How to test a compressor plugin ...

[bmanic]

I'm not saying that compressors that fail this test are useless. It's just that they are not perfectly transparent in a real digital audio sense. Yes, they might sound better - that's a seperate issue.

Which is why you should consider editing your original post. Calling this behaviour "harming" is rather bad choise of words. Let's consider this test on some true classics.

LA-2A - 'fails' the test
1176 - 'fails' the test
all analogue equipment in general - 'fails' the test

Are these harmful? I think not.

- bManic

[csl]

UAD Fairchild - Silent.

Which would indicate that UAD are not modelling the true behaviour of a fairchild correctly.. not even closely so then. Very disappointing indeed.

- bManic

Actually it fails the test. You'll hear a bassy signal left - as you should since the Fairchild actually rolls-off deep bass from anything passed through it. It's difficult to do this accurately as the FC output is not set at 0dB by default - the closest is one half-notch down from +2dB (with input and ratio set to min)

BobYordan - are you sure you're setting this up correctly?

[morelia]

Izotope Ozone, Classic Compressor, Buz GeneComp, GComp.

The only ones that pass a clear signal are kjaerhus and buz. What does it mean? I don't know.

[kylen]

The only ones that pass a clear signal are kjaerhus and buz. What does it mean? I don't know.

I think it just means that if you choose to test a compressor in this way and it doesn't null 100% then you're left with having to have an instance in both the "phase 0" and "phase 180" channels. The "idling noise" creates a somewhat arbitrary beginning point for you to try and deduce the exact sound the compressor adds. It gives you part of the picture at least. The good thing is once you start hearing it in some sort of isolation it becomes a little easier to hear what the compressor adds or subtracts from the overall sound. Then you can pick it out without having to do the null test if you like - like some of the folks seem to be doing here...

[atomota]

greendoor, 'doing harm' is not used correctly. Most compressors usually do what you are describing - working as a 'wire' when no compression takes place. But this means they do not work as they should in my quality standards. Every compressor should add 1st order DC filter since compression adds DC offest. This DC filter automatically removes 'wire' behaviour.

(I'm not taking sides here.) That certainly makes sense. A good DC filter would cause the output of this test to have near-DC frequencies. Any other output would have to be there for some other reason.

[bmanic]

Actually it fails the test. You'll hear a bassy signal left - as you should since the Fairchild actually rolls-off deep bass from anything passed through it. It's difficult to do this accurately as the FC output is not set at 0dB by default - the closest is one half-notch down from +2dB (with input and ratio set to min)

BobYordan - are you sure you're setting this up correctly?

Awesome! This is much more that I would expect. Very much inline with how the fairchild sample on the sintefex sounds. Maybe there is hope in UA after all!

Cheers!
bManic

[greendoor]

My choice of the word "harm" seems to be upsetting some people. I'm not saying that compressors that fail this test don't sound good! Just that the waveform is changed. Just like distortion can harm a waveform - but it might sound good.

If you can't cope with the word harm, just substitute it with a word you can cope with.

[greendoor]

Personally, I don't see the need to model quirks of analog hardware. I view compression, distortion, eq, phase shifting as seperate things. I would rather have control over these things seperately. I don't see the point in choosing a compressor plugin because it distorts or eq's the sound a particular way. I would rather choose my own distortion or eq.

[martian]

I'm not saying that compressors that fail this test are useless. It's just that they are not perfectly transparent in a real digital audio sense. Yes, they might sound better - that's a seperate issue.

how is it a separate issue? you clearly say in your op that compressors 'should' null with phase inverson and ones that dont are 'damaging' the audio.

yet you dont seem to understand why many processors wont null, you should have instead started the thread trying to understand the results of your new 'trick'.

[greendoor]

Sorry WM - you don't seem to understand what i'm talking about. I'm not actually taking sides - just that this is interesting information (to me) that helps me choose a compressor for a particular job. I understand perfectly WHY some compressors null and others don't. There are situations where you want phase accuracy between cloned tracks. It is very useful to know which compressor plugins will work in this situation or not.

I'm not opposed to "colorful" compressors - as I've been trying to say, that is a seperate issue.

[BobYordan]

UAD Fairchild - Silent.

Which would indicate that UAD are not modelling the true behaviour of a fairchild correctly.. not even closely so then. Very disappointing indeed.

- bManic

Actually it fails the test. You'll hear a bassy signal left - as you should since the Fairchild actually rolls-off deep bass from anything passed through it. It's difficult to do this accurately as the FC output is not set at 0dB by default - the closest is one half-notch down from +2dB (with input and ratio set to min)

BobYordan - are you sure you're setting this up correctly?

Hmmm, perhaps the audio file I used did not include enough bass elements??? Must check again, tomorrow.

[metamorphosis]

My choice of the word "harm" seems to be upsetting some people. I'm not saying that compressors that fail this test don't sound good! Just that the waveform is changed. Just like distortion can harm a waveform - but it might sound good.

If you can't cope with the word harm, just substitute it with a word you can cope with.

'Change' is a better word-
in the sense that you've used it, the only plugin that doesn't 'harm' an incoming signal is one that doesn't actually do anything at all....
m@

[Doug1]

greendoor, 'doing harm' is not used correctly. Most compressors usually do what you are describing - working as a 'wire' when no compression takes place. But this means they do not work as they should in my quality standards. Every compressor should add 1st order DC filter since compression adds DC offest. This DC filter automatically removes 'wire' behaviour.

You should try these tracks with analog and especially valve equipment - none work as 'wire'.

Please do not make wrong conclusions based on the fact discovered by greendoor. I regret he used word 'harm'. He should have used word 'adjustment' instead.

Very silly for someone to play around with some phase inverse and then jump on a forum to give his unjustified/uneducated results.
Claims such as what was said about Voxengo, can be damaging to companies.
You show professional restraint against these fools Aleksey, restraint that i could not, but i understand why you do so.
In conclusion, don't be fooled by these false accusations.

[kylen]

greendoor - somehow we have to account for harmonic distortion that naturally can occur when a transfer curve is modified like you mentioned earlier (in both analog & digital). It gets a little tricky in some of these compressors, take Kjaerhus GCO-1 for example. In classic mode you get harmonics only after you begin compression (after the transfer curve is modified in other words), but in opto mode the harmonic distortion pretty much goes away. Some of that distortion can result with attack/release setting too I expect but it seems a little less pleasant. Then you have the new Voxengo Marquis where there is harmonic distortion regardless of any compression settings but can be switched off. Then you have Voxengo Crunchessor which has harmonic distortion in parallel and can be fine tuned or turned off. For this reason I like to run a 1KHz tone thru new plugins so I can see what they're made of a little by looking at a spectrum analyzer for even and odd harmonics - even compressors! It makes me feels like I know a little bit about what's going on under the covers anyway - maybe explains a few things about the sound too.

PS: BTW everyone, I think greendoor has tried to explain that his use of the term "harm" is not intended as an insult. Unfortunately a loose interpretation in any language could lead to different conclusion - harm means change or modification to greendoor. To others it means something is ruined. In this case I think I would go with the term changed or modified personally which cover most any dsp operation.

[greendoor]

Thanks Kylen - I just wanted to draw attention to an idea that I found very interesting. It seems some people found this interesting, and others found it intimidating. Make up your own mind. If you don't understand this, don't worry.

If anyone wants to interpret this as an attack on anyone, I'm sorry you feel that way but you are wrong. I say what I think - this is a public forum and I don't have to protect or endorse any commercial product. I'm just interested in tools and techniques that help me make music.