QuPac Gain Staging

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This topic contains 3 replies, has 3 voices, and was last updated by Profile photo of Jun Jun 5 years, 1 month ago.

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  • #55122
    Profile photo of Jun
    Jun
    Participant

    Hi Guys,

    I am new to QuPac from Presonus Studio Live.
    As a standard, I usually set the input channels to unity then increase the gain gradually before feedback.
    I’m just wondering if there is a difference in QuPac or there is a better way achieving optimum gain structure in QuPAC.

    Thanks do much in advance for any advice you can provide.

    Jun

    #55128
    Profile photo of GCumbee
    GCumbee
    Participant

    Pretty much like on any console. You want the gain set to where the fader operates best in that upper 1/3 area. More range below than above. So a good method is put the fader at the zero or shaded area then adjust your gain to where it needs to be. This varies with input source. Different mics, instruments will have different levels. Idea is just to keep the faders at a good point to operate. Of course you have to make sure you’re not overloading either. You see a channel clipping then lower the gain not the fader. Then re adjust fader to suit.

    #55134
    Profile photo of cornelius78
    cornelius78
    Participant

    Not using a Qu-pac, but my procedure is pretty much the same for all mixers, be they analogue or digital.

    I tend start with the amps and channel gains turned right down, get a “performance level” signal into a channel, PFL it to get it on the higher-resolution meters, and raise the preamp gain until I’m hitting the input at about -18dbFS (which on A&H digital consoles is at about the “0” mark; they’re making it easy to transition from analogue in that respect.) Depending on where in the signal chain the console meters from, you might need to make sure you have all channel processing switched out. If using an analogue console, I aim to have the signal dancing around the “0” mark.

    I then raise the channel fader and main output fader to unity. Then, with signal still coming through, I slowly adjust the input sensitivity on the FOH amp (or active speakers) until the sound is comfortably loud enough in the room. I do a similar thing for stage monitors: once the preamp gain is set, I raise the channel>mix send fader(s) + mix master fader(s) to unity, then adjust the stage monitor amp(s) until the signal is loud enough on stage from the monitors.

    If when using this method I find I’m having to turn the amps up into distortion, then I’d consider it a case of “not-enough-rig-for-the-gig.” If this method generates feedback and I can’t\don’t want to change the mic\speaker placements and mic choices I start notching it out with the peqs.

    On the QU series there’s a trim that can be engaged on the DOs if the signal is the wrong level for Qu-Drive or ME1s.

    This method allows me to mix performance-level signals with my faders around unity (for both FOH and monitors,) get a good SNR for the preamps, and have a decent amount of headroom (18dB) for big transients before clipping the ADCs. If during the gig I need to get louder I’ve got 10dB of headroom on the channel faders, 10dB of headroom on the master fader, (same with the mix send + mix master faders,) and potentially up to another 10dB of headroom per DCA master (+10dB if I route the signal through a subgroup,) before I need to adjust the preamp (which would affect any other console sharing the preamps, eg a FOH\monitor split, or a recording feed) or the amps (which may be in-accessible from the mix position.)

    One good thing about doing it this way is that if you know that -18dBFS is the level you’re aiming for on your inputs, you don’t have to wait for the band to get there to set the amp sensitivities. You can do it with any input source you want (eg a CD,) as long as you dial it up such that (the loud parts of) the source is hitting -18dBFS, and you raise its channel fader and output fader to unity. Later when the band does turn up, as long as you dial their preamps up such that their “performance-level” signals are also all dancing around -18dBFS (“0” on A&H digital mixers,) when your raise their channel faders to unity (and you keep the master output fader at unity) they’ll all be a similar, comfortably loud level in FOH. You can then massage your channel faders to get the mix you want.

    A variation to this method would be on consoles which have preamps that “soft clip” nicely (Midas.) They often have a preamp gain then a digital trim. In this case I’d start with the preamp gain all the way down and the digital trim at unity, dial up the preamp towards saturation until I hear the “soft clipping” sound, then use the channel’s digital trim to maintain the preamp’s sound but bring the signal level down toward -18dBFS. Once at -18dBFS, faders to unity and adjust amp’s sensitivity to suit the room.

    I know some people will wind the amps all the way up, faders to unity, then need to have the preamp gains quite low to keep a comfortable level in FOH. Although using this sort of gain structure can result with the same SPL in FOH as the method I detailed above, it means the signal’s SNR isn’t as good, and you’re not making the most of the preamp. It also means any noise (eg hiss) in the system will be amplified a lot, as the amp’s sensitivity is so high. In a quiet room this sort of gain structure often results in a lot of hiss. This is especially noticeable in a HOW setting: the hiss might not be as noticeable when the band is playing, but later on during the service when there’s only one open mic (eg the preacher) and the amps are still wound all the way up, the noise in the system becomes a lot more noticeable.

    #55138
    Profile photo of Jun
    Jun
    Participant

    Thank you so much GCumbee & Cornelius.😊

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