SC-C S Compressor - when or how to use ?

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dante
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SC-C S Compressor - when or how to use ?

Post by dante » Fri Jan 03, 2014 12:46 pm

This is the stock SC-C S compressor that comes stock with Scope 5.x
SC-C S.jpg
SC-C S
SC-C S.jpg (18.76 KiB) Viewed 2914 times
Now when I tried it out, the Loudness seemed to just boost the volume same as turning the input up. And there are no more controls.

For ScopeRise, does anyone know what this would be usefull for (eg low DSP scenarios?), and given there's no usual ratio / threshold controls, would that imply that the 'Loudness' is somehow a combination of ratio / threshold ?

fra77x
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Re: SC-C S Compressor - when or how to use ?

Post by fra77x » Fri Jan 03, 2014 12:53 pm

It performs the basic function of the compressor. Lowers high levels, boost the low levels so to reduce the dynamic range. The input is the ratio and the loudness the boost. (i haven't used it but propably i'm right). It is not for low dsp scenarios. It is for setups that you want that type of standard compression.


If you often use a compressor you understand that after a while you always put the threshold at a certain height and then you just raise the gain 6dB so to compensate for the reduced peaks, and that way the signal gets compressed dynamically. So the next logical step is to omit alltogether the threshold pot, omit the ratio, and get a input gain instead that will act as the threshold/ratio. The loudness is the gain at the end of the chain.

Eanna
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Re: SC-C S Compressor - when or how to use ?

Post by Eanna » Fri Jan 03, 2014 1:30 pm

My understanding of Loudness is around equal-volume curves - the old Fletcher-Munson curves.
Basically, humans don't perceive sounds to be equally loud across the frequency spectrum. At a particular dBFS (sound pressure levels), sweeping a sine wave from the lowest to the highest frequencies, bass frequencies will be quiet, and the higher frequencies. Loudest sound perceived by our ears are in the middle of the spectrum.
This is tied in to the difference between white noise and pink noise - white noise is equal volume across the spectrum, pink noise is non-equal volume across the spectrum - there's a significant dip in the mid range, to accommodate our enhanced perception of loudness in that range.
This is also why compressors react so much to bass frequencies. Compressor detector circuits don't react to the intensity of the sound in the same way that our perception of sound does - what sounds like a relatively-quiet bass part to us is a loud signal to a compressor. Maybe some compressor detector circuits have an inverse-smile shape - which you would expect to perform a 'levelling' function - but I don't know if any compressor does do that.
Furthermore, for Spectrum Analyzers, you'll notice that these can react to bass frequencies, showing significant peaks in levels for bass and treble frequencies, when you ear isn't perceiving it. A good spectrum analyser will have various modes to compensate for equal-loudness curves..

So, this Loudness setting in the device - it's to accommodate Fletcher-Munson curves, the effect of our perception of sound. Basically, it's in effect a smile-type eq - increasing the levels of the bass and treble frequencies. Without being 100% sure, I would say that Loundness value of 0% is a flat eq, and a Loudness value of 100% is basically an eq in the shape of the graph of a Fletcher-Munson curve.

So is this a good thing, I hear you ask? Why provide such a setting?
Well, these equal-loudness curves are dependent on the overall sound pressure levels too. The effect of these curves is such that, at quieter overall volumes, bass and high frequencies are even 'more' attenuated by our perception. You'll notice that on your own monitoring equipment - turn the volume down, and you lose your bass and top-end, but the mids are still easily perceived.

So, if you're passing a quiet part thru this device, you will want to increase the "Loudness" setting.

I think I'm right about this. Anyone who cares to correct me in any way, feel free.
Not because it is easy, but because it is hard...

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garyb
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Re: SC-C S Compressor - when or how to use ?

Post by garyb » Fri Jan 03, 2014 1:31 pm

the harder the input signal hits, the more compression. the loudness control is for makeup gain, so the the peaks remain the same.

it's a basic compressor similar to many dBx units or an LA2.

Eanna
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Re: SC-C S Compressor - when or how to use ?

Post by Eanna » Fri Jan 03, 2014 1:34 pm

Here's the current ISO equal-loudness curve. Fletcher and Munson originally experimentally drew graph damn-similar to these when they started to investigate this, way back in the 1930's.

http://en.wikipedia.org/wiki/File:Lindos1.svg
Not because it is easy, but because it is hard...

fra77x
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Re: SC-C S Compressor - when or how to use ?

