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VCA Compression, The SSL G Bus & Dbx 160? Dynamics Processors (HW)
Old 14th December 2018
  #1
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Davster's Avatar
 

VCA Compression, The SSL G Bus & Dbx 160?

Hi Slutz,

First thread start from me. Love this forum, so much to learn from so many great people!

_____

So, I was recently (finally) digging into exactly how each compressor type works in terms of physics, when to use the different types, the characteristics of each type etc.

VCA compressors are often termed to be pretty transparent, with very fast attacks. They're the option to choose when taming peaks, and aren't particularly suitable for macro dynamics. That all makes makes sense to me, but what made me scratch my head was seeing that the SSL Channel & Bus compressors are VCA, as well as the popular Dbx 160.

People always talk about the SSL G Bus compressor as adding 'glue', 'smoothing a track together' and other such imprecise terms. People say they 'love the sound' of the G bus, and it goes on mix buses all over the shop. The Dbx 160 appears to be popular for drum busses, especially when you're not after a clean sound (?).

Does this not go against what a VCA compressor *should* do? Transparently control peaks?

What, specifically and technically speaking, makes the SSL G Bus and the Dbx different from this theoretical 'ideal'? Am I just missing something about how VCA compressors work? When people say they love the 'sound' of the G bus and the colour it brings, are they just talking out their ass?

____

Thanks so much,

Dave
________________
Old 14th December 2018
  #2
Quote:
When people say they love the 'sound' of the G bus and the colour it brings, are they just talking out their ass?
I think so. I roll my eyes when ever someone says "it colors the track"
Most cheaper rack compressors are controlled by VCA. So clean and transparent are not what you think of when it comes to cheap hardware compressors. Its actually the opposite.

As far as the DBX, I would keep that thing far way from any bus or track insert. As far as being popular, I do no think they are.
But if you like the sound of it, its all good. We all have different preferences and needs when it comes to sound and sound design. We use what ever we need to use. if that means you need to use the DBX to get it, then that is the best tool for the job.
Old 14th December 2018
  #3
To me, best way to understand those issues is to learn how to listen to compressors. Bus compressors are also known for their abilities to shape the sound stage of a mix beautifully. DBX 160 is to me more aggressive and not that great for that "glue" thing. If you listen to SSL comp carefully, it puts kick and snare in a particular place in the mix that sound like "record." - for especially rock genres. Also it shapes transients of kick and snare, lengthen their tails, and brings the ambients of a mix, again very particular and beautiful way.
Old 14th December 2018
  #4
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Davster's Avatar
 

Thanks for the replies guys. So can anyone explain to me, specifically in physics terms, the actual difference between the DBX and the SSL then...? They're both Voltage Controlled Amps, so I'd have thought there can't be that much difference in how they're actually working.

Why is one more aggressive and one not...? Isn't that just down to the user and the controls, since they work on the same electrical principles? FET compressors start to really impart character, whereas VCAs should be more transparent... right?

Looking for a precise physics explanation for it really.

I know that the SSL G Bus is a feed-back style compressor, but the DBX is a feed-forwards. Maybe that's part of the difference?
Old 19th December 2018
  #5
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BIG BUDDHA's Avatar
i own both.

the difference is how you use them.

the ssl comp usually runs 1 or 2 db of gain reduction, and for me personally i run slow attack (15 to 30 milliseconds) and fast release (100 to 200 milliseconds) on 2 buss

so its just keeping things under control a little.

the DBX 160-s i use for drums. live drums, kick and snare.

and if you could find a drummer who could play with 1 or 2 db of dynamics, then that would be a miracle.

so the DBX works much harder, sometimes 4 to 6 db of gain reduction, faster attack and release to suit song tempo.

also the DBX has a hard knee or soft knee setting which my SSL comp does not.

to simplify the DBX is squashing large dynamics, and the SSL is smoothing gentle dynamics.

also its usual to sidechain the SSL, but the dbx is processing full bandwidth.

so they are technically and sonically different devices, which people have discovered work well in certain audio locations.

hope that helps. Buddha
Old 19th December 2018
  #6
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you might want to forget your general assumptions about compressor types/designs.
VCA's are not clean per se, (think all old DBX's) not all FET's impart a lot of color.(like the Daking FET II or III)

and yes, feed forward and feed backwards type VCA's can sound drastically different.
this becomes very evident once you have had a VCA on hand that can do both.
Old 19th December 2018
  #7
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Perhaps people are looking at this from the wrong Angle as it’s not that :-> All VCA’s are Equal <-: sure euphony to sheen, to hair to insert you favourite description on SSL type compression is used! Though look in any professional studio I doubt you’d see a SSL Stam knock-off seriously hanging off the console!

When you’re talking about SSL Bus Compression you’re hearing and feeling Ultra Fast VCA technology and under to overshooting the waveforms or side chain multing as an insert on the Bus out to get a certain sound, THAT VCA’s series chips new model dependant, have a much faster tolerance and Faster near undetectable to ear slew rate. So here you’d possibly say Old Black to Gold can DBX 160 canned VCA technology slew rates 30 plus years old actually are two very different beasts!

