-2017, 08:40 PM   #6
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Re: Compression and RMS

Thanks for the replies, these are very helpful! So it would seem then that the rms control on the compressor would be measuring the average loudness of the track based on the settings I specify? For example if I set the knob to 10 milliseconds, the compressor is measuring the average loudness or signal loudness over that 10 millisecond window? Is it doing a look ahead to get this average loudness? So it sounds like it is just meant to level out your audio signal overall based on a window of time that you program into it, correct? You mention it would be good on synth groups and that it is a gentler compressor - what are some other examples of when it is appropriate to use rms compression? Perhaps on a whole track to control its overall loudness? Again, thank you for the replies!
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Lotus_Jewel (10-07-2017)
Old 05-07-2017, 08:53 PM   #7
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Re: Compression and RMS

Quote:
Originally Posted by Kayo_2004 View Post
Thanks for the replies, these are very helpful! So it would seem then that the rms control on the compressor would be measuring the average loudness of the track based on the settings I specify? For example if I set the knob to 10 milliseconds, the compressor is measuring the average loudness or signal loudness over that 10 millisecond window? Is it doing a look ahead to get this average loudness? So it sounds like it is just meant to level out your audio signal overall based on a window of time that you program into it, correct? You mention it would be good on synth groups and that it is a gentler compressor - what are some other examples of when it is appropriate to use rms compression? Perhaps on a whole track to control its overall loudness? Again, thank you for the replies!
I don't mean to sound disrespectful, but this sounds like a "read the manual" moment. It isn't really even possible for us to know since you didn't list the VSTs you are using : ) Now that you know what RMS and Peak are, shouldn't be a stretch to figure out what is what with your software.

It depends on whether the RMS control/setting is a compression type or if it is a meter. An RMS meter isn't going to change the compression type, just give you an RMS "loudness" measurement. Just as an example my limiter has both Peak and RMS meters on it--but these don't affect the type of limiting the VST inacts on the audio signal.

Also, from what I understand, from a technical standpoint compression doesn't control loundess, it controls dynamic range, which in turn affects perceived loudness. A subtle, but important difference. If you want less range between the loudest and and most quiet part of the signal, you would use compression. This can be useful for something like a bassline where certain notes are quieter than others--by decreasing dynamic range you can make it sound like there is less difference in volume between the quiet and loud notes.

I might also be talking outta my ass. Compression is still something I am learning about.

Last edited by relic; 05-07-2017 at 08:59 PM..

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Old 05-07-2017, 11:11 PM   #8
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Re: Compression and RMS

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Originally Posted by -Agu- View Post
It mean that the compressor is triggered by RMS level instead of peak level. Now I can't give you a scientific description of what is RMS, but it's sort of a way to measure the average loudness of the track. So when you use RMS compression, the compressor is triggered by that average volume, rather than those sharp peaks. I can imagine it could work quite well on synth groups.
isnt the threshold for this? you adjust the ceiling? so its a technique for rather specific problems?

I dont use compression much and even though I understand its purpose, i hate how compressed stuff sounds. If you can tell something is being compressed, it has too much compression. thats why my father always said. maybe im biaseD? I have no idea what im talking about. im baked like a cake right now. :notafinga:
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Old 06-07-2017, 01:23 AM   #9
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Re: Compression and RMS

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Originally Posted by Lotus_Jewel View Post
isnt the threshold for this? you adjust the ceiling? so its a technique for rather specific problems?

I dont use compression much and even though I understand its purpose, i hate how compressed stuff sounds. If you can tell something is being compressed, it has too much compression. thats why my father always said. maybe im biaseD? I have no idea what im talking about. im baked like a cake right now. :notafinga:
Imagine it in a way that Peak compression is some invisible junkie on drugs riding the fader up and down like a maniac, hammering down the bits of sound that are trying to jump on his face.