Post by fra77x » Fri Jan 03, 2014 1:57 pm

Eanna because a compressor is always a compressor and is never an equaliser, me and Gary are right and you are wrong. ;-)

http://en.wikipedia.org/wiki/Dynamic_range_compression

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Re: SC-C S Compressor - when or how to use ?

Post by Eanna » Fri Jan 03, 2014 2:03 pm

They shouldn't have called it loudness then ;-)
Not because it is easy, but because it is hard...

fra77x
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Re: SC-C S Compressor - when or how to use ?

Post by fra77x » Fri Jan 03, 2014 2:13 pm

Because it is easy...

"The perception of loudness is related to both the sound pressure level and duration of a sound."

"Common uses

Compression is often used to make music sound louder without increasing its peak amplitude. By compressing the peak (or loudest) signals, it becomes possible to increase the overall gain (or volume) of a signal without exceeding the dynamic limits of a reproduction device or medium. The net effect, when compression is applied along with a gain boost, is that relatively quiet sounds become louder, while louder sounds remain unchanged."

"Compression can also be used on instrument sounds to create effects not primarily focused on boosting loudness. For instance, drum and cymbal sounds tend to decay quickly, but a compressor can make the sound appear to have a more sustained tail. Guitar sounds are often compressed in order to obtain a fuller, more sustained sound."

"Record companies, mixing engineers and mastering engineers have been gradually increasing the overall volume of commercial albums. The greater loudness is achieved by using higher degrees of compression and limiting during mixing and mastering; "


An equalizer is a frequency dependant gain control

A compressor is an amplitude dependant (peak), or loudness dependant (rms) gain control
Last edited by fra77x on Fri Jan 03, 2014 2:29 pm, edited 1 time in total.

Eanna
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Re: SC-C S Compressor - when or how to use ?

Post by Eanna » Fri Jan 03, 2014 2:28 pm

Thanks for your quotations. I know what a Compressor is.

Do you see how a device that implemented a scalable Equal *Loudness* Curve would be useful in a device designed to maximise RMS loudness?

http://en.wikipedia.org/wiki/Loudness_compensation
http://en.wikipedia.org/wiki/Equal-loudness_contour

...and like I say, I'm happy when I'm wrong. Means I'm learning something. Just wish I was wrong more often lol
Not because it is easy, but because it is hard...

fra77x
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Re: SC-C S Compressor - when or how to use ?

Post by fra77x » Fri Jan 03, 2014 2:59 pm

You can meet me... you will be happy every day! :D

hubird

Re: SC-C S Compressor - when or how to use ?

Post by hubird » Fri Jan 03, 2014 3:46 pm

nowhere Eanna said or suggested a compressor is an equaliser :)
If the F-M curve is in play, then indeed the result looks like a inverse smilie curve on a graphic equalizer.

You better could have said 'a compressor isn't a psycho-acoustic processor', like the PsyQ or the original the Vitalizer.
Indeed those bring the F-M curve into the mix.
I doubt if the loudness knob on the compressor refers to that curve.
So Eanna has a point by saying they shouldn't have called the knobfunction 'loudness'.
The usual 'Gain' or 'Make-up' would habe been better then.

Yet, lower emphasized mid frequencies makes the extremes on the fr. scale relatively 'louder'.
Here both effects meet, but a compressor changes the ratio between loud and soft, which the PsyQ or similar effects don't.

It still could be this Loudness knob does it's compressing work while implementing the F-M curve at the same time, I dunno.
Kind of an extra quality of the design, although that would surprise me with such a minimized basic compressor.

The test for the loudness knob would of course be, turn the input down untill equal input/output, then boost the loudness, record it, and compair the original and precessed file, after having equalled the (peak) volume of both files.
In an sequencer it works best by instant switching between two solo'd tracks on the fly.
There shouldn't be a difference, if I'm right.
If you hear relatively less mid at the same volume then the knob does real loudness, F-M curve like.

fra77x
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Re: SC-C S Compressor - when or how to use ?

Post by fra77x » Fri Jan 03, 2014 4:29 pm

ok :-? :lol: :P

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garyb
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Re: SC-C S Compressor - when or how to use ?

