difference between VCA and Optical compression

Discussion in 'Tracking / Mixing / Editing' started by J-MADD, Dec 16, 2004.

  1. J-MADD

    J-MADD Active Member

    I dont really understand the mechanical (and thus sonic) differences between these 2 types of compressors. I am starting to look into vocal compression and I am trying to understand the science behind compressors.
  2. JeffreyMajeau

    JeffreyMajeau Active Member

    VCA = voltage controlled amplifier. It analyzes the incoming signal and when the power of the incoming audio exceeds the threshold, it turns the output down.

    Optical compression uses (usually) an electroluminescent panel and a light detecting resistor. The more light, the less resistance, the more compression.

    VCA is typically "harder", optical is typically "smooth".
  3. J-MADD

    J-MADD Active Member

    Thanks for the explaination. So If I was looking for a heavier vocal compression, typically a VCA would be more suitable?
  4. Kurt Foster

    Kurt Foster Distinguished Member

    Actually, the opposite ... because the optical compressor (El OP) is smoother and gentler, you can pull more gain from a signal without audible artifacts. If you want the compressor to pump and wheeze, adding the sound of a cheap stomp box type of compressor, then a vca comp is what you want ... for the most part vca comps are relatively inexpensive except for a few like the Distressor that are IMO more hype than good ...
  5. JeffreyMajeau

    JeffreyMajeau Active Member

    Well, it sorta depends what you're looking for. VCA compression can stomp the $*^t out of stuff, but IMHO makes stuff sound pretty small while doing so.

    Optical compressors usually sound a lot bigger at the same or even more gain reduction.

    My dbx 163x's can smoosh things with all get out, but they don't sound big when you are doing that.
  6. claude

    claude Guest

    Kurt, AudioGafWhat's your thoughts on the CraneSong Trakker

    Kurt, AudioGaff, what are your thoughts on the Cranesong Trakker?
  7. midiwhale

    midiwhale Guest

    AFAIK technically the difference is in the gain transfer characteristic I think it's called hysteresis isn't it?
    Or putting it another way, the linearity and slew (response time) of the level change vs control voltage.
    Also I believe LDRs have a much narrower threshold of activity (dynamic range).

    If you look at the response curve of an LDR in the RS catalogue you'll see what I mean.

    Semiconductor based VCA's tend to be more linear (unless designed deliberately otherwise) whereas optical elements tend to exhibit a more drunken S curved response.

    You could visualise it slightly like tape saturation perhaps.... although that is a bad analogy.
    But remember that it is in context of it being used in the gain reduction element and not just as a pass through amplifer.

    Personally I think it's more important how the detection circuit is configured. You can make a VCA style element behave in almost any way - including an optical transferance.

    I've never found an optical that I liked the sound of. But that's just my opinion.

    But I have found an incredible array of characters and textures in different semiconductor based VCA compressors though.
    You wouldn't believe how wildy different alternative compresors can sound - but hopefuly you do ;-)

  8. anonymous

    anonymous Guests

    Oh goody... I love "generalities"... they're so stereotypical.

    There are all kinds of different "voltage controlled amplifier" designs, some good, some bad, some great, some made by dbx, some that are "class A/discrete" some that have great control circuitry operating them and some that have shitty control circuitry operating them.

    There are all kinds of different optical designs... some good, some bad, some fast, some slow... some that are very consistent and some that are rather inconsistent...

    The bottom line being that EACH design should be evaluated on it's own merit for different applicaitons.

    One of the "fastest" compressors I've ever used is the Pendulum Audio OCL-2 [it doesn't necessarily have to be set up to be fast, but it can be set up that way], which uses an "opto-attenuator" as it's gain reduction cell... one of the "smoothest" compressors I've ever used is the Crane Song LTD. "Trakker" which is a "VCA" based unit...

    Just as there is more to a car than the engine... there is more to a compressor than just the gain reduction cell.
  9. JeffreyMajeau

    JeffreyMajeau Active Member

    So, as usual, I'm full of sh*t.
  10. Kurt Foster

    Kurt Foster Distinguished Member

    I'll still take my Urei 1178, LA4s and my Manley El Op over a Distressor, any day regardless of how they work. As is mentioned often, YMMV so listen for yourself ... I'm pretty sure if you have the chance to compare, you will end up hearing what I hear ... Of course, I'm full of sh*t too .... and I don't sell gear ...
  11. JeffreyMajeau

    JeffreyMajeau Active Member

    I wasn't trying to flame Fletcher, just sorta pointing out how his experience and comments were spot-on, but I managed to make myself look like an asshole.

