Trim

This topic contains 10 replies, has 7 voices, and was last updated by Profile photo of splatterelk splatterelk 10 months, 1 week ago.

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  • #107561
    Profile photo of MiG Eater
    MiG Eater
    Participant

    Hi all, could someone kindly explain what Trim does? I understand it’s a digital version of the Preamp but I don’t know why and when I need to use it. The manual doesn’t tell me much.

    Thanks!

    #107570
    Profile photo of KeithJ A&H
    KeithJ A&H
    Moderator

    @MiG Eater

    It’s not really digital version of the preamp even though both are gain stages at the beginning of the signal path.

    Preamp gain is a gain stage that is only positive/additive. In the SQ (and all of our digital mixers) the preamp gain setting is controlling a physical, analogue preamp which is connected to an XLR input.
    The preamp consists of preamp gain (0dB to 60dB) a 20dB pad (for hot signals) and 48V phantom power.
    This lives directly after the input socket and before the signal is converted to digital, so it’s worth noting that when using expanders, this preamp is in the expander and is controlled from the desk.
    Also note that even though the preamp can be controlled from a channel (in the processing screen) and settings can be stored in a channel library, because it’s a separate physical thing, it is not actually a part of the processing. For example, you can control a preamp that has not been patched to one of the 48 input processing channels by touching the socket number in the I/O screen.

    Trim on the other hand is a digital gain stage which does exist as part of the input channel processing.
    It allows you to increase or attenuate the input signal with a range from -24dB to +24dB.
    You can use it to adjust the signal on a particular input channel without altering the analogue preamp stage.
    This is useful whenever two things are using the signal from one socket and you only want to make a change on one particular channel:
    – FOH and Monitor digital splits
    – Double patching of a single source with separate processing
    – Recording/streaming post preamp or using tie lines (where you don’t want to make lots of gain changes in post)
    Trim is also used to adjust the level of any digital input signals i.e. those coming from another system, option card (Dante/Waves/MADI) or USB.

    Hope this helps!
    Keith.

    #107575
    Profile photo of MiG Eater
    MiG Eater
    Participant

    Thanks so much Keith, I really appreciate your time in explaining that! Legend.

    #107619
    Profile photo of WaihekeSoundie
    WaihekeSoundie
    Participant

    That was so helpful!
    Thank you

    #108991
    Profile photo of Bones
    Bones
    Participant

    Hi,

    Very clear explanation indeed, thanks.
    However, when recording a multitrack session through the USB-B to my DAW (ableton), the trim setting still affects my input gain in the DAW. I’ve set the global direct out source to post preamp.

    The issue i’m having is that my DAW adds an additional -18db headroom, compared to the SQ-6. By trimming, I would love to even out the gain difference between the SQ and my DAW. Is this possible?

    Thanks

    #108995
    Profile photo of KeithJ A&H
    KeithJ A&H
    Moderator

    @Bones

    It is slightly confusing, but the ‘post preamp’ option for input channel direct out does also include trim as you can see here – https://www.allen-heath.com/media/SQ_ReferenceGuide_V1_5_0.pdf#page=109&zoom=200,-147,39
    This makes more sense when considering the trim is the only way to adjust the level of a line or digital signal.
    The best way to record directly from the preamp without any processing, is using Tie Lines. These route signals directly from any input socket (analogue or digital) to any output socket (analogue or digital), so for recording, you could patch your local input sockets directly to USB output sockets. As in my previous post, the only things that will affect those signals are gain, pad and phantom power, being that these all ‘belong’ to the socket you’re patching from.

    The headroom is not added by the DAW, but due to the SQ sending the signal to USB directly from the core.
    The difference between the metering on the SQ and that in your DAW is explained, along with options for ‘trading in headroom’ if you need to, in this article – https://support.allen-heath.com/hc/en-gb/articles/4403616287889-General-Qu-SQ-Levels-and-Metering-in-Qu-and-SQ

    To answer your question more directly though (sorry!) –
    Yes, the trim will change the level going to the direct out and therefore to your DAW, but it will also adjust the level in the channel strip, which may not be ideal!
    Each input channel does have it’s own direct output level setting, which you can see and adjust by touching ‘Dir Out’ at the top of each input channel in the Routing screen.
    This can provide you with an extra 10dB of gain in exchange for 10dB of headroom.

