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VCA's?

Discussion in 'Sound, Music, and Intercom' started by Eboy87, Mar 15, 2006.

  1. Eboy87

    Eboy87 Well-Known Member

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    I know someone tried explaining this already, but, sadly, I still have no idea how these work. All I know is Variable Control Amplifiers, and even then, I'm a little iffy.

    Do they work in the same was as a group? Or are they more like a matrix?

    No pressing need to know, just curious. Thanks in advance.
     
  2. soundlight

    soundlight Well-Known Member

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    I thought it was Voltage Controlled Amplifiers...and I could use some clarification on them as well.

    Here's the Wiki: VCA's
     
  3. CURLS

    CURLS Member

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    haha nice end quote!

    Ok. here we go. this should be a fun one that i will attempt to explain and not get you lost in the process!
    First though kinda forget the whole matrix part that you mentioned.

    Ok so here we go on the subject of VCA's (Voltage Controlled Amplifier)
    First thing is VCA's do not pass any audio Whatsoever.! End of story.
    A VCA and a group are similair BUT NOT the same. Moving on.. a VCA is more or less a remote control for a channel or set of channels. (for bitechs kinda think a submaster.. sorta)
    So here we go scenario, lets start with a group first.
    So we'll say we have some female actors and some male actors and we want to group the male actors and the female actors into two seperate groups. When we assign them to a group respectively we know that when we bring up that group fader and then send it to the stereo bus if it's not already sent there it increases the amount of volume from the amount that you already have up on those channels.
    Now, here's where it can get tricky in similarities. If I have the first gurlz mic up and sent to the group as well I'm rockin and rollin. But, what happens if say for instance I take her channel and unassign her from the stereo mix but leave her group assignment up and turned on? Well, she's still there it is just decreased by a relative amount of dB. (10dB i believe) This is because she is being sent to a group bus and then that group bus is PASSING SIGNAL to the stereo bus solely(as well as its respective o/p's). Ok, now I made that point to say that some of us know tricks of using group inserts for this situation, some recording audiophiles mix this way, and that is where the two Merge and become similair.

    A VCA on the other hand is solely just a remote control for channel(s) on your board, as previously mentioned. So, back to our scenario we have the gurlz and the guys. Say for instance I take one of the gurlz and i assign her to my first VCA. (This is all assuming that some of us know proper gain structure and little beckys channel is at unity.) With her channel at unity and assigned to the first VCA and that VCA AT UNITY as well you should here no VOLTAGE gain difference like you would a group. Now, as you bring that VCA down you will hear her slowly go away(if you will think that as this the first VCA fader is being pulled down her channel strip fader is being pulled down at the same time and same voltage respectively and no its not literally moving with the vca this is just an example, moving fader VCA's those that know the D5 and digital consoles :)) As you bring the VCA back up to unity, then so does that channel become respectively. As well as if you go above unity, then that channel strip or strips are going above unity as well.

    Ok, so if your not totally lost. Lets recap! VCA's only remotely control voltage of fader(s) Whereas, groups pass voltage and and add voltage as channels are assigned. One of the big reasons that mix engineers prefer VCA's is it allows you to use groups for other things(i.e. go figure it out. lol) They allow you to control similair areas of your show (band, chorus mics, lavs., and so on) without having any voltage running through them, that's handy if the VCA section decides to take a dump.

    Ohh, and found a little furthur reading that may help, may make you get lost on the internet from AandH. http://www.allen-heath.com/US/ViewProductDownloads.asp?search=Mixing Live With VCAs

    Anyhow, I hope none of you got lost in this big ramble. If you have any questions don't hesitate to ask.
    Oh. and if any of you wonder y i say gurlz with a z it's because the performers use to be "CurlZ GurlZ" labled on the board. lol
     
    Last edited: Mar 15, 2006
  4. soundlight

    soundlight Well-Known Member

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    I didn't get lost at all...that clears it up for me, at least.
     
  5. RelativeMischief

    RelativeMischief Member

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    The summation of two identical waveforms is an increase of 3dB, just to clarify.

    Another thing about VCAs as well is to remember that you can't classify them as mono or stereo. They don't deal with audio signal, they're just a remote for voltage. Assign all the mono or stereo channels you want and you don't have to worry about pan or anything along those lines.

    For the math geeks: VCAs are a linear control, not logarithmic. As in, moving the fader 1cm is the same change in relative volume wherever the fader is, on the strip. Whereas with groups or channels, changing the fader 1cm is not as large a difference around unity, as it would be at the bottom of the strip, say around -50.
     
  6. Eboy87

    Eboy87 Well-Known Member

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    OK, I think I get it now. Would it be the same as saying it's like a fader on a light board? It sends an electrical to a dimmer, which actually does the work?

    And that pdf really helped. It's now safely tucked away in my show binder. Thanks CURLS.
     

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