    I have nothing but respect for Fletcher and his opinions. He knows what he's talking about and his stuff sounds *great*.
  12. Kurt Foster

    Kurt Foster Distinguished Member

    well Dan, I don't think you are full of sh*t ... so there!
  13. buzz

    buzz Guest

    WOW maybe we should put a little compression on this thread ???

    wadda ya think VCA or Optical ????????????? maybe some subatomic particle compression !!!!

  14. JeffreyMajeau

    JeffreyMajeau Active Member

    Well, let me clarify my generalities a bit:

    It's been my experience (far limited compared to Fletcher and others on the forum) that VCA compression is a little harder edged, or "forward" sounding than optical units.

    I think if you're looking for heavy compression, you can get that with any compressor, even a 3630. I have experienced this time and time again - no single piece of equipment is going to always be a "home run" unit. If all you have is a cheap, nasty box, well you'll learn how to get the results you want from it. Engineering well is NOT about patching in buttloads of equipment. Engineering well is being able to solve problems and achieve the desired sonic results regardless of the tools at hand.

    Not everyone used to have compressors, EQs, etc in unlimited quantities. Engineers used to ride gain to tape, ride faders to even out vocal performances, choose microphones based on their frequency characteristics instead of using EQ, etc. to get the best results. Most of the recordings I absolutely love were made 20+ years before I was born. Learning the techniques of the past, before this glut of equipment, is a good idea.

    Now that I've ranted how things ain't what they used to be (like I know what the hell I'm talking about)...

    J-MADD, what're you looking for, exactly?
  15. J-MADD

    J-MADD Active Member

    Well, since I've never used any great compressors on vocals, I don't know what makes a compressor sound great. What I like about my crappy little marshall kick pedal compressor is that it puts the vocals right up in your face. I like the way the breath sounds are pulled right in there as well. When I sing heavier songs I generally get right in the grill of the mic, kinda like the deftones. Ussually I can get this to sound fine when I sing the softer passages, but when its time to belt out I need it to not crap out. The RNC craps out when I get to heavy parts in a song and the Marshall does not. If anyone has listened to the song Change (in the house of Flies) from the deftones, you know the sound I am talking about. There are so many albums out there where singers go from a whisper to a yell without distorting. I just want that.
  16. Screws

    Screws Active Member

    I thought the Trakker used an FET gain element.
  17. Daweenis

    Daweenis Guest

    Here's an extremely informative article explaining the different types of compression, uses and even some eclectic model choices if you're in the market.


    It's a few years old but it's an excellent resource for a comprehensive overview of Compression...

    Good Luck !!
  18. JeffreyMajeau

    JeffreyMajeau Active Member

    Singing right up against the grille of the mic in the studio isn't what I'd consider the best mic technique. I guess it'd be okay if you're using something like a 57/58 and trying to duplicate what you'd do in a live performance.

    If you're using a condenser, singing that close to the mic is going to give you loads of proximity effect, which'll make everything muddy. Back off a bit, and then for the louder stuff, back off even more. Search some of the audio forums for "mic technique" for some tips.

    Also, check your gain staging - RNC is a really great compressor, if it's having trouble with louder sections, perhaps it's input is being overloaded.

    If you're whispering and then screaming in the same song, you may want to think about tracking the whisper stuff on one track with it's own settings and the screaming stuff to a different track with different settings, optimizing for both that way.

    Trying to do it all in one pass may be the root of your frustration.

    The sound you're describing is a very hyper compressed sound that you can get from a lot of stuff. An L1 plugin or a Maxim plugin will give you what you're looking for. Pull the threshold slider all the way down and then adjust the output so that you're right around whatver your 0VU is.

    In hardware, you'll just have to play with it. Adjust your ratio so that it's high, 10:1 or more. I'd set the threshold so that everything is being compressed, even the whispers. Probably medium attack with a long release to keep things smooth.

    It's impossible to give exact settings via the web.

    One thing you may want to do is put a low cut on your mic pre, especially if you're singing that close to the mic. All that low end will absolutely torture the compressor. If not before it, then definitely after.
  19. J-MADD

    J-MADD Active Member

    Yes, I always put a low cut filter on my voice. There are songs If I am singing to say an acoustic guitar track, where I can back off the compressor and the mic, but once again if I try this with a harder rock song (something like tool, deftones etc) it sounds wimpy.
    With regards to overloading the input on the RNC, I have got the 428 preamp turned down as low as it will go. I mean when I am singing I am not even moving the VU meter.
    Thanks to everyone for their help with this issue. I think my next move might be to start looking at a Manley El OP. I have been reading good things about them. I just hope that my preamp will not overload that compressor as well.

  20. JeffreyMajeau

    JeffreyMajeau Active Member

    What's your gain staging and your connections?

    I.E. great, you've got the input down low, so, do you have the output cranked? How are you patching into the compressor? Are you feeding a -10 box with a +4 signal?

    Throwing gear at a problem never really fixes it...

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