    Hope this helps!
    Keith.

    #109008
    Profile photo of Hugh
    Hugh
    Participant

    Keith , this is extremely important info and advice for all of us that are deploying tie lines for recording. I use the SQ tie lines thru my waves card however I do not know if the tie line deployment direct from the analog circuit would also be available for redundant SQ-drive multi-tracking.
    From an operational point of view it becomes very important to establish a usable pre-amp db output level (the first step in basic gain staging) that avoids the spikes that can become problematic with some less than skilled performers. From what I have read in the recommended articles the SQ will deliver a reduced db level to prevent digital distortion in the SQ-drive protocol. Using the “Trim Knob” to increase the dbs is apparently not as safe as increasing the dbs in the DAW after capture. Given the large number of contemporary church services using SQ gear these days to distribute multiple sends for recording, broadcasting and streaming: practical advice along these lines will be very helpful.
    Hugh

    #109011
    Profile photo of KeithJ A&H
    KeithJ A&H
    Moderator

    @Hugh

    I can confirm that you can use Tie Lines to patch a single input source/socket to multiple output sources/sockets.
    Using what I know of your set up as an example, you could patch a PRIME input coming in on SLink input socket #1 to both a Waves card fitted in the I/O port and to USB for a backup recording to SQ-Drive or a computer/DAW via USB-B.
    You could go further still and tie line the same input socket (SLink#1) to a local analogue output socket if you so wish.

    Regarding the headroom, there is no reduction in level at any point. There is a maximum digital level internally in the SQ as well as in the DAW which is 0dBFS. This is when all bits of the sample are ‘1’ and no greater level can be represented. This 0dBFS level is 18dB above the 0dB marking on the SQ meters, so it is just a difference in measurement rather than an actual difference in the signal.

    In terms of practical advice, it really does depend on the situation, but in most where you are recording, it is possible to increase the level in post production without any issue, so we’d recommend keeping the headroom. You can boost the signal after the fact, but it’s far more difficult (often impossible) to remove digital distortion.
    Where it may be essential to increase digital output level in the moment is with things like streaming or broadcast, where there isn’t a post production stage!

    Cheers,
    Keith.

    #109038
    Profile photo of Hugh
    Hugh
    Participant

    Keith,
    Thank you for the clarification however at this point a source with an extraordinary large dynamic range is my primary concern. One of the referenced articles covered the detrimental possibilities of too little gain and we all are aware of clipping concerns when gain is to high. These issues are never a problem with session ready talent however given the problems some nervous novice performers exhibit, clarification pursuant to a best method of maintaining a useable gain signal in these situations would be helpful in deploying tie lines.
    Hugh

    #113781
    Profile photo of Phil
    Phil
    Participant

    Keith
    Can trim help?
    SQ5 = FOH
    AB168 = stage box
    I’m having difficulties in one of my venues with stage volume/noise…it’s much to loud (oddly enough the band doesn’t cooperate much). When I increase the pre-amp gain I also increase the stage volume/noise through the mic and therefore the PA (I know gating will help, but I’m looking for alternatives as well). Increasing the vocal pre-amp for each of the 3 mics on stage adds into the overall volume of the band through the PA. If I push it – I get into feedback problems. I’m wondering if ‘trim’ may help?
    I use Mix sends 1-6 for stage monitors; 7-8 are the PA
    Using a simple vocal mic (SM58) – Will increasing the trim on any input channel increase the volume in the monitor selected? or the PA? or both? or none?….or should I forget about trying to use trim as a solution? My goal is to push more volume of the vocals out the PA ONLY – without disturbing the mic/monitor set up/balance on stage.
    Phil

    #114735
    Profile photo of splatterelk
    splatterelk
    Participant

    Thank you for the clarification, but my primary concern at this time is a source with an extraordinarily large dynamic range. One of the cited articles discussed the negative effects of insufficient gain, and we are all familiar with the slicing issues associated with excessive gain. With session-ready talent, these issues are never a concern; however, given the issues exhibited by some nervous novice performers, it would be useful to have clarification on the best way to maintain a usable gain signal in these situations when deploying tie lines. gorilla tag

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