Gain vs trim

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This topic contains 9 replies, has 7 voices, and was last updated by Profile photo of Chris93 Chris93 8 years, 6 months ago.

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  • #23364
    Profile photo of Ron
    Ron
    Participant

    We just installed our new GLD-80 and are amazed at the improvement in our sound in the room. However, until a new users manual comes out that has more detail, we have some basic questions about how to optimize the gain structure in the system.

    Our old Mackie board had one trim knob at the board entry point. The GLD has a gain level you can set at the preamps and a separate trim level you can set at the surface. This seems to provide access to two points of gain/trim. It would be very helpful to understand why there are two and what role each one plays in the signal flow into the board.

    Could someone advise me on the proper procedure to ensure we have the best possible gain available? For example, should I zero out the TRIM at the surface, set the best GAIN at the preamps in the digital snake to allow the faders to ride at unity? And once I do that, what would I use the trim control for? We are sending channel and Aux submix feeds to our Aviom system. Will changing the trim affect the send level to the Avioms like the gain control does?

    Thanks for any suggestions or recommendations. I long for a much more in depth owners manual that can address these kinds of questions.

    Ron

    #31755
    Profile photo of clarocque
    clarocque
    Participant

    Ron,

    I use the trims when doing a digital split and sharing pre-amps.

    This can be when using I/O card to another mixer or if you simply want to route same pre to 2 different channels. Like if you want separate channel for monitors.

    Example:
    Pres 1-24 -> channels 1-24
    Pres 1-24 -> channels 24-48

    Trim would now allow preamps 1-24 to be sent to two different batches (sharing gains), each with their own trim.

    If not doing something like this I would say set the trims to 0db and use pre-amp gains.

    My 2 cents

    #31856
    Profile photo of smorgan223
    smorgan223
    Participant

    Allow me to offer a different perspective on this. You could set the gains for the pre-amps as hot as possible to keep the analog pre-amp warm so you are getting the most out of it. Then you would set the desk to use the trim in order to set your faders at unity gain. In the analog world, the gain and trim knobs are pretty much the same thing depending on the console you have, but digital has allowed the ability to run the pre-amps hot, and dial back with digital trim.

    Just a thought on the subject.

    Thanks,
    Scott Morgan

    #31863
    Profile photo of cctrieloff
    cctrieloff
    Participant

    Agree with the last post. A&H can be run hot which is one of the many reasons why I have bought so many A&H desks over the years. I would drive the pre-amp as hard as you can with the A&H analogue desks (great sound), and then trim it back if you want to.

    Mackie is cheap and cheerful – i.e. you just look at the pre-amp and it distorts and generally sounds terrible. Basically running first gain stage hot is the way to go, and is not something that Mackie can do.

    Carl.

    #31872
    Profile photo of BobWitte
    BobWitte
    Participant

    Many amateurs tend to run pre-amp gains too hot and under estimate the headroom they need for the energy of a live gig once the band gets rolling…. We consult at many churches and see way to many red lights during the “service” that may not have been seen in practice.

    With modern mixers and the low noise that quality systems have, make sure “hot” does not distort (mic pre-amp) or clip (digital) when the snare is slammed by the drummer or the vocalists “screams” or the bass player starts slapping the strings…..[:)]

    Bob

    #31877
    Profile photo of Ron
    Ron
    Participant

    Thanks to all who responded on this topic. I picked up some great insights from every response.

    I can definitely relate to how peak levels can increase between a sound check and the actual service. So I have found that leaving a little headroom is my best option to avoid the red peak lights from cropping up too often.

    Thanks again. This has been a very helpful thread.

    #31965
    Profile photo of KJREngineering
    KJREngineering
    Participant

    Here is an easy to use gain structure for most consoles digital or analog. Works best with a split mix for the monitors. Most of the touring guys I work with use a simple setup to ensure enough headroom for the pres and the channel strip as a whole, leaving room for EQ boost and dynamics make up gain. Start with the input trim fully attenuated, channel fader to unity, main fader to unity, then turn up the input gain until the desired SPL foer the source is reached. When you have a group of like instruments say drums do this one channel at a time setting each channels volume in the mix with the input gain, once done with the group, eq them all, set your dynamics and “re-mix” them with the input gains. This leaves all you channel faders at unity where they are the most responsive within the audio taper of the fader allowing you to mix using very small fader movements. This method also matches the output of the source to the system better allowing for less bleed and leaving the mic focused on it’s source instead of entire ensemble or band… Give it a try! In analog world this method will give you an excellent signal to noise ratio as an added benefit!

    BKool

    #31968
    Profile photo of Chris93
    Chris93
    Participant

    quote:


    Originally posted by KJREngineering

    This method also matches the output of the source to the system better allowing for less bleed and leaving the mic focused on it’s source instead of entire ensemble or band…


    Proper (input) gain structure matches the output of the source to the system, absolutely. [:)]

    The setting of the input gain has no effect on what the mic picks up, only how much that signal is amplified. An unplugged SM58 rolling around on the stage is “on” and is producing signal at it’s XLR connector (assuming there is sound present at the mic).

    Any isolation of sound sources happens because of microphone polar patterns (point it at what you want to hear, don’t point it at other stuff) and relative proximity (put it a lot closer to the source you want to hear than to other stuff).

    Both of these result in the intended source providing the majority contribution to movement of the mic diapragm, and happen well before any preamps. (I suppose frequency response plays a part too, a darker mic would pick up less overall hi-hat than a brighter mic).

    Try recalling scenes that turn down the preamp and turn up the channel fader the same amount.

    Chris

    #31973
    Profile photo of KJREngineering
    KJREngineering
    Participant

    Chris93, while I agree with the electrical engineering theory of what you posted. Try this experiment, take a mic in a fairly live room, open the gain all the way, record it, then halve the gain, record it, then halve it again, record it. You should find wide open you will hear the whole room, at each halving of gain your “world” will shrink making sources father away fainter less prominent in the recorded “mix” making the mic “sound” intimate and selective to the source to the source.

    To all running a pre-amp hot is wonderful if you are looking for a harmonically rich content, many pres can even be clipped slightly red lights and all and you will not hear the distortion, only a warming, this is very true when the slew rate of the pre exceeds the psycho-acoustics of the human ear and allows it to recover before your ear can detect the hard part of the clip. This was an 70/80’s trick to massive sounding rack/floor toms. I saw an interesting demo of this way back maybe 30 years ago when chipsets got faster and have used it to good advantage many times! That said harmonically rich is not always the proper mode for all music and instruments

    Digital clip is another matter, and really not to be induced, if you like your job at FOH…

    BKool

    #31979
    Profile photo of Chris93
    Chris93
    Participant

    quote:


    Originally posted by KJREngineering

    Digital clip is another matter, and really not to be induced, if you like your job at FOH…

    BKool


    And then you have the wonderful fun of preamp sharing when one engineer wants to clip and one doesn’t. [:D]

    I’ll try recording the open mic with different gain settings and see how it goes. I haven’t found it to make any difference to overall gain before feedback though, which seems like the same scenario.

    Chris

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