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Stuck in the Glue

Postby Gone To Lunch » Mon Aug 20, 2018 10:29 am

I am studying the Glue compressor by Cytomic, which has a both a range control and a mix control, and is based on the SSL G.

https://cytomic.com/#plugins


The manual says :

“Range (dB): 0 to Full (-oo)
The Range Knob is a very useful addition to the original design, it allows you to limit the depth of compression and maintain a more natural sound. Since transients typically have the highest peaks in audio the Range Knob has a large effect on their sound, but also limits the total compression depth possible.
After analysing the SSL 4000* circuit it was found that various control voltages were limited at a fixed amount. The Range Knob provides a way to vary this limiting action which is such a key aspect in why the analog compression circuit sounds so good.
Any setting can be made more subtle with the Range Knob. It allows you to still grab the sound early but then off to not over-compress. This makes a great alternative to parallel compression with the Mix Knob.
As a guide use values from -60 dB to -80 dB to emulate the original characteristics of the compressor, and values of around -15 dB to -40 dB as an alternative to using the Mix knob.”

and

“Mix (%): Dry 0 to Wet 100
This control mixes the dry signal phase accurately with the compressed signal pre Peak Clip so you can achieve parallel compression amounts.
The knob shows you a linear percentage of operation, which fine adjustment on either end and more coarse adjustment near 50% which more closely matches a dB gain knob.”

So my question is, what is the relationship between these two ? If I use a value of “around -15 dB to -40 dB as an alternative to using the Mix knob”, how does that play with the Mix control ?

I have tried a lot of tweak and twirl, but can’t quite discern how they interact ?
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Re: Stuck in the Glue

Postby desmond » Mon Aug 20, 2018 10:34 am

I would see that as the range control is almost like a "compression amount %" - at full/100%, the compressor acts as the controls are set, but as you dial it back, the amount of compression to that signal is reduced accordingly. All this is on the compressed signal.

Mix just mixes between the original dry signal, and the compressed signal. It has no bearing on the compressed signal or changes it's characteristic in any way - it's just a mix between the dry signal, and whatever the compressed signal is doing based on the compressor control settings.

So the two controls do very different things.

Does that help?
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Re: Stuck in the Glue

Postby Hugh Robjohns » Mon Aug 20, 2018 10:44 am

It doesn't. They are entirely separate controls performing entirely different functions.

The mix control blends a (usually very over-) compressed signal with the original -- an arangement known as parallel compression (sometimes also London or New York compression). This has the effect of creating 'bottom-up compression' where the loud transient peaks are largely unaffected, but the quieter bits are raised in level -- reducing the overall dynamic range but without altering the delicate transients.

Image

This is in complete contrast to normal 'top-down compression', which inherently alters the loud transients as it rushes to apply the required gain reduction.

Image

Consequently, parallel compression is very popular in mastering as it has a much more subtle sound character than conventional compression. It is also often used to reduce the dynamic range of drum tracks and drum stems as it preserves the transient attacks.

I'm not very familiar with the Cytomic compressor, but it sounds like the Range control is doing the same as the range control on an expander, and simply restricting the maximum amount of gain reduction that can be applied when heavily driven.

If you imagine the transfer plot (input level on the horizontal axis plotted against output level on the vertical axis), a normal linear system would measure as a straight line at 45 degrees. Introducing a compressor would cause that line to tilt down above the threshold, with higher compression ratios causing the slope to tend towards levelling off.

compressor range.png


With a range control, the plot would take on an S-curve instead, initially reducing the angle before straightening up again. So the mid-range sound levels get compressed, but low level and high level stuff is unaffected. In that way, transients are preserved (because they are not being controlled), but the bulk of the material is having its dynamic range reduced.


Hope that helps.
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Re: Stuck in the Glue

Postby Gone To Lunch » Mon Aug 20, 2018 11:37 am

Thanks for your replies. I can see I have got more homework to do !