Post by garyb » Fri Jan 03, 2014 4:33 pm

using fletcher munson curves on a compressor's eq would only make sense if the music was meant to be listened to at a specific volume. phon curves are a measure of the human ear's frequency response at different sound levels. they are important in that they show that the human ear becomes more sensitive to bass as volume increases. what's so important about this is the reason why to mix a moderate, even low volumes.

in the '70s, there was a proliferation of small studios with "engineers" that had never actually become engineers. instead they were people who either bought gear and/or had been in a studio, but they had not studied audio, acoustics or electronics formally. at the same time, large amps and speaker systems for studios were suddenly available cheaply. the result was that the "engineers" tended to do awesomely loud and huge mixes for their clients on big systems. these mixes sounded great, but when the volume was lowered, the low end in the music disappeared. this led to a "loudness" button, which added low mids and bass, being built into almost every home stereo(and it took about 10-15 years for those to disappear, although not completely). i know the people who hang out here are mostly too young to remember these things....

anyway, the phon curves are taught about because they show why it's better to mix at low volumes. if the music is mixed at a low volume, the amount of bass that sounds correct seems to get bigger as the playback volume increases. mixes that were done at very high volumes seem to lose bass as the playback volume lowers.

the "loudness" control on the compressor however, is about the average volume of the signal. if the signal's peaks are reduced, then they are closer in level to the of the lowest volume sections. when gain is added to make the peaks the same level as before processing, the overall loudness increases, because the average level increases.

hubird

Re: SC-C S Compressor - when or how to use ?

Post by hubird » Fri Jan 03, 2014 4:39 pm

I remember...shi-it! I'm old :D

what's phon? I know there are different curves for different volumes, but phon?

-edit, googled it already, it's a unity.
But then what is an iphon?

@Fra, hehe :)
Last edited by hubird on Fri Jan 03, 2014 4:58 pm, edited 1 time in total.

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Re: SC-C S Compressor - when or how to use ?

Post by garyb » Fri Jan 03, 2014 4:58 pm

yep, a Phon curve is a Fletcher-Munson curve.

hubird

Re: SC-C S Compressor - when or how to use ?

Post by hubird » Fri Jan 03, 2014 5:08 pm

yes: http://en.wikipedia.org/wiki/Equal-loudness_contour
I always mix at rather low levels (except at late afternoon when I activate the ADAM woofer for volume testing).
Not because of the F-M curve but because the neighbours below me :D

It's good you've mentioned there isn't one F-M curve.
I'm into mastering these days, it's important to realize that when it sounds good at lower levels on a good soundsystem (for hidden subs), then it probably sounds good at loud levels.

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Re: SC-C S Compressor - when or how to use ?

Post by garyb » Fri Jan 03, 2014 5:13 pm

that's right.

Eanna
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Re: SC-C S Compressor - when or how to use ?

Post by Eanna » Fri Jan 03, 2014 5:14 pm

I suggested that the loudness knob be used for quiet tracks in mix..
Not because it is easy, but because it is hard...

fra77x
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Re: SC-C S Compressor - when or how to use ?

Post by fra77x » Fri Jan 03, 2014 5:31 pm

For several years > 10 i had the same reaction to compression. I couldn't understand how the compressors i had in my hands, that appeared to me like a gain control and nothing more, was the "important" compression function. Their is a misconception trainee enginneers and musicians carry from the overtones of the analogue devices period that a "good" compressor magically transforms your sound to something powerful and artistically good. It took me several years of experiment, studying and failing to slowly start to understand the actual usage of these devices on audio material and that there are specific procedures that engineers apply to their audio so to make it aesthetically nice. The most important thing to point is that there are different usages of the dynamics devices and each one has an important role in sound recording, mixing, production and mastering.

Mixing at low levels is crucial, so to achieve smooth and professional sound at the end.

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Re: SC-C S Compressor - when or how to use ?

Post by dante » Fri Jan 03, 2014 11:34 pm

This is great stuff guys and I intend to distill it into scoperise article, but I am looking to sum up in a single sentence or maybe 2 or 3, how this compressor works, with less controls than most of the others many would be used to.

So, from a beginners point of view, would the following sum it up about the controls on this compressor :

"This is a basic compressor where the 'Input' control serves a similar function to 'Ratio and Threshold' on other Scope compressors, and 'Loudness' would be similar to 'Make Up Gain'."

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