RMS compression is like some guy on his 40s who moves the fader a little bit, leaves it there, takes a sip from his beer, and then places his hand on the fader again.

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Old 06-07-2017, 01:39 AM   #10
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Re: Compression and RMS

Peak compression has a very similar effect to limiting? I think. Not confident.

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Old 06-07-2017, 07:02 AM   #11
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Re: Compression and RMS

I've watched few times compression explanations, and I do understand while the tutorial video goes. As soon as it ends, I have no f idea how compressor works.

But, I find myself using compressors better and better. I set it up by the ear.

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Old 06-07-2017, 08:59 AM   #12
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Re: Compression and RMS

Quote:
Originally Posted by Kayo_2004 View Post
Thanks for the replies, these are very helpful! So it would seem then that the rms control on the compressor would be measuring the average loudness of the track based on the settings I specify? For example if I set the knob to 10 milliseconds, the compressor is measuring the average loudness or signal loudness over that 10 millisecond window?
without looking at the specific compressor you're referencing, chances are the window is fixed as per engineering design. if you're referencing the attack or release knob ("10ms"), that's not the level detector, but another part of the "device". in e.g. Logic's multipressor you have control over the RMS window length, e.g. Peak/RMS in this image [Only registered and activated users can see links. Click here to register]
, but that doesn't mean it's available on every RMS compressor.

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Old 06-07-2017, 09:30 AM   #13
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Re: Compression and RMS

and today I noticed there is a peak button at the top of my ssl mixer, in the compression section. I hear the difference and can relate to the effect. though it wasnt desirable as I use eqing to clean up unwanted freq. The less I use, the better it sounds.
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Old 09-07-2017, 04:50 PM   #14
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Re: Compression and RMS

Hi all, thank you for the replies, I am glad to see others are still learning about compression - as am I! I am unable to post a link from YouTube since I am new here, but I did find a tutorial on YouTube with a mastering engineer explaining that for this particular compressor, the Klanghelm DC8C - the RMS knob on this compressor is used to change the compressor from a "peak" compressor (at the lowest settings) over to an "opto" compressor with the higher settings. So that makes sense based on the descriptions we were all discussing in relation to average loudness.
Again, thanks for your help!
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Old 10-07-2017, 01:19 AM   #15
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Re: Compression and RMS

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Originally Posted by Oatbag View Post
Peak compression has a very similar effect to limiting? I think. Not confident.
so this came from "the secret of the mastering engineer" and as Im reading again, I wanted to share because it relates... or so i felt. keep in mind grain of salt.

dynamics processing:
Both compression and limiting change the peak to average ratio of music, while both tools reduce dynamic range.

compression:
compression changes sound much more than limiting. Think of compression as a tool to change the inner dynamics of music. While reducing dynamic range, it can BEEF up or PUNCH low level and mid level passages to make a stronger musical presence.

limiting:
limiting is an interesting tool. with fast enough attack time 1-2 samples, and fast release 1-3 milliseconds, even several dB of limiting can be transparent to the ear.

consider using limiting when you want to raise the apparent loudness of material without severely affecting its sound.

consider compression when the material seems to lack punch or strength.

REMEMBER - the position of your monitor volume control has a tremendous effect on these matters of judgment. if it sounds properly punchy when you turn up the monitor, then maybe all you need is to turn up the volume rather than add another DSP process.



Okay thats all im sharing for now... but one last idea, someone expressed compression as volume over time. and I thought that was an interesting way to put it, imagine having to actually move all the faders to make the edits as the song unfolds... compression really is pretty rad. its jsut an automated engineer to add or remove volume ... on its most basic idea, at least that is how I see it. like a wait... yes... a shit i just forgot it. what do you call it... yes a gnome... a little gnome who does it for me. lol hahahahaa

I been practicing in my new studio, for the last 6 months Ive had the minimal treatment and size/ratio to actually hear the music with accuracy. but im not done... still got more to do... coming soon.

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