What set me off was the phrase re Range control in the manual :

"As a guide use values from -60 dB to -80 dB to emulate the original characteristics of the compressor, and values of around -15 dB to -40 dB as an alternative to using the Mix knob.”

So if I want to experiment with using it as 'an alternative', do I set the Mix knob to 100% dry or wet, or what ?

If Range is working like a range control on an expander, is that on the combined wet/dry signal, ie the output from the mix knob, or is it before the mix knob ?

Or something else ?

There is a signal flow chart on p5 of the manual, see link - but I can't figure out the path ?

https://cytomic.com/files/TheGlue-Manual.pdf
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Re: Stuck in the Glue

Postby desmond » Mon Aug 20, 2018 11:47 am

Gone To Lunch wrote:So if I want to experiment with using it as 'an alternative', do I set the Mix knob to 100% dry or wet, or what ?

Not using the mix knob in this context means not mixing in the dry signal at all, so 100% wet, listening to the compressed signal only.

But I'm not posh like Hugh and have no swanky graphs to display... :frown: :tongue: :wave:

*All* of the compressor controls affect the the compressed signal output.
None of the compression controls change the dry signal.

Gone To Lunch wrote:There is a signal flow chart on p5 of the manual, see link - but I can't figure out the path ?

That's p7. The mix block takes in the compressed signal, and the dry signal, and has a knob that mixes the two together according to the knob position. That's it.
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Re: Stuck in the Glue

Postby CS70 » Mon Aug 20, 2018 11:59 am

Gone To Lunch wrote:So if I want to experiment with using it as 'an alternative', do I set the Mix knob to 100% dry or wet, or what ?

Don't have that compressor, but if I did, and read the same as you do in the manual, my take would be that they mean these are two alternative ways to get a subtler sonic effect while still achieving the compression you want. Two different ways to achieve the same overall aim but (possibly, as I haven't heard the comp) with a bit different sonic result.

That given, I would set mix to 100% _wet_ (i..e the compressor does it thing) and try the range control. If your compressor is 100% dry, you'll hear only the original signal. :-)
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Re: Stuck in the Glue

Postby Hugh Robjohns » Mon Aug 20, 2018 12:36 pm

Gone To Lunch wrote:What set me off was the phrase re Range control in the manual :

"As a guide use values from -60 dB to -80 dB to emulate the original characteristics of the compressor, and values of around -15 dB to -40 dB as an alternative to using the Mix knob.”

So if I want to experiment with using it as 'an alternative', do I set the Mix knob to 100% dry or wet, or what ?

Yes, It's an alternative to the Mix (parallel compression) mode that achieves a similar-sounding effect (assuming you get the threshold setting right!).

So with a reduced Range setting, the transient peaks are left uncompressed -- much like the parallel compression mode -- and hence it serves as an alternative with a similar sound character.

If Range is working like a range control on an expander, is that on the combined wet/dry signal, ie the output from the mix knob, or is it before the mix knob ?

It affects the output of the compression element of the signal path only. The mix control is a bypass path around the compression element which allows the input (dry) signal to be recombined with the compressed (wet) signal. If you're using the reduced range idea, you just want to hear the compressed signal on its own, so 100% wet on the mix knob.

There is a signal flow chart on p5 of the manual, see link - but I can't figure out the path ?

Page 7. https://cytomic.com/sites/cytomic.com/files/TheGlue-Manual.pdf The upper blue box is the audio path. The bottom blue box is the side-chain. The 'amp' in the upper box is the compressor's gain-control element, with the Mix function following it to combine the input signal with the compressed signal for parallel compression effects.

The side-chain uses a feed-forward topology, normally analysing the input signal (although that can be replaced by an external signal for 'auto-ducking' or 'voice-over' applications).
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Re: Stuck in the Glue

Postby Gone To Lunch » Mon Aug 20, 2018 1:28 pm

Thank you so very much.

Now I understand it !

(I said p5, because that is in the one I have, the online manual has been subsequently edited.)

