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Logic Pro X Compressor Circuit Type Cheat Sheet

Holger Lagerfeldt

By Holger Lagerfeldt
in Tips and Tricks

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mkruse Newbie

mkruse

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Actually here's another question, will engaging the auto release give you two stages of release like an LA2A?

No, it won't.

 

*I am not affiliated with TDR in any way.

 

I'm curious, have you used TDR Kotelnikov?

 

http://www.tokyodawn.net/tdr-kotelnikov/ (there is also a paid version for a greater feature set)

 

It has an individual release control for Peak and RMS - the release of RMS section makes sure to keep the RMS long enough for low frequency events and short for higher frequency events - and includes control over the Peak Crest.

 

It's a very powerful compressor, too much for me to handle :)

 

From the User Guide -

 

Kotelnikov uses an elaborate control system based on two specialized parallel paths, each handling specific

signal phases independently with high technical effectivity and musical grace. The compressor runs two distinct

and separate detection and compression algorithms in parallel:

 

A. Peak Path

The peak detection/compression path primarily follows the rectified version of the (true!) audio

waveform with great precision. The peak path’s release phase can be tuned via the PEAK RELEASE

control, but also automatically accelerates the release time in certain, high dynamic range situations.

This avoids over-compression of small, “crispy” transient events. This form of over-compression is

highly audible, as it dulls the original signal substantially and can creates a “nervous” pumping sideeffect.

 

B. RMS Path

The RMS path reacts to overall energy levels (similar to human hearing) and ignores short transients. It

can be seen as a very slow and smooth compressor that handles the constant or ‘steady-state’ parts of

the signal. To be honest, Kotelnikov’s RMS path doesn’t use a true RMS detection in the “text-book”

sense. Instead, it relies on a highly advanced derivate of the regular RMS detector based on a precise

Hilbert Transform detector. The result is a frequency-independent RMS detector, practically free of

any harmonic distortion. Contrary to conventional RMS detectors which handle low frequencies much

like peak detectors and only higher frequencies as true RMS, Kotelnikov’s RMS stage automatically

uses the optimal RMS window size for every frequency. Additionally, Kotelnikov’s RMS path features

an advanced release gating (“freezing”) mechanism preventing noise floor build-ups during

programme pauses as well as other forms of pumping. It activates as soon the RMS section detects a

sudden pause in the input signal.

 

To summarize, in contrast to the peak stage, the RMS stage’s own dynamic behavior has the ability to

lengthen the RMS release time as required by given audio content. Kotelnikov can even increase RMS

release to (almost) infinity during certain situations.

 

The section generating the highest reduction at a specific point in time takes control of the whole compression

action. Technically speaking, we have 2 cross-linked side-chains running in parallel, whereby the peak section

mostly controls short, high amplitude events and the RMS section takes control over sections having “steady

state dynamics”. This contradiction is perhaps better explained as “Sections without substantial dynamics”.

This unique approach offers all of the advantages of peak compression combined with all of the advantages of

RMS compression. Furthermore, the RMS path negates the disadvantages of the peak path and vice versa. This

design guarantees a very stable stereo image and low compression artifacts over a wide range of material and

settings.

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Holger Lagerfeldt Collaborator

Holger Lagerfeldt

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In the PDF you'll see "Range" mentioned twice:

 

"Range: Max. gain reduction (cap)"

 

So a range parameter allows you set the maximum amount of gain reduction regardless of what the compressor actually wants to do.

 

If range is user adjustable it means you could set a low threshold and a high ratio and your compressor could be doing between e.g. 0 and -10 dB of gain reduction on a track for examlpe. If you then set the range parameter to 6 dB it caps the gain reduction at -6 dB. On anything between 0 and -6 dB of GR the compressor will act exactly like it did before, but it won't reduce more than -6 dB when it would otherwise have done so.

 

In practical terms this means you have more freedom in setting your threshold and ratio because you can avoid over-compression on certain loud peaks, that would otherwise have forced you to generally lower your ratio or raise your threshold for that track.

 

Example:

You use a compressor on a piano and you're on getting between -3 dB and -6 dB of gain reduction on the piano on average. You're very happy with the sound and your settings and you don't want to change them. Then suddenly in the C-part of the song the piano becomes a bit more aggressive and louder and this causes the compressor to do too much gain reduction, e.g. -10 dB of gain reduction on certain peaks. The piano sounded great at -6 dB of gain reduction, but not at -10 dB, but this is only a problem in the C-part. If you automate the ratio you could avoid this problem (although you would change the sound), but if these peaks happen sporadically throughout the song it could be a real P.I.T.A. to automate. Instead you can simply reach for the range parameter and set it to 6 dB. Now you have exactly the same sound as before, but when the C-part or aggressive parts kick in, the compressor doesn't gain reduce beyond -6 dB. You can keep your settings and the sound you like and the problem is solved with just a single parameter.

 

Flux Solera and FabFilter Pro-C 2 are examples of compressors with user adjustable range.

 

In the case of the Logic Compressor it's not user adjustable, each compressor has a built-in range (see the PDF) that far exceeds how much compression you need in most cases.

 

However, the range could vary with ratio. So not only does amount of compression depend on the threshold and ratio settings (and attack and release of course), but it could be capped depending on the ratio setting. This is a hidden parameter that's intrinsic to each model.

 

This is called "Ratio dependent range: If range varies with ratio" in the PDF. Looking at the PDF you'll see different models have different ways of dealing with that, but generally it means that lower ratios will have some kind of related gain reduction cap. Not in all models though, as you'll see in the PDF.

 

Many compressors have this hidden ratio dependent range built in, e.g. Waves Renaissance Compressor and many emulations.

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mkruse Newbie

mkruse

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What are people's thoughts on Logic's SSL emulation? Does it accurately capture the colour, and the talked about ability to 'glue'? Or does it simply emulate the response to dynamics? I'm trying Largerfeldt's free presets (thank you) but I do not have another SSL type compressor to compare it too, except for the free Acustica Audio Tan Compressor, which is supposedly based around an SSL Bus, but it is not a clone. It has much more colour than Logic's Vintage VCA.
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AMD Collaborator

AMD

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What a brilliant thread! Does anyone have a copy of Lagerfeldt's Logic Pro X Compressor Circuit Type Cheat Sheet? The original link doesn't seem to be working.

Thank you for pointing that out. I just attached the PDF to the original post in this topic.

 

Brilliant! Thanks David. And thank you Lagerfeldt for taking the time and effort to create and share the cheat sheet.

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AMD Collaborator

AMD

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You're welcome, and definitely, big thanks to Lagerfeldt for providing that. Also make sure you read the topic he linked to in the original post, unfortunately the images are missing but still lots of good information there.

 

Will do, thanks David.

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AMD Collaborator

AMD

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Hi everyone. Throughout this thread lagerfeldt mentions some updates to the chart, which aren't included in the one I downloaded from his first post in the thread. The updates mentioned are the addition of a "Hidden frequency dependency" parameter, aka. "if bass frequencies can result in more compression" and "Ratio dependent range" information.

 

I was wondering if anyone has an updated one they wouldn't mind uploading?

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Zipfunk Rising Star

Zipfunk

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Hi everyone. Throughout this thread lagerfeldt mentions some updates to the chart, which aren't included in the one I downloaded from his first post in the thread. The updates mentioned are the addition of a "Hidden frequency dependency" parameter, aka. "if bass frequencies can result in more compression" and "Ratio dependent range" information.

 

I was wondering if anyone has an updated one they wouldn't mind uploading?

 

I second this

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