Testing an SPL iron compressor - take a listen?

Picked up the PA Purple MC77 and the SPL Iron yesterday. Was experimenting with them today.

PA went to great lengths to explain why this thing was supposedly special. Basically what I concluded was that the Iron is super flat and transparent (meaning that it doesn’t hype any frequencies). But beyond that I was unable to tell it apart from any other super flat or transparent compressor.

I’m curious if anyone can hear a difference in the lead vocal on these. If you can’t that’s understandable, because at this point I’m questioning if the differences are pretty much lost on the listener anyway.

This is a UAD 1176. Not the PA. On my monitoring system, it seemed to hype sibilance and make a subtle spike in the midrange from 800 to 1.3k.

Here’s the Iron. Tell me if you think the sound difference is noticeable.

I like the first better, but I think it also sounds less compressed and less loud. The second feels louder, but not in a good way. The first feels like it fits in with the mix better, although it’s close enough that I’m not convinced I’d have the same opinion if I tested blind.

That’s cool. Much appreciated.

It was crazy how much detail was given in the documentation on whether the virtual transformer is set on the germanium vs the LED model etc… I can’t tell if that’s even making the slightest bit of difference, or every difference you and I heard here was completely based on how the thing was set.

My ears for this kind of stuff are pretty out of shape too. I haven’t done any serious music mixing in quite a while.

Hey Jonathan - It’s pretty subtle, but I think I prefer the second - it seems to be slightly warmer overall and have more solidity in the low mids and mids.

Do you use any PA stuff? *just curious.

No, I don’t think I had even heard of it before now.

hi I own the UA 1176 I used to use it on almost everything. I have since learned that I have no clue how it works. ha ha The truth.

I prefer the second clip. It was smoother with better clarity.

For most commonly run it 2 ways: either 4:1 or all buttons in.

4:1 - in front of (before) a slower compressor. For vocals attack at 5 o’clock and release about 2:00 then adjust from there, with anywhere from 3-8 db of GR. Then I start peeling back the attack and release times to manipulate sustain, grit, and smoothness.

All buttons in - for a hyped up smashing effect on a parallel drum bus or something that you just want to crush.


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They make a ton of different and unique plugins, their niche (in my opinion) is m/s processing and saturation emulation. They also have a nice library of hardware models.

@miked - don’t you use a lot of their stuff?

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Brainworx sells a lot of stuff on pluginalliance. I have a few of their freebies (bx_solo, bx_subfilter) and also their bx_opto (which is quite nice, though I don’t use it much since I got the Waves comp bundle).

Pretty decent plugins, IMHO.

I’m only listening on my MacBook Air. If I were on my monitors or Sennheisers I might feel different, but I’m with Andrew. The first one sounds thinner and crisper to me. The sibilance stands out more on the first one.

Actually, that’s probably a great way to check for sibilance and mid-range clarity.

@Jonathan - You can put me in the camp of “I’m not certain I hear the difference”. And yes, I’m lucky enough to have access to all of the PA plugins. But my go-to’s are the Vertigo VSC2 and the SPL De-Esser. I’ve played with the SPL Iron a little bit, but not enough to really have a solid opinion, other than it did a pretty decent job on the mix I was using it in. Lately, I find I’ve been gravitating towards the plugins that allow me to dial in things quickly and intuitively so I ca move on without too much hassle and not lose my train of thought.


the first one sounds better to me on the vocal. more clarity…exactly as you described it miniscule sibilance. the bass seemed less effected. it was odd the recording had dogs barking in the far background and a doorbell going off a few times but whose to judge art!

Prefer the first one (UAD 1176)- 8 out of 10 times in a blind test

After dissecting the mix, the first one has more spacial detail, there is a cleaner reverb on the vocal that seems to soften the mix in a good way for my ears.

On the second mix it seems that the spacial detail is lost to a certain extent(could be a preference thing).