For the benefit of anyone thinking of getting this compressor, I am very happy with it - it can sound great ! I am not complaining about it at all ! I have had it a couple of years, but only ever used it with the comprehensive presets. Then I chanced upon the compression archive elsewhere in this forum and decided to dig a little deeper and then fell in !
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Re: Stuck in the Glue

Postby Hugh Robjohns » Mon Aug 20, 2018 4:09 pm

:thumbup: :D
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Re: Stuck in the Glue

Postby Zukan » Tue Aug 21, 2018 8:14 am

I don't know how may times I go back to Glue when I need that nice SSL MB sheen .....it just works.
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Re: Stuck in the Glue

Postby The Bunk » Tue Aug 21, 2018 4:28 pm

Well for what it's worth, Hugh's posts on this have enlightened me as to the "Master Bus NY Comp" plug-in in Reaper; I'm naturally assuming that NY means New York?!?! Thank you if so!
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Re: Stuck in the Glue

Postby James Perrett » Tue Aug 21, 2018 4:57 pm

The Bunk wrote:Well for what it's worth, Hugh's posts on this have enlightened me as to the "Master Bus NY Comp" plug-in in Reaper; I'm naturally assuming that NY means New York?!?! Thank you if so!

I'm assuming you mean the preset for ReaComp - it is a good introduction to parallel compression but I find it needs tweaking a bit for most material that I work on.
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Re: Stuck in the Glue

Postby The Bunk » Tue Aug 21, 2018 5:30 pm

Thanks James - Yep, that's right...
Unless it's just me, I nearly always tweak the Reaper compression presets using a combination of eyes and ears!
Not wishing to hi-jack the thread, but would I also be right in assuming that the ability to adjust "wet" and "dry" levels in their compression plug-in is basically parallel compression?
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Re: Stuck in the Glue

Postby Hugh Robjohns » Tue Aug 21, 2018 6:55 pm

The Bunk wrote:Unless it's just me, I nearly always tweak the Reaper compression presets using a combination of eyes and ears!

All presets are just a starting point and almost always need tweaking to optimise their sound. This is doubly so for compressor presets because the creator/designer obviously has no idea of your source signal levels or time domain characteristics, so the threshold and release times -- at the very least -- will need adjustment every time.

...would I also be right in assuming that the ability to adjust "wet" and "dry" levels in their compression plug-in is basically parallel compression?

You would be right, yes!

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Re: Stuck in the Glue

Postby andrewsimper » Wed Aug 22, 2018 12:39 am

Thanks to everyone that has already helped out on this topic :thumbup:

In summary: The Glue is a feedback compressor. The Range knob controls roughly when compression stops. The Mix knob mixes the dry signal with the compressed, so if you did a plot of the ratio transfer shape it would be similar to the plot of the Range knob, but the section where compression occurs would be less horizontal (have a ratio more towards 1:1). The sonic result of the two methods is quite different, and the two methods can be combined.

Ratio transfer functions don't tell the whole story. The biggest problem is the knee area, which in The Glue is actually caused by the envelope follower and not the ratio shaper, and so it changes depending on the dynamics of the signal.

In the end just have a play and see what you like the sound of best in the context of the mix.

Please let me know if you have any further questions!
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Re: Stuck in the Glue

Postby varunbkk » Wed Aug 22, 2018 3:03 am

I think you're stuck because you've turned this into an academic exercise.
You need to experiment with audio and listen!

Forget about the Range function, leave it at default.

Put the comp on different parts of your mix and hear how the compressor reacts.
Use extreme settings to really hear the compressor working and then dial it back to more sensible levels.

On buses and sub groups experiment with extreme compression settings and then dialing back the mix knob to get a balance between maintaining original transients and a hyper-compressed sound.

Some starting points:

2-bus mix compression

Ratio - 4:1
Attack - 30 ms
Release - 0.1 s or use Auto
Threshold - Aim for 1 - 3 db of gain reduction and use makeup gain to match uncompressed vs compressed levels

The caveat is you need to put this compressor when you're just starting out a mix, and let it influence the compression, EQ and level decisions on each of your individual channels.
Don't just slap it on your 2-bus at the end.

