VCA fader gain

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This topic contains 2 replies, has 2 voices, and was last updated by Profile photo of FitzroyChris FitzroyChris 11 months ago.

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    Profile photo of FitzroyChris

    When a fader channel is assigned to be a VCA controller over 1 or more channels which feed the L/R output, is the unity gain position of the VCA right at the top (i.e. +10dB marking) or at the nominal 0dB marking (meaning that at full up you should get an additional 10dB gain).
    I’m getting some strange lower level effects using such a VCA where the channels also feed an additional mix group; maybe I need to put some tone through and monitor the different levels through the system…

    Profile photo of KeithJ A&H
    KeithJ A&H


    Apologies in advance if you’re already aware of most of this –
    The DCA 0dB point matches the fader markings and works alongside the main channel fader – you can also think of it as working on the main channel fader. DCA’s are sometimes described as a remote control for channel faders, but as both the channel and DCA fader positions are acting on the same signal at the same time, both matter so this can be a confusing description.

    The total main LR send level of any channel which is a member of a DCA, is the individual channel fader position plus the DCA fader level.
    So if, say, you have the main LR channel fader at +5dB and the DCA fader at -5dB, the actual send level to LR would be 0dB.
    Or, if the send level to the main LR from the channel was at -30dB and the DCA was right up at +10dB, then the send level to the main LR would actually be -20dB.
    Because the DCA acts on the main fader/level of the channel, it will also affect all post-fade send levels from that channel.
    As the faders have an audio taper (with more resolution around 0dB), it can be tricky to visualise what’s going on with the actual send level, because it’s not simply a case of averaging the two fader positions.

    A channel could also be a member of multiple DCA’s! In which case, the actual main LR send level = main LR fader + DCA fader 1 + DCA fader 2 + DCA fader 3 etc…

    If none of this explains what you’re seeing/hearing, could you try to describe the strange effects you mention?
    Perhaps also with some detail on the assignments (or not) to LR, Group and DCA from the input channels.


    Profile photo of FitzroyChris

    Keith – thanks for the comprehensive reply. I just wanted to check that you can get +10 dB gain with a VCA fader full up, which I checked this weekend.
    The ‘weird effect’ that I mentioned before was due to an audience mic part-cancelling out a particular channel when faded up – it just happened to be attached to a VCA group, but this wasn’t the cause. When I switched the phase of the audience mic it improved the situation significantly…

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