Both the Dynamic Range alongside the Signal to Noise Ratio and the slew rate of the Voltage Controled Amplifiers VCA’s are very different in both units different. So are the valid, Circurty and the specifications of the headroom and ultimate level in rate if onset in compression. Something like the Smart C2 or SSL XLogic, in Analog terms is near 20 bits if you converted it digitally and so to the DBX 160 which perhaps might be described as 14 bit PCM Sony Encoding F1 style!

Sure people use descriptive words and phrases, though if V51 Neve EQ’s add Colour or warmth that too, might indeed be valid, I’d be wondering if a Stam or Warm Audio Neve added warmth ass talk! Then again just my opinion?

Ho hum?
Old 19th December 2018
  #8
Quote:
to simplify the DBX is squashing large dynamics, and the SSL is smoothing gentle dynamics.
that's a good sum up.
the DBX also has a ratio function that far exceeds the SSL.

generally speaking i use my 160 for tracking and sub grouping whereas the ssl
is a little more subtle for a whole mix.
i wouldn't say that the ssl is aggressive like the 160 can be but that could be just down to the timing constants which in the 160 seem to be set fairly fast.
Old 19th December 2018
  #9
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jdier's Avatar
 

I think the overall design of the circuit has more to do with the resulting sound than the mechanism for peak reduction.

Much like a D112 and a Senn441 are both dynamic mics, they sound dramatically different.

Or a Cadillac and a Lamborgini are both cars, but they excel at different things.
Old 19th December 2018
  #10
...there are different VCA circuits, and the circuitry surrounding the gain reduction elements is different also...you can broadly group VCA compressors but not much more than that...a DBX 160 VU is substantially different to a SSL Bus compressor in sound...it's just because of the real world implementation which differs from the theoretical basics...
Worth noting that a SSL Bus comp is not coloured (although some do give a very minor colour to the signal)...they are mostly used as described above on the mix bus for 1-2db of gain reduction on the master which subtly helps glue and add some bounce to the mix...sometimes people use them to thwack the drum bus also...
Old 19th December 2018
  #11
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Quote:
Originally Posted by Norman Lindsey View Post
that's a good sum up.
the DBX also has a ratio function that far exceeds the SSL.

generally speaking i use my 160 for tracking and sub grouping whereas the ssl
is a little more subtle for a whole mix.
i wouldn't say that the ssl is aggressive like the 160 can be but that could be just down to the timing constants which in the 160 seem to be set fairly fast.
Maybe you’d drop a pair of 160’s into an 1972 MCI 428 Console, though on anything modern those 160’s might crunch the signal programme captured too much! The reason I personally feel it pointless in buying TX modded SSL VCA compression as really, you want it invisible to a degree just tightening up Busses on a Console making certain balance and image intact tightly remains! Maybe that’s why it’s gently or smacking Bum settings? Very different on an SL4000 I can say that.

Timing constants on the C1LA are incredibly flexible maybe also hard to understand for some? Thus 2-3dB set and forget ratios on SSL! The older GFX 384 claimed to have much more grunt? Hmmm? Still... place for everything and those 160’s when overhauled can add that certain vibe, can’t deny that!
Old 19th December 2018
  #12
Gear Nut
 

Quote:
Originally Posted by TheLastByte View Post
Perhaps people are looking at this from the wrong Angle as it’s not that :-> All VCA’s are Equal <-: sure euphony to sheen, to hair to insert you favourite description on SSL type compression is used! Though look in any professional studio I doubt you’d see a SSL Stam knock-off seriously hanging off the console!

When you’re talking about SSL Bus Compression you’re hearing and feeling Ultra Fast VCA technology and under to overshooting the waveforms or side chain multing as an insert on the Bus out to get a certain sound, THAT VCA’s series chips new model dependant, have a much faster tolerance and Faster near undetectable to ear slew rate. So here you’d possibly say Old Black to Gold can DBX 160 canned VCA technology slew rates 30 plus years old actually are two very different beasts!

Both the Dynamic Range alongside the Signal to Noise Ratio and the slew rate of the Voltage Controled Amplifiers VCA’s are very different in both units different. So are the valid, Circurty and the specifications of the headroom and ultimate level in rate if onset in compression. Something like the Smart C2 or SSL XLogic, in Analog terms is near 20 bits if you converted it digitally and so to the DBX 160 which perhaps might be described as 14 bit PCM Sony Encoding F1 style!

Sure people use descriptive words and phrases, though if V51 Neve EQ’s add Colour or warmth that too, might indeed be valid, I’d be wondering if a Stam or Warm Audio Neve added warmth ass talk! Then again just my opinion?

Ho hum?
You’re right about different VCA chips effecting the sound dramatically. Simply put, it’s wrong to assume two compressors will sound similarly just because they use the same mechanism, be it VCA, option, fet, vari-mu, or anything else. Not sure why your post turned into a criticism of certain clone manufacturers. I’ve never used a Warm personally, but I can say that Stam gear, especially the SA-4000 sounds awesome and is built very well, and yes I’ve used the bus comp on an actual SSL.
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