Buses and sub groups

It works great for bass groups when you have different bass parts and you want to even out the levels between them.

Also works very well to add crunch and punch to your percussion bus.

Bass group - Medium attack, medium release, and 2:1 ratio with around 3-4 db of GR

Start experimenting!
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Re: Stuck in the Glue

Postby Hugh Robjohns » Wed Aug 22, 2018 9:50 am

EDIT -- apologies -- I thought I was responding to the Op, not the designer.. but I think the points still relate appropriately:

andrewsimper wrote:In summary: The Glue is a feedback compressor.

That's not what the block diagram in the manual shows. There it is drawn as a feed-forward compressor -- the side chain takes it's input from the input signal, not the output.

The Range knob controls roughly when compression stops.

Yes. It (would be expected to) control the maximum amount of gain reduction that can be applied.

if you did a plot of the ratio transfer shape it would be similar to the plot of the Range knob

Not really sure what you mean here. The parallel compression and range-limited compression transfer curves should look quite different (see below). But if you mean what happens when you blend in some dry signal to a range-restricted top-down compressor, it would indeed tend to straighten the curve out towards the linear 1:1 line. There wouldn't be much (if any) low-level lift because the amount of compression is inherently restricted!

Compression types.png


Normal compression (green) and limiting (light blue) pull the loud stuff down to reduce the dynamic range, whereas parallel compression (dark blue) lifts the low end to reduce the dynamic range (leaving transients largely intact). Range-restricted compression (orange) limits the maximum amount of gain reduction that can be applied, so results in an S-curve where the dynamic range is reduced, but only mid-level signals are really affected. The loud and quiet stuff is largely left alone, again leaving transients largely intact.

Of course -- I am talking entirely theoretically here, and haven't had the opportunity to use or test this compressor. Your implementation may well be different to my presumptions and expectations! :-)

In the end just have a play and see what you like the sound of best in the context of the mix.

Yep! I would never argue with that! ;-)
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Re: Stuck in the Glue

Postby desmond » Wed Aug 22, 2018 10:16 am

andrewsimper wrote:Thanks to everyone that has already helped out on this topic :thumbup:

Nice to have you here, Andy!

DSP rock star in the house! :clap:
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Re: Stuck in the Glue

Postby Martin Walker » Wed Aug 22, 2018 10:49 am

Indeed - welcome Andrew to the discussion, and to the SOS Forums! 8-)

There are some sticky arguments here, but you should be able to shed some truth on the proceedings, as you created the Glue to great acclaim ;)


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Re: Stuck in the Glue

Postby Gone To Lunch » Wed Aug 22, 2018 11:40 am

varunbkk wrote:I think you're stuck because you've turned this into an academic exercise.
You need to experiment with audio and listen!

No.

In my world curiosity about how something works under the bonnet is not an academic exercise at the expense of musical judgement.

I do in fact experiment and listen a great deal, which stimulates my curiosity all the more !

Forget about the Range function, leave it at default.

Certainly not !

See other contributions in this thread !

And, it doesn’t actually have a default as such, because different settings have different musical consequences - isn’t that the point of the control in the first place ?

Put the comp on different parts of your mix and hear how the compressor reacts.
Use extreme settings to really hear the compressor working and then dial it back to more sensible levels….

Indeed. This is why I want to understand in detail what the controls are actually doing to the signal.


The caveat is you need to put this compressor when you're just starting out a mix, and let it influence the compression, EQ and level decisions on each of your individual channels…

Don't just slap it on your 2-bus at the end.

Yes I did put it on the mix bus at the start of the mix, along with three other compressors I am studying. At the moment I am experimenting with mixing through the mix bus, because I have been reading Eddie Bazil’s ‘Mix Bus Strategies’. A rattling good read.

As I am mixing my own composition, the putative boundary between composition and mixing/mastering is something I seek to challenge for creative purposes - another reason why I want detail understanding. That is, to better inform my musical decisions.

Start experimenting!

As I have hopefully explained